Brad, you electrical wizards have my complete respect. I have always been a car/metal fab guy for my recreational hobbies and have even done ground-up's on rust buckets with little drama. But as soon as I have to get behind a dash and sort out a wiring/electrical problem, I am all but lost. After a few decades I have resigned myself to the fact that it's never gonna sink in. I can't imagine dealing with an intermittent issue in something this small/delicate. I'd be crazy 10 min. in.
I've had similar occurrences recently, and in each case it was due to faulty coupling caps, which allow DC to pass to the next tube's grid and alter its bias. If you're monitoring the tube's plate current, it seems to "run away", until you either pull the plug or eventually smoke the tube. I believe the overheating cap(s) you commented on were coupling caps.
Always better to be certain your theory of the faulty part is correct. Replacement of parts you think are faulty leads to your customer paying for unnecessary work in addition to paying for what needs to be done, plus your reputation isn't enhanced by this approach.
PCB are crap. Yes there were good amps with PCB Early Ampeg, but Fender never made a PCB for its HotRod amps that last with daily performance with a gigging musician, maybe 5 years
I spent the last 10 years as a residential Maintenance Supervisor but I've always played guitar as well. I know that troubleshooting is 70% of a job typically. It's always a great joy watching your SPF's and repair videos. I've spent my entire life hanging around with folks like you, even though I'll be 30 this month. You are extremely relevant, and your content is ALWAYS highly anticipated in my life. Thank you for everything Brad, much love from Oregon brother!😎🤘
I would also test it in its cabinet. Your are letting a lot of heat out of the top of the chassis. plus the vibrations from being played from the speaker. Inconvenient i know but you need to test as it would be used,
Design failure 101. How to make a tube amp nightmare - have the tubes upside down; heat rises and slowly cooks your amp while you play. Fender, Gibson, etc. Learned this lesson the hard way.
I've been playing lead since 1963 and have owned dozens of amplifiers, some extremely nice ones. The two worst were a Mesa Nomad 40 that ATE EL84 tubes and had waaaaay too many switches and knobs, and more recently a Mesa 50 Caliber+ EL84 version which was unrepairable. Its problem was red plating that no local tech could solve. NEVER AGAIN.
Years ago I had a Mesa Boogie rectoverb combo that kept blowing power tubes, then had channel switching problems. I was the second owner, with no schematics and lack of resolve for fucking with the amp. There’s no accounting for how it was maintained before I owned it. I called Mesa and they told me to pull the chassis and tubes and send it to them for repair. They only asked that I pay for tubes and shipping. I got it back with all newer version boards installed. How nice is that! I finally sold it a few years back, and it was still an absolute fucking tank! The guy I sold it to still plays the living hell out of it.😆
I’ve been a technician for the phone company for 18 yrs and I can really appreciate this video. Trying to find intermittent trouble is every techs FAVORITE NIGHTMARE!😁.
@@DavidMFChapman I have a Mesa 50cal+ I basically got for nothing because the dude said he took it to a tech like 3 times in about a year and it just kept failing, so at that point it's like buddy obviously felt the amp was just a burden lol, but Im hoping i can come across a tech who can fix it! Or just change things out and hope it works lol, but I don't want to fall in the same cycle of spending money and have it keep systematically fail! The thing that's wierdest about it all is the guy won't tell me who the tech was but he can't tell me what the problems were so I don't know where to start. So either he's lying about even taking it to a tech, or he's telling the truth but it doesn't give me a very good place of where to start.
@@ETILHK54 unfortunately it's not always that simple. some components can measure fine with a tiny wee multimeter, and fail in smoke when you apply power to them (tantalum caps to the face). When they get warm, things move too. Poor solder joints, crusty sockets, ceramic caps, resistors.. all can measure great and be the cause of your problem, besides not all components can be measured precisely in circuit.
