While I can appreciate MFJs commitment to the ham community, they are all to well known for "the occasional issue"...Peter, as usual your work is impeccable and it makes my day to see your videos Stay well and 73 Jeff de WD8JM
Great video!!!! As usual. MFJ is definitely a brand for those who aren't afraid to tinker. I don't believe they have a quality control department at all. I've taken apart more then a few MFJ pieces that where covered in flux or had cold solder joints, over soldered joints, solder bridges, and sometimes just totally missing parts.
Great video Peter, appreciate you sharing the thought processes behind it all. Rather watch your quality & informative videos than most broadcast TV these days. Keep up the awesome work!
Great video Peter and thanks for teaching us all this stuff. I remember having an MFJ ATU here 15 years ago, one of the coils was mounted to close to the metallic enclosure were it shorted!
I built a small AM receiver but could not find the needed inductors so I purchased magnet wire and rolled my own. Worked great. Thanks for the video Peter.
an excellent piece of logical deduction( electronic engineering), my 994brt works just fine but tempted to break the seals to inspect the inductors in the bias T. great work
I have the 998 rt and its been back to MFJ once. It works fine now. It's a very versatile tuner. I have the OG SGC and modded it to be able to use bias tee's. pretty easy.
I've got a MFJ 969 Versa Tuner II wit a roller inductor. However, it's only 300 watts. That tuner will tune anything including a bed spring. It even has an internal balun of 4:1 including a dummy load. I really like this tuner. Most all of my antennae are resonate so I don't really need an external tuner. The tuner in my Yaesu 991a will tune all my antennae. Sure do enjoy your videos. W Rusty Lane K9POW in eastern Tennessee
Wow, great work Peter. I thought you may have found the issue when you found the ground in the wrong place, but then to find that the coils were the real issue. Nice trouble shooting!
MFJ Made From Junk, I had a MFJ 100W tuner that I had to change variable capacitor so it would not arc at 10W capacitor plates way too close, Thank you Pete :-)
Thanks for the video. I would suggest to keep some ferrite cores for cases like this one. The ferrite choke you needed could be wound on FT114-43 core, 22+ turns of 0.9 mm enameled wire would do the job. 73s de R2AUK
Hmm, I've seen a similar fault, I think perhaps the short pulled too much current through the inductor and cooked off the lacquer inside, making it shorted turns.
Yes, if the center pins of the switch were grounded then any DC input voltage would haven been directly shorted to ground via the two inductors. They wouldn't have survived that for long.
I also had a MFJ-4117 where the inductor burnt up. Those bobbin style inductors have very fine wire and when they overheat turns short out. I replaced the inductor with JW Miller unit that had much larger wire, yet was not much larger, and fixed the problem.
Great video I have had one of these since they were released, the original one were even worse. No pcb board just three capacitors and the fibreglass box nevered sealed very. Mine is sat under the bench. 73 Richard M0UOO
Great Video..... very instructional!! Thank you! Have you found a way to change the factory default "Target SWR" ? The 998BRT has a mode button to accomplish this, but the 993BRT and 994BRT do not.......... it was never installed!
Another fine video,, but one question,,,,,, What did you do about the first problem with the DC input on the tuner that was not working right when you moved it ? Ron AC7RH
It's hard to fathom that MFJ would manufacture a Bias Tee with the wrong parts. But then, even persons working in the manufacturing field could have a bad day and choose the wrong part for insertion into the product. It seems to me that even in the manufacturing of Yaesu radios, a person could not use enough heat sync paste on parts which eventually burns out the finals. W Rusty Lane K9POW in eastern Tennessee
I missed a final conclusion: is a design issue? Were the values of the inductors wrong? I noticed you did have a schematics in front of you: was it from MFJ? Thank you for your excellent video.
I bought an MFJ DC distribution strip once and the main terminal binding posts were installed backwards - the RED was on negative and the Black was on positive. The soldering inside was horrible. I sent it back instead of trying to fix it.
