First an Uncle.Doug video,, now a XrayTonyB video! WOOT! To square it off, all I'd need is a JohnAudioTech vid and a Mr. Carlson vid. Thanks for sharing with us. Your style is such a refreshing relaxed "walk" through the thought processes behind bringing your projects back to life and more up to snuff. And please, your job helps save/diagnose/extend lives. I'd rather you wear those "angel wings" before worrying about the rest of us. Whenever you get to it is fine by me.
Ps, there's many more, like D-Lab, 12voltvids, Greggs Vintage workshop, shango066, learnelectronics, Blueglow, the audiophool, and.a bunch of other less prolific creators. I even go back and revisit some of those who are no longer with us like Steel Wheels Down and River Huntington, a couple of nice fellows lost to the big C. You never know who you touch in your life. I just thought you might like to know "you're doing good." Thanks again.
Hey, check out Usagi Electric, CuriousMarc, Glasslinger and Tony Albus if you don't know them. I'll be going that direction too, I'm greatly inspired by MCL :)
I just picked up a 240 that I’m excited to restore! The relay is VERY loud on startup, so the power supply is going to be the first thing I attack. Thanks so much for all your videos! It’s a college class every time
Best part of Tony's videos is he patiently explains the concept of the circuit, emphasises on basics and tries to explain the problems and solutions he has devised. Tech's usually don't share the technicalities and their process to troubleshoot. Sharing the knowledge is the biggest contribution to the community.
Tony is creating the greatest adventure story ever repair g and instructing all the viewers! So much learned, it's incredibly unselfish to spread this information to rarer eyes and ears! Brilliant!
I always impressed with your knowledge coupled with great test equipment, I bet the training you give your crew is better then any electronics school, To bad you cant take us to work.
Yep, a first gen version of a 250, in this version the MR752 bridge diodes are on the back relay board, they would overheat to the point that the diode pills would fall off the leads, in the later version they were relocated to the top of the big filter caps with some extra copper to keep them cool. Thad later version had machined pins to connect the E B pins and the wired sockets were removed. I worked in engineering at Marantz and the story was the engineer that did the original 250 would use resistor substitution boxes to get values right! He as gone by the time I got there.
Many years ago, I was going to buy a 250M at a local stereo store and the sales person was demoing it to me hook up to a SoundTech distortion analyzer. It was good until he set the frequency to about 20k at full volume and the magic smoke came out of it. He talked me into getting the next model up which was the 510 (no M) for $100.00 more money. I am glad that I went that route. It is very interesting that you are featuring one of them on your bench. I can't wait to see part 2.
Hi Tony, another great video! I noticed in the opening, behind you sat what appears to be a Tektronix 576 or maybe a 577 curve tracer. I know not many folks would probably have access to an expensive piece like that, but it would be interesting to show what that bad germanium diode looks like on the curve tracer compared to a new one. Can't wait for part 2!
Thoroughly enjoyed this troubleshooting video Tony. It is hard to fathom some person gave the approval to go into production on this design; train wreck waiting to happen at the first party where the owner really pushed this amp. Really looking forward to the next videos on this unit; thanks for your time!
What a tricky repair. I imagine that we can scratch our heads without old analog multimeter. This is a good example of why we need to keep our old test equipment up and running!😉. Awaiting part 2….
I frequently use an old Triplett analog meter at work (audio repair shop). Excellent for quick in-circuit tests of diodes and transistors, and capacitor charging/discharging, without the jumping around of a digital display.
I always enjoy your videos. I work on vintage audio gear myself. Started working on that sort of gear in the late 70's, when much of it was new and under warranty. If for some reason I needed someone else to work on my gear, you would be one of the few people I feel I would trust to do it.
Wow..this was great detailed diagnosis and troubleshooting. I think you should write a book...entitled...."Off the Leash..Adventures in Vintage Audio repair"
Just another great video Tony! People can learn a lot on how to think thru the troubleshooting process watching this one (and many others). Very methodical , one step at a time, start simple, never assume anything. I'm an Electrical Engineer myself, about the same age as you and believe we share a certain radio hobby. But I went down the road of "0's" and "1's" not the "wavy bits" . Looking forward to the next one.