Before me there was a pile of amp chassis that were not worth repair or parts issues at the time several feet tall and as wide as the room. Hundreds of them. My job was strip them of useable parts. It looked like a lifetime job. The smell was also unforgettable. So as you struggle today remember many before you have had problems with repair and cost Many amps in that time were simply thrown in garbage after being stripped. Mostly cheaper brands whose name is all but lost in memories. Thanks for the hanging in there on this one. It's how one learns good job !
My Mesa Boogie 50 cal Plus has been a bad bad dog to fix, I paid $475 for the amp used on Ebay and i have already sunk $875 into repairs and it still doesn't work right . The issues a) the sound cuts out and sounded harsh harsh harsh and of course this was intermittently b) when i turn the amp on all you hear is loud static and crackling noise c) when i use the foot switch to go between the clean and dirty channel there is a huge huge spike in volume, the volume spike could knock a freight train of the tracks, i swear. THE FIRST REPAIR GUY replaced many of the smaller tubes, not the power tubes, repaired many cold solder cracks, and some general cleaning of electronic parts inside, cost $275. THE SECOND GUY replaced all the capacitors and replaced the two power tubes with 2 used Groove Tubes, that's right this guy replaced old tubes with used tubes that he said could not guarantee how long they would last. for his work he charged me $600 . Between the two guys it cost me total of $875 and the amp is still not working right. I made a couple phone calls to Mesa Boogie, THEY COULDN'T HAVE BEEN NICER , REALLY TOOK THE TIME TO TRY AND HELP ME OVER THE PHONE, BUT IN THE END AMP STILL NOT WORKING CORRECTLY. I can't even sell it if i wanted to the way it crackles and hisses . Anyway, I don't know what to do with it other than taking the Chassis out and sending to Boogie , but that will be expensive, i like the amp but damn there comes a time to walk away .maybe i will put it on the front lawn with a " FREE " sign on it.
completely build the bias supply and circuit off that main board. when troubleshooting , use two meters to monitor the bias on both sides at the same time. Its a very bad idea to have +400 or more volts very close to a negative voltage on a PC board. Marshalls were plagued with this problem and the fix was to drill out the board from around the bias pin and run flying leads to it. I have seen that cracked board scenario as well quite a lot. Using cheap PCB material with thin copper cladding is a bad idea but bean counters love it. Also that "bubbling" you say you saw is often solder flowed under the mask. not usually air gaps. WHat i often do is scrape off the mask from a board and lay down a bare copper wire over the trace and solder it along the trace to 1, ensure its continuity and 2, beef up its current carrying ability. This would work well on that output tube board and save all the drilling but i would have still isolated teh bias pin and put that circuit on a daughter board or flying leads....my 2¢
Barry Beadman Yes! I have done that at times when a board more or less ‘must’ be kept... It is appalling how shitty some boards are laid out without regard to high voltage spacing, and current capacity of the trace foil. Too many idiots doing the work.
I know many have commented on your drilling and your drill. I have a riveted-in, broken socket to replace, on my bench. So, I'll be doing some minor drilling on a fully loaded wired chassis. My tip is--and I've never used a "step" drill bit (so, this may not be as effective for that)--always use a drop or two of oil when drilling metal. Put it on the bit or the piece. You can actually use Vaseline--I kid you not--it will make the job smoother, the flakes will be more like metal ribbons, the hole will have less burrs and it will make your drill bit last longer. I never drill metal without lubrication. I keep a small lever-pump style dispenser, filled with Marvel Mystery Oil, in the shop for small lubrication tasks like drilling, etc. But the Vaseline trick works when you don't want liquid running into other parts, or you're drilling overhead, or outside on a ladder. It melts and lubricates and makes the drill job much cleaner and smoother. As for the amp, some players tilt their amps and that could cause areas to heat up that normally wouldn't when you have it horizontal on the bench.That amp, when tilted would cause heat to flow to the big board? So, you might try running it tilted, for an hour or two--or ask the player how they configure the rig. Do they stack shit on top? etc.