It looks like the two chokes in the Bias-Tee only have one turn of wire. Why not just cut the shrink tube off of the 2 chokes, re-wind it with about 8-10 turns of magnet wire, and then put new big shrink tube back over, and re-install ? I just got a Bias-Tee today, and checked it. Both chokes I have in my Bias Tee are the exact same physical size as yours, but you can clearly see 8-10 turns of wire under the shrink tube. Each is about 51 uH, and about 105 uH together.
Could questions in my mind , the markings on the original chokes - if they may have been correct - but then shorted out & changed values - by the on/off SW. ? My quess that that small wire grounding the SW. may have been solder left by the worker installing the SW. , and it soldered to the ground plain - then when RF power applied - shorted the chokes - changing the values ? Thanks again John
That side of the switch was intentionally grounded. The PCB was wired so that the switch applies power when on, and ground when off. The weird wire/solder line wasn't doing anything. The problem was the wrong value inductors were used, and the unit was never tested.
My friend owned the ham store in Houston. They received product from MFJ that didn't work out of the box a lot. I recall he sold a G5RV wire antenna and it was returned because it didn't function. He gave it to a mutual friend. My friend opened it up and found the wires were never soldered from the factory. I got a 998 tuner brand new from him which didn't work out of the box. The quality from MFJ is not good. Mighty Fine Junk
The circuit didn't match the schematic. That switch was wired to ground the bias lead via the inductors when it was switched off, and to apply +12v when it was switched on. The pad that had that weird sliver of wire/solder was already connected to the ground plane on both sides of the board. That's why it was showing a dc short between the dc pass pin and ground when it was turned off - it was designed that way. You can follow the PCB traces at 36:58 and 26:12 . The invalid inductor values were the entire problem. Typical MFJ quality control. Did you go back and fix that intermittent power input connection on the tuner?
Hi Peter Excellent video as always. I have the same bias tee with exactly the same issue. Could you share the part number of the chokes you used in you repair. Thanks Adrian
@@TRXLab i didn't see you do it but did you put the center connections of those inductors back into the board and solder? or leave them soldered together off the board?
After reading some comments, I believe MFJ is not that bad at all. Few of the ones that makes Ham radio to still exist, with affordable equipment. The problem is the lack of a good quality control. There seems to be technicians with great experience, but also long time workers in the assembly line that are not technicians, but know the equipment they work on inside and out.
@@hectorpascal If you look at the pin that had the splash on it, 36:58 26:12 it has no traces running to it and is grounded to the ground plane on both sides of the board. The pin to the left of it is also grounded to the ground plane on both sides. It is designed to connect the bias wire through the inductors to DC ground when in the off position, and to +12V when in the on position.
@@stargazer7644 So the schematic at 22:15 was wrong!? Maybe! - since either C4 or C5 also seemed to be misplaced. But could this circuit change contribute to L1/L2 failure at switch off, due to discharge to ground of any high value DC feed line capacitors inside the tuner? Unlikely if the inductor coil wire is thick enough - since inductors impede transient current change, and I doubt the voltage rise would be significant.
@@TRXLab Nice to see you got it working. I was warned about these, but I'm pretty happy with mine. I mounted it up on a mast near the feedpoint of my dipole, and I've been using it to tune up on strange bands I can't otherwise use, like 90Meters. I have an amp, but I don't run power through it, mostly. I'm not sure how far I want to push it, really, since it's a pain to get to it if I burn it up.
Mighty fine junk. Martin's reputation is unchanged for decades. His firm has NO QA dept and it seems he hires kids off the street to perform soldering. Almost every piece of test equipment or gadget from MFJ is suspect. Have a screwdriver ready at all times. Also his designs for interfaces were great.... In 1972... Who uses DiN connectors for keyboards? The SWR analyzers use 10 AS batteries and you can blow a diode just by turning it on if the UHF button is pushed in. A known issue for decades.
Would have lied to have seen an 'autopsy' of the iniductors. They might have been ruined by excessive RF power applied to the unit which may also have melted the solder connection on the switch.