I have two of these amplifiers and and have had output transistor failures as well as problems with the protection circuit. One is a unit that I bought new in about 1972 and the other was assembled from a chassis and several power amp PC boards from an audio shop that was going out of business. One common problem was that there is a capacitor in the relay circuit that goes bad and at first the speaker relay just gets slower to pull in. but finally it just doesn't close. Replacing the cap fixes it. I have done that on both amps. The other one that I made from parts failed about a year ago and the relay became "fused" on one channel and I tried to repair it by cleaning the contacts. While it worked to some extent the affected channel would cut out because of poor contact. The problem was that no one makes a suitable replacement relay. I found an article on line that recommended a relay that would work, but you had to modify its internal wiring to match the footprint of the Marantz PCB. I was able to do that and bring the amp back to life. The relay was from Mouser, PN number MY2-02-DC24. it has to be modified to match the Marantz PCB and the footprint is a little small but I was able to make it work.
This is great, Tony. The 250 is an amp I always wanted to own but had heard that it was a bit twitchy and you are showing why that reputation exists. Really looking forward to Pt. 2. Please don't skip over any of your normal clean-up routines for those of us still learning this stuff.
I have an old 240 amp that I've repaired before. Same amp boards as the 250 but without the meters. I've seen it fail once where all of the outputs and drivers smoked...the board was charcoal! I had to find a "new" board on Ebay to get it working:). One challenge is even finding the correct output transistors anymore. Can't wait for part 2!
Great dianosis Tony. Must get my 1070 working again sometime soon, it has broken wires on the Thermisters from it being stuffed like a cushion with cat hair when I bought it. Looking forward to part 2.
Excellent project. I just finished my Marantz 500. I had never seen the inside of a 250 before, completely different beast. The 500 is an absolute pain to work on.
@@jeditoto3441 as of yet no, but I did an all out restoration on it. All electrolytics, new WIMA polypropylene throughout, all new output transistors, drivers and predrivers. Pretty much all new transistors in the whole input and driver circuit. Incredible amp. I’m working on my Phase Linear Dual 500 power amp right now and theyll have a showdown. Loser is being sold probably lol.
@@jeditoto3441 do you happen to have the device numbers from the schematic (QXX, etc) or better yet their actual device numbers? Depending on where they are in the circuit using high voltage device vs high current. Regardless I swapped the TO-66 for TO-220, which is a fairly popular option. Feeding one of the legs of the transistor can be a little tricky, but can easily be done. For the drivers and such I’m 99% certain I used MJE15034/MJE15035, otherwise the MJE15032/MJE15033 pair. If you get me device numbers I’ll look at the specs and tell you which one of the four to use. Figuring PNP vs NPN is easy of course.
@@xraytonyb , even lower power Marantz receivers invariably have 6 to 8 bad caps on a separate power-supply/protection-sense board that prevent the relay from closing. The voltage regulators and resistors bake the heck out of those caps and the shrink-wrap on the caps often shrinks back, exposing more of the metal can, or the guts of the cap expand and the bottom rubber plug pushes outward.
Nice and interesting fault finding, Tony! I have to this day not had problems with a light coat of lube on wirewound pots. I once used silicone lube, but this will break down if the wire heats (and turn into sand which would be very bad)!
really nice video Tony. The bigger brother to this model, the Marantz 500 was also a well known oscillator. Did not take much to get them going either.
Info for "newbies" and non-technicians: the screws holding the output transistors to the heatsink also make the electrical connection to the collectors (the metal case) of the transistors, which is why those screws need to be present, and tight; If they are loose, not only do you get intermittent electrical connection to the transistor but you lose the ability to transmit most of the transistor's heat efficiently to the heatsink. Marantz usually used white silicone heat sinking grease (and clear mica insulators) between transistor and heatsink to enable the transfer of heat, and I presume Tony wiped most of the white silicone off the transistors before he tested them with the multimeter. That grease is nasty, messy stuff; it absolutely ruins clothing and and it can be difficult to remove from painted or anodized metal surfaces. Make sure you have plenty of rags and paper towels handy, and alcohol or other solvents, if you have to deal with removing transistors from the heatsink. Clear heatsink grease is somewhat less messy but it doesn't transfer heat quite as well. Most modern equipment uses thin sheets of silicone as an insulator and heat-transfer medium in place of the mica insulators, and doesn't use/ doesn't strictly require heat sink grease. Whether the silicone pads truly work as well for heatsinking purposes without the addition of grease, I don't know. On old equipment I still use the grease even if I upgrade to silicone pads as insulators. I ways wear a shitty shirt and pants on such days, something already greasy and stained. PS, the metal mesh cages over the output transistors are to prevent accidental short circuits from the cases of the transistors, which have plus and minus voltages on them, to the chassis. Most transistor short circuits occur between emitter and collector anyway.