Better you than me. I stopped servicing Mesa Boogies a couple years ago. They just eat up time. Got tired of feeling lucky to break even on them. Over complicated designs stuffed into tight spaces. Stacked pcbs. More FETs than you can shake a stick at. Excessive heat build-up. I feel bad for you man. For me, this just reinforces my decision to shun Mesa Boogies from my bench. Thanks Brad
Hi Brad, I just thought that I'd comment on Mesa amps that I have owned and a DC3 Mesa that a friend of mine owns. I have owned a Mesa Tremoverb amp since 1995. Bought new here in Canada. Cost me a king's ransome to buy here. I have had nothing but trouble with this amp since the day I bought it. Just recently sent it all the back to California for repair. The trouble with Mesa amps, is when something does go south mate, you're pretty much screwed trying to find someone to repair it. PC boards are nothing but trouble in that respect. I currently own two Ceriatone amps and they are both point to point wired. Makes repairs relatively easy. Never had any problem with Nike's amps from Ceriatone. My Tremoverb is back from Petaluma and it does work now, but the noise floor is horrible. It has Voodoo amp mods from Voodoo amps. The amp doesn't sound bad, but the noise floor is pretty bad. I still think that this amp should be a boat anchor. I would never buy another Boogie. Too fizzy sounding in the red channel stock, like a can of bees. The amp is also way too brassy and compressed sounding. I also have a Mesa Revolver Leslie speaker that seems to be going south. A Canadian actually invented this Leslie. It's great when working well. Their amp cabs are very well built. The seems like It's very well built, but the sound is not something that I personally like. I also think that dealing with Rich at Mesa sucks. You would think that they would have tried to do something about the noise floor problem. Do you know Brad, whether or not you can use GZ34 rectifier valves in a Mesa Tremoverb amp? My friend also has a Mesa DC3 with nothing but problems.The board that those valves were mounted on are terrible. Fender builds the same shite.Take care , love your videos Thanks from Michael Newell from Niagara Falls, Ontario, Canada
I think you were definitely on track regarding that cap that was getting warm on it's own. That should never happen, and since one end was to a high positive voltage, leakage there would take out that portion of the negative bias. I think you got it dude! Thumbs up!
Brad, man, thank you for doing these videos. No shit, watching your process has helped me be a better paramedic. I even used parts from a couple of your videos to teach my medic students. Watching you trouble shoot and rule things out is essentially the same kind of differential diagnosis process we use. You and the old NPR program Car Talk are perfect examples of how to diagnose through elimination. You’re saving lives, brother!!
Hey Matthew...I certainly hope you don't use complete process of elimination with your job...and the idea of you with a solder sucker in your hand has to terrify your patients. :-) BTW.. I been working on electronics , for like 50 years now and I really can't see you doing anything else to check for loss of bias. Just the one, as someone previously said. A heat gun, put it back in the cabinet or case and move it around like the owner would do with gigs. You did a great job changing out that funky tube board with hard wiring. Definitely a weak point in the design. Those tubes get pretty hot for a normal guitar amp's baseup placement. Crack in the board wold be a real PITA. Reminds me of a few SVT's I've worked on. Everything has to come out , and I mean everything to change the cave type jacks. Inputs and outputs cheap plastic sealed jacks CRAP! in such an expensive amp. no!................arg! Of course Ampeg isn't owned by the original company anymore. And as you said about mesa boogie Customer service is super over there.
Man, I was going to dump my old Dean Markley CD 120. I am 3 inches shorter just from carrying the monster around. But after opening it up to compare build with your videos of the Mesa's, I have apologized profusely, say nice things to it constantly and occasionally smoke a bowl with it. We're friends again.
I won't touch 'em any more. Life is too short to be unhappy. The last one that showed up had switching problems. I counted 33 knobs and seventeen relays and only G-d knows how many FETs that represent potential failure points not to mention the three rectifier tubes and what-six or eight power tubes?. Away it went to Petaluma with my blessings.
I spent months trying to get the hum out of a simul 290 power amp. I spoke to Mesa and their response was "it's supposed to do that". When you switch the modern function on it would hum, it adds a cap into a feedback loop and acts as an oscillator. That's just one example, I have numerous Mesa repair nightmares. It doesn't help the schematics are inaccurate. Just look at the layout of the PCB it's a mess. Looks like they threw components at the board and where they landed that's where they etched traces.