I am sorry for saying this but MFJ got worse and worse over the years. I saw very often corrosion inside because of bad seals, sometimes after only 2-3 years. I think that this failure is so unique, i would sent a notice to MFJ. That has nothing ti do with warranty, that is a thing of them believing in their own products. They could proof it by sending a brandnew BIAS unit. Peter, another good investigation comes to and good end, well done, great vid! 73 de Olaf
Unfortunately the number is not readable but it is a muRata and taking your number it makes sense inductivity: 47 uH max (DC): 1.65 A max resitor: 55 mOhms you can use it...
@@TRXLab Hi Peter, I have used my DE-5000 to test the two 18473C in series and it reads 3.2 uH. I lifted one leg on each choke to test. I removed both and tested each. One is 2.6uH and the other reads .023 ohms but no inductance. Using formula 14Mhz * 6.28*3.2uH I get 282 ohms impedance. I think that is the reason it does not work. WJ3U
@@TRXLab Hi Peter, I also checked the muRata website and it does list the 18473C as 47uH. Must be a mislabeled batch. I found some axial 100uH chokes that should work and ordered them.
I always do a shake test on all MFJ items new out of the box before powering them up. There's usually one or more items loose rattling around inside. Their QA is a joke. Opening them up and looking for obvious problems is always a good idea.
That DC blocking circuit in the tuner looks like it was fitted, as the unit did not have that option fitted as new. I would be very suprised if that was a factory mod. workmanship was just to bad. I never trust any unit that shows signs of people being in there before. nice fix
Good morning, great videos as always. I have sent you an email regarding a Icom7800 that belongs to a family member in Denmark. Kind regards vk3ajk - Melbourne , Australia
Diese kleine Metallklammer wird beim MFJ-4116 als Brücke anstelle des Schalters benutzt, ich habe heute nämlich einen SG-230 mit so einer Platine versehen, ist absolut identisch nur ohne Schalter. Was die Verarbeitung vor allem die Löt Qualität angeht, absolut unterirdisch. Ich habe alles nachlöten müssen. Ich vermute hier wurde eine Platine benutzt die für einen 4116 vorgesehen war und beim Schalter einbauen ist die zuvor entfernte Drahtbrücke irgendwie mit eingearbeitet worden. Hauptsache der kleine rote Quali-Aufkleber war mit Handzeichen versehen aufgeklebt. Was die Spulen angeht, sind bei mir die gleichen verbaut, ich habe keine SWR Probleme. Ich habe sie allerdings auch nicht gemessen. This small metal clip is used as a bridge instead of the switch on the MFJ-4116, because today I have equipped an SG-230 with such a circuit board, it is absolutely identical only without a switch. As far as the workmanship is concerned, especially the soldering quality, absolutely underground. I had to re-solder everything. I suspect a circuit board was used here that was intended for a 4116 and when installing the switch, the wire bridge that was removed earlier was somehow incorporated. The main thing was that the small red quality sticker was affixed with hand signals. As far as the coils are concerned, I have the same built in, I have no SWR problems. I didn't measure them either.
@@TRXLab Ich meine diesen kleinen gebogenen Draht, der den Kurzschluss verursacht hat. Schade dass ich hier kein Bild reinstellen kann, habe Fotos davon.
MFJ is known for poor quality parts and poor quality workmanship. They are a low budget manufacturer for sure. If that tuner is rated for 600 watts RF I would worry that those inductors you put in can handle that level of power. I would take off the heat shrink from the original chokes and look for any damage to the windings from overheating. Was there any inductance value marked on those original chokes?
I’m sorry I’m Normally the most patient fellow in the world but this video I’m sorry it took waaaaaaaayyyyyyy to long for your explanation of a very substandard device. Yes I was thrilled to see a possible dry joint and a short to earth I had seen this in the first nano second and yes your a proud American (maybe from my Oma’s place originally) And yes you have impressive Radio Shack with every possible test device. But do you have 4X1000 or an 807? Anyway it was interesting for the first ten minutes. I know your proud but I have ADD and I almost necked myself. I don’t want you to change your ways but I am trying to be honest.
MFJ = Junk. None existent quality control. The chokes were cooked by the big ugly short to ground. Given the size of the cores I would have been tempted to rewind the chokes by hand. Karl