I use the fiberglas scratch brush almost daily; great tools, but they can be a little rough for cleaning wipers and commutator rings on pots (the stiffness of the fiberglass inserts varies depending on the source, some are softer then others). For pots, I use a pencil eraser instead (an ink eraser containg some kind of mild grit like silica or pumice is better, and usually safe for carbon tracks as well, if you use a light touch). A precaution for musicians: if you have gigs or practice sessions coming up, wear gloves when using the fiberglas scratch brush! Also smart to vacuum your work bench, and shake your clothing off outside; the glass fibers will drive you nuts for days if embedded in your fingers. Excellent tools, however; mine came from Esslingers (watch and jewelry supply). The German-made ones are refillable and better than the cheapo, non refillable, Indian-made scratchbrushes. They also sell steel, and brass, scratch brushes.
I would like to see how you go about ‘cleaning’ when it comes down to the years of dust & debris build up on the internal parts especially the pcb. I’m trying to learn how to rehab an old Pioneer sa-608 someone before me butchered. Love the videos!
Thumbs up done sir you show us the trouble shooting technique with the use of diff. test instruments more power to your channel tnx subscriber from the philippines
Hey Tony. I about to recap my vintage Kenwood KR5340 receiver. I’m not a novice I have several years of electrical / electronics experience and recently retired so I have time to take on projects like this. When you do a recap job is there a vendor you use that sells complete recap kits or do you use your on hand inventory when you take on a job like this. Thanks for all you do. It’s very informative. Sincerely Mark
Some bias circuits are wired in such a way that if the bias pot fails (the wiper losing connection being the commonest problem) the bias turns on full and the output stage draws excessive current, instead of throttling it back. Sometimes you can fix this by tieing the wiper to one end of the trimpot.
@@jeditoto3441 , I am not on audio karma, sorry. I haven't worked on this particular Marantz amp (I've worked on plenty of other old Marantz gear,, as well as old Pioneer, Kenwood, Sansui etc); but anyway,, you will note from the schematic (if it is indeed correct) that the bias trimpot appears to be used only as a variable resistor, and the third connection to the pot isn't being used. If the amp was in front of me, I would verify that the far end of the pot isn't tied to anything, and then I would measure the resistance setting on the trimpot as it is, and then adjust it so that the amp draws less current, and measure it to see if the resistance is now lower or higher. If *increasing* the resistance setting of the trimpot lowers the bias current draw of the amplifier, then you should tie the wiper to the unused end of the pot with a jumper. This way, if the connection to the wiper is intermittent and the wiper comes out of circuit, the resistance of the pot in the bias circuit will go to it's full value and tamp down the bias and the current draw of the amp. On the other hand, if decreasing the value of the trimpot increases bias current, fixing the design flaw might not be so easy or practical. In such a case, it's recommended to use a new, very high-guality trimpot.
@@jeditoto3441 , I did a little looking around on RU-vid and I found a 2 year old video from a guy whose channel I subscribed to only recently ---- " Electronics Old and New by M. Caldiera " ---- where he repaired a badly butchered Marantz 250 M. It's a 3 part series and in the first part he looks at the bias circuit schematic, which was done differently in the M version, with an extra resistor or two and wired in such a way that if the wiper lifted off of the trimpot the amp wouldn't go into full bias conduction.
@@jeditoto3441 , here's the link, if this channel allows. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-qaT-vZz66L4.html. The bias circuit and pot are shown at about ten minutes in. I don't know if it's applicable to the original 250 since this is the M version but it will give you some idea of the concepts involved.