The legend that is Walter Trout had one of these start misbehaving during his Glasgow gig just last week. He most definately was "not" a happy camper. LOL
Yeah, Mesas are bad, but look at the inside of say a '74 Ampeg VT-40...I had no idea how they put that together, let alone how to get it apart....THAT was a pink nightmare
I bought one of the first Mark 1 amps from Prune Music in Mill Valley in about 1976. Biggest headache ever produced by mankind. Sal, at Prune, had to service it several times until I gave up and sold it. And that amp was way more simple than this thing.
I'd suggest 2 things. One, get a drill press. Two, don't drill metal shavings all over your ELECTRONICS work bench. I enjoy your repair videos and have been watching them for a couple of years. Your SPF and rant videos, not so much. Hope the repairs work this time.
From a safety standpoint, the drill press provides much better control, avoiding the handle windup on the hand drill. Also, with a drill press it is much easier to control the depth step that you want to reach. I've drilled a lot of holes in a lot of chassis and wouldn't do it without the drill press.
I have had 2 mesas. Both had issues that were very difficult to find. On a 50 watt Son of Boogie, it would intermittently cut out while playing but when the chassis was on the bench, it worked perfectly. I found a resistor covered in a glob that I used a dental pick and found it wasn't soldered in. After that, the amp worked. The second amp, I sent back to mesa and they had for several weeks and sent back. Same issue, and an unsoldered resistor.
Intermittent problems are a pain in the butt! I can remember doing service work and driving 2 hours to a job, to find the equipment was working fine. Drove back to the shop to be told it failed again! This was before cell phones. Then took another 2 hour drive...insanity!😵
@@InTheSh8 ya, after messing with all the adjustments...was a commercial gas fryer that was sold before all the bugs were worked out of it! Factories did it all the time!☺
Vibrations, all my combo amps seem to develop issues from constantly being in a vibrating box with a loud speaker. My guess would be something to do with that if you haven’t already got it fixed. Also I’d check it with the thermal imager again and see if the new caps are running cooler or not. Enjoy seeing videos like this. I don’t really repair amps but I have an interest in it and have done some electronic repairs on other things in the past. I like that you let people see how challenging things like this can be to find and repair. Intermittent problems on anything are a real pain to deal with.
Hey Brad, big fan of the channel but never comment. I also tech, repair and own a handful of vintage tube amps. I have seen this same scenario before in my early 70's Ampeg V4B. If the problem was in the bias power supply it would show up across all four tubes but since it is isolated to just one pair you know that it has to be somewhere just in that half. The coupling caps that feed the signal from each half of the phase inverter to each pair of output tubes have to block the DC 200V+ plate voltage from the inverter to keep it off the bias/signal feed. When those caps start to get leaky they will let some of that plate voltage thru and the bias will drift because of it. The thermal image shows those caps were working harder than usual too indicating that they are towards the end of their life. Cant blame ya for rebuilding all the other components however, its good insurance. The last thing you want is any amp coming back, especially for a 3rd time. But I am willing to bet that the root of this issue was due to one of those coupling caps failing. Always enjoy your videos!
You could try heat gun (or hairdryer) and freeze spray routine to try an force a failure. Got to be careful with the heat obviously. Generally a technique that would be more useful for design debug as you can afford to kill a unit.
Brad: a helpful thing I found for step bits is backing them with a bit of wood. It slows them down and keeps them from binding in the sheet metal (caused by them trying to take too much at once). Gets a bit hot after a while though, so care is recommended. EDIT: Looking at the schematic, the resistance from the grid of the tube to ground exceeds the maximum rating of the EL84 (300k). This makes it possible with some tubes for grid-leak biasing to take place. I don't know if that is what was happening here, but it is important to note this spec when designing amplifiers.
I hate working on MESA stuff almost as much as I hate working on Marshall TSL and DSL amps. Intermittent problems take a lot of time and are a dead loss for the tech. Customers blame the tech for not getting it done in one visit when they should be blaming the amp company for designing unserviceable equipment. I keep sweet grass and holy water on hand for intermittent stuff because sometimes it's as though you're battling a demon.
As a tech, a necessary skill is explaining to the customer that the repair process is just that.... A process. Sometimes you have no choice but to do process of elimination. Explain that to a customer in advance and you make everyone's life easier.
I've been in Music and Music Electronics for over 50 years and have been an authorized Mesa Repair center for over a decade. I have great love and respect for Mesa but I sincerely think they need to up their respect for what their demographic is even if it means hitting a higher price point. Mesa's reputation was built on ultra high quality in performance, reliability as well as beauty and primarily targeting professional and semi professional users. Frankly IMHO mesa should never release an amp that has tube sockets attached directly and only to a PC board. They should be above that if they want to maintain the great reputation they grew on. Either that or specify what models are built down to a price point for hobbyists and casual users. Intermittent issues are the worst and they most often happen with mass production design like PC boards which are also the most difficult to diagnose and repair. That's not a huge problem at preamp levels but it is inexcusable in the power section of a supposedly road-worthy amplifier. It is possible to quibble over minor points of how you approached this repair but the bottom line is it began with stupid design. There is a reason that there are still original Tweed Fenders on the road after 60+ years. They are simple, rugged, rarely breakdown and are easy and cheap to fix when and if they do. That's just hard to sell on the showroom floor. That takes years to build as a reputation of accomplished fact that translates into a reasonable expectation, but it can be lost in a very short time. Mesa should remember how Vox fell from "Mt. Olympus" and took decades to recover.
@@jixxxxer17 It isn't hard to find out. If the Bullet Point List doesn't show it, but you can see internal photos or the actual amp, it' s immediately visible on the chassis. If all else fails call Mesa! They are really nice people and quite willing to help out. Randall obviously runs a very inspiring workplace because many key employees have been there for decades... some pretty much since it started.
@@enorbet2 Scottie @ Mad Creations is the guy who worked on it he took photos of the inside of the amp including sockets I ll see if I can tell anything from those pix, thanks again for helping. Peace
@@jixxxxer17 NP. To be clear if the tubes go through a hole in the chassis they are PCB mounted. Sockets mounted directly on the metal chassis are easily visible and will have mounting bolts. No mounting bolts are usually visible on the chassis near the tubes with PCB mounts with the very rare exception of a few that mount a tube retainer device on the chassis but Mesa doesn't do that AFAIK.
Great to see your expertise again on amp service! Not that I don't like your other videos, they are great to! Mesa should go back, at least once, and rebuild a Princeton amp chassis with a Twin-Reverb circuit or Super-Reverb circuit and put a 12 inch 100 watt speaker in the cabinet like he did for Jerry Garcia! That was his finest hour! Love ya Brad! Thanxz
hey. if i understand this right you have your bench in the basement. why not to put some noise isolation and just play a looper pedal into an amp and then probably come and check it from time to time to see if it fails?
I had the issue of red plating on my DC-3 not long after I bought it in the late 80's and spoke to Mesa Support and they told me the clip retainers sometimes short the contacts, I removed them and never had that problem again. Not sure that was the issue here but wanted to share my experience.
Maybe the primary side of the output tranny is shorting on one side (the side that's red plating). The lower inductance would draw more current. Once the copper wire in the tranny heats up it'll expand and lock in the short until you turn-off the amp which colls/shrinks the copper. I would image playing live where the wire in the tranny could vibrate would create a scenario where the short is more likely. Could gingerly use a hair dryer to warm-up the tranny to try to engage the short.......also artifically introduce some vibration to the tranny.
Mesa does not usually do simple :-) Luckily their gear and their support is usually very solid. That amp has likely been working well since the early 90s - so what - 25 years old?You can expect problems in a 25 year old amp. I do enjoy working on the simpler vintage gear more, so I understand where you are coming from.