Good find using the VOM. This reminds me to grab my dad's old Simpson from the basement. I know the high voltage battery was toast decades ago, but plan on trying to resurrect it. Maybe make up a DC power supply for it instead of battery.
A great video very interesting little failures but could you argue that the Fluke did find the problem as it showed too high volt drop for a germanium junction which in turn led you to try a different method of measurement ?...cheers.
The silicone diode has threshold voltage of 0.7V, whereas Germanium diode has 0.3V, don't you see a problem replacing one with the other? Thermal characteristics of the two diodes are quite different.
Great troubleshooting, as usual. Bravo, Maestro! Also curious, though, why you don’t replace with the germanium diode originally spec’d? What was in the other channel; G or Si?
When i saw the PCB with those blue Philips capacitors I instant thought they were suspect to one of the problems. Even new, unused ones of those models fail over time. I know, there were made over here in the Netherlands.😁
ThankYou xTb, just marvelous videos you make. Super-interesting as always. ,,,Extra interesting when speaking of the idea of 'fail-safe' diode-strings for the bias-line.. ..Enjoy the weeks for your company, fam&friends. Looking forward to, when you have time, for updates on the Amp. ,,br from norway.
Does this have the cascode JFET-BJT VAS like the 300DC? I pretty much refuse to service these anymore. Too many times I've spent hours going through the driver boards only to find a defective 2SK109 or mystery varistor.
(@10:12) - Yeah, Tony. Let’s discharge the bulbs - good idea; wouldn’t want the bulbs to shock anyone. I think you meant to discharge the capacitors. 😏
No zobel network I could see; a resistor with a few turns of wire and a capacitor wouldn't hurt I guess or just an RC HPF or two maybe to roll off at 35-45khz? Thanks again....DA.
Tony, you speak so slowly and deliberately that I usually run your videos at x 1.25 speed. Some other RU-vid channels I follow are hosted by people who speak so fast that I slow them down to x .75 ! It would be nice if the RU-vid software gave us a choice of less drastic speed graduations because both of those are a little coarse.
@@andrewcastellane7802 , thanks, I never noticed that option! [Edit: I just looked, and.... the reason I never noticed that option is because, on this Samsung phone anyway, it doesn't exist 😖].
Hi Tony Another great video! Does the marantz 500 have the same oscillation issues as the 250? At the beginning of the video, you have the tek576 in the background. Would love to see you use it🤗
Does it have output relay(s) ? If not, then it's doing what it's supposed to - running until it runs out of juice. DC offset is another, unrelated matter.
Does your amp delay the audio for a few seconds when it turns on, and then you hear a click from inside the amp, at which point the sound comes on? If the ound comes on immediately, without any delay or mechanical click, then the amp doesn't have output relays (unless perhaps it did, but somebody jumpered them out of circuit or removed them). It is possible to have a technician add delay and protection relays to the unit, and Tony did a video about this not long ago.
Thanks for the replies. No relays, so I guess it is the main cap discharging. Toshiba SA-202 C. Surprisingly excellent tuner. Better than the Sanyo JCX 2300k and the Pioneer SX-450. I often find them for less than $50 in various states of disrepair and bring them back to life. This one was an evening project .Detailing, replacing bulbs and cleaning switches and whatnot. In 9/10 physical condition. Great purchase for $15 bucks.
Tony, if you think your Marantz 250 has issues, wait 'til you see this video of a 250M repair posted several years ago by Electronics Old and New (M. Caldeira). ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-qaT-vZz66L4.html. Somebody really butchered it! He posted the repair process in three parts, this is part one.
Informative content!👍Thank you for sharing pal. Don't know if any custom PCBs you may need for upcoming amplifier? If so, we'd like to sponsor some free services( PCBs/ 3D printing/ CNC parts etc), and if possible, would love to achieve any collabs together!😊 (PCBWay)
completely wrong, sps1951 and sps1952 are definitely not darlington transistors, and the bias circuit with a germanium diode is always upgraded to a 250M scheme with 2 transistors for stability, 50 minutes of wasted time