Keep everything as simple as practical, for sure. For an amp, all I need on it is a volume knob. I control everything through my pedal board, anyway. My pedal board consists of a modeler with wah pedal, and a surge protector power bar for my amps and whatever else I'm using. I take the extra time to tweak my presets so the amp only has to be loud and clear. More shit means more shit can go wrong. I play my own music, anyway, so I can sound any damn way I please!
I' myself Have been working on electronics , for like 50 years now and I really can't see you doing anything else to check for loss of bias. Just the one, as someone previously said. A heat gun, maybe and you should put it back in the cabinet or case and move it around like the owner would do with gigs. You did a great job changing out that funky tube board with hard wiring. Definitely a weak point in the design. Those tubes get pretty hot for a normal guitar amp's baseup placement. Crack in the board wold be a real PITA. Reminds me of a few SVT's I've worked on. Everything has to come out , and I mean everything to change the cave type jacks. Inputs and outputs cheap plastic sealed jacks CRAP! in such an expensive amp. no!................arg! Of course Ampeg isn't owned by the original company anymore. And as you said about mesa boogie Customer service is super over there. BTW I'm from Philly and it really cracked me up to hear your impression of Fran! Hahaha Hi I'm Fran Just putting together another Mars probe here in the lab with spare parts Hey everyone SEND ME MONEY...Please for my experiments! Which everyone does because we love Fran here. Now you need to get your impression of Benny Cintiolli down and you'll have Philly covered. His favorite line in an Italian accent is : You Don Wanna a Mahhshell You Wanna a Hampeg! :-)
Thanks for posting this very detailed and informative vid. Although I don't forsee any occasion arising where I'd be doing this kind of repair, I do LOTS of home repairs that are less technical and I am always interested in seeing how repairs that are beyond my abilities are done. No matter how hi-tech a repair is, re-sizing already existing hole by drilling to accomodate replacement parts is a common enough situation I encounter, especially when buying things that come in "kit" form requiring a lot of assembly. Also, I electroplated PC boards for two different companies during my employment years and I found theblow-ups and explanations of the component paths and points very interesting. 👍
yea, guys where I worked laughed when I bought a FLIR a while back, but that thing has saved me so much time, in tube amps, and especially big solid state monsters... and every day someone would borrow it! lol
Intermittent issues are the worst. In this situation you can try using a hair dryer (carefully) on the part of the board that you think might be failing when it gets hot. Then use freeze spray (which is more local) on each component to see if it recoveres.
Sort of piggy-backing on earlier comments. I used to work at NASA, although not an engineer. Our standard was to test it as you would fly it. Whenever we decided to save a little money and just test at the sub-assembly level but not test at the system level, in a real environment, we were nervous as heck. I can point to several examples where unexpected stuff happened after launch and we did not have the data to understand why. You may want to lock the reassembled amp in a room someplace and run some programmed music through it for 24 hours. After having some bad experiences, I would do this with any new stuff I would buy that was manufactured in China or made by Peavey. Lord, just the nasty smell from cheap paint, glue and particle board solvents being boiled off was amazing!
Thanks Brad! Nice job! I have never worked on one of those amps before but I would go ahead and replace the diodes just to be on the safe side. Also, I would flip the amp around 180 and recheck my solder connections. A couple of times a solder joint that I made looked good in front of me but when I looked at it from a different angle it wasn't so good.
Intermittent problems are the worst. You followed your gut feeling on this and if you ran it hard on the bench,,, nothing more you can do Brad until the meanie raises it's ugly little head again. I think you nailed it this time.
Something i ran into a lot. Watch out for plate resistors (100k,220k) on 12AX7’s opening up under heat. They look fine, but under heat they open up. Some off them generate a crack that you just cant see. This happened a lot on Peavey circuit board tube amps as well as several boogies. I don’t think its the problem here, but its something that happens! A lot. Unless its a cracked or broken trace? I think you got it. You obviously didn’t need to build out the output board, but i agree it’s better off. I love boogie tone, but they suck to service.
Installing discrete components in the power stage is going to greatly extend the life of the amp, that board was going to shit the bed sooner not later. You've been very thorough, unless it's a cracked trace that only pops up when it gets hot, I can't see what it would be.
I have a Mesa Nomad 100. I have been having an issue with feedback at random times on ch. 3. I noticed even when I turn the volume knob off it still has feedback unless I switch to ch. 1 Clean. After my gig, I changed out V3 & V4 to see if it was a microphonic issue. Then, I discovered that 2 of my 6L6 tubes guide pins broke. I replaced those, then suddenly the clean channel stopped working? V1 was difficult to get to and the tube was not going in the socket like the other sockets. The feedback situation is weird, because I use a noise gate at the input and at the fx loop. I removed all the gates, switched out V1 numerous times. Got the clean channel back briefly. I got my amp used almost a year and a half ago. I had to replace V1 about 3 months in to owning it. I only run it 50 watts. This amp seemed to be barely used when I got it. I do not like the reverb that is built in. I have been thinking of removing it. I was wondering if it could be used like another fx loop. For example sending another EQ to any combination of the channels. Also, there is another piece of wood behind the baffle. I am wondering if it is possible to remove it to improve access to the preamp tubes. I don't like having to flip the amp upside down to access the tubes. The reverb tank removed may improve access. I could put a panel over the reverb tanks cavity. I think that all is wrong is the V1 socket. Maybe a new set of preamp tubes. Will removing the reverb tank effect the amp?
Good God! I hate working on Mesa. I had a Studio 22 on my bench 3 times. The circuit board was charred from heat and randomly creating carbon paths. I love my Mesa D800 bass head but would never own their earlier tube gear!
I've owned a '92 Studio .22+ since March; had it out on a handful of gigs & a bunch of rehearsals/recording sessions since early June. Zero problems. Maybe I'm lucky? I know heat is a serious issue with these Studio/Caliber amps, so I always give the amp plenty of breathing room and turn it *completely off* if I'm taking a break longer than 5 min. I suspect that folks leave these little Boogies sitting 'on' for long stretches, pressed flush against the wall, or what-have-you....leading to frying/glitching circuit boards.
The kings of charred pcbs are the Fender Hot Rod style amps, Blues Jr and the like. Bias is always set ridiculously high, tubes upside down and a PCB are a recipe for disaster.
JazzzRockFusion-your Studio 22 that you got in March probably has already been serviced. I have one that was built in 1986 and I did a whole cap job myself and also found a couple resistors that were so burnt out that they were cracked in half! Brad’s videos saved me a ton of money because the local Mesa dealer wanted $200 to fix it, and I spent a grand total of $40 to do it myself! Since then, I took it to one gig and a few jam nights and she stands up well to all my friend’s hi dollar new-fangled equipment!
@@dankress8228 $200 to repair the amp is a song. Great that you knew how to fix it but if you ran that shop would you feel comfortable charging a customer $40 for your work?
photopicker The local Mesa dealer first wanted $80 just for me to walk in the door with that amp! Still gotta say I’m way ahead since the new Mesa Fillmore series that I like costs $1600. Even if I did end up paying them to do the job I’d still be ahead.
Sometimes a tube can suffer from something called Ion-Migration between two pins if the voltage-difference is high enough, basically the Ion-Migration between two pins causes the glass, that's used to create the envelope, to become slightly conductive, and if it happens between a pin connected to the grid and say a pin connected to a cathode, that can cause the bias to go into runaway, resulting in the tube red-plating, I remember reading about this in an article in one of my Silicon Chip magazines (it's a DIY electronics magazine we get over here in Australia), the guy who wrote the article was doing some servicing work on a vintage tube radio, and couldn't work out why a tube was red-plating, eventually he discovered that the tube had been suffering from Ion-Migration that had developed between two pins, but I think that the most likely cause of the red-plating in the Mesa Boogie was one of those .047uF coupling caps on the grids of those power tubes, my guess is that maybe one or both of them were going intermittently leaky, the leakage is probably what's causing them to get hotter than normal.
14:15 The Seymour Duncan Convertible is actually easier to deal with - all the controls have little pins that the wires can disconnect from. I sure wouldn't want to have to pull that main PCB out of that Boogie... big P.I.T.A.
the 47nF coupling cap from the phase inverter shown on your thermal imager must have been leaky transferring the plate B+ to the negative bias circuit in effect reducing the negative bias allowing one pair of EL84s to red plate. The reason it only happened on one side of the output tubes is you have the isolation from the bias voltage divider and grid blocking resistors in my opinion
What did the bias supply caps look like in the thermal camera after replacement? Were they still getting as hot as they were prior to replacement? How about tube temperatures? Did they even out after setting bias and replacement of bias supply components? Or are they still uneven? I think these characteristics could be telling as to whether the amplifier is "cured" or simply seems ok and is just a ticking time bomb.
To induce a thermal expansion trace fault I might even throw a heat gun at the top of the the board, on low and at a safe distance. On the bench no heat will accumulate in the chassis as it would mounted to the cabinet. Alternately, you could lay a board on top of the open chassis as you let the amp 'cook' for a couple of hours.
the problem is quality guitar amps and electronics for that matter started on a downhill path to crappiness in the 70s prob more like the late 60s even.thats why people love old gear, they can get something refurbed and it will last another 50,60,70 years. plus the circuits are unecessarily complicated. i have a early 80s carvin x-100b at my house which i got working but only the lead drive channel when ever i try to switch to rhythm channel the leds change but the sound drops out.when i put it in lead drive the rhythm channel led gets super dim. looking at the schematic made my head spin being that i like simple basic old style design. there are no more nor no less components than needed usually. the carvin has a handful of transistors and another handful of ic mostly op amps but i am just lost with all the bells and whistles. give me pure raw tone and i am a happy guy. plus the more complicated the circuit the less i can hear the true tone of my guitar.
I believe I mentioned something on replacing/repairing that board on the first video lol. Just from past experience I can tell that board has been severely overheated and mounting the tube sockets to the chassis. We did the samething with my Carvin X50B after it caught fire because of that same crappy design of tube sockets on a pc board. It's such a terrible design on a good amp.
It may not just be heat, but the actual vibrations from the speaker that is causing a cracked component or connection to develop an intermittent fault. What did your little component tester say about the condition of those hot running capacitors?
You must have missed the part where he vacuumed up all the shavings. I've seen hundreds of Brads video's on various repairs and he is anything but lazy. I'll check out you're video's on this subject for a cross reference,,,,,,oh wait!
Umm.. but he Still didn't deburr the holes, which is important. It doesn't take long to grab a file and knock those off, ya know. Laziness, indeed ..and if you need a video to show how to do that, then you don't need to be working on amps in the first place! Lol. I even would've went a step further, and covered up the bare metal on the freshly drilled holes with a little bit of paint, because a steel chassis w/ bare metal is going to eventually rust. That's common sense to most, but what do I know... ¯\_(ツ)_/¯
@@R3TR0R4V3 Just because he didn't show it doesn't mean he didn't do it. Looking at the video again i do not see any burrs or anything of concern that would hinder the function of a socket that is riveted to a chassis. I didn't see any rust in there needing to be painted, i'm sure the owner was more worried about the red plating and if the customer is happy with the end result than that is what matters,,after all he or she is the one paying for the repairs and bench time.
Hi Guitologist. You should definately change the 470R screen resistors if they are located on the board ..if you haven´t done that so far by rewiring the Output Stage.... they ARE prone to fail after all our experience and should be changed. Have you checked the tubes first?(at least against each other in failing stage) Cut out the Electrolytic in the Bias circuit… you don´t want the amp to come in again won´t you :- ) Good luck!
I think fixing amps that do this kind of thing are fun to try to fix at first, but there's a point when where you get passed it, you immediately want to trow it in the garbage!
Those large step bits and steel chassis (i.e. Hammond amps) doable but not easy. I’m afraid my cheap but very handy drill/driver is gonna start smoking every time I use the big step bit. Still going strong tho!
