M25, M44, M50 all with some kind of problem.

[ImMrFist3r]

Ok I'm the new guy and have all sorts of mindless questions. A lesson learned is I should most likely stay away from eBay no matter how wonderful seller reviews are. So on to the problems that I have. I’m going to start with the worst here and go to my M50. I got it a little over a month ago and just got to test it out. Well not so good the left channel is dead and the guy I got it from is going to be of no help. I would like to think I can fix almost anything of a mechanical nature but when it comes to electronics I don’t have much of a clue.
Now I popped the top on the M50 (Rev. A) to find some wonderful but I don’t think life threatening stuff. I know the caps for the incoming power need to be changed and a 4th one added. But I took pics of the rest. 2 larger resistors that I need to know what the resistance is supposed to be and some smaller caps that look bad. The rail caps don’t look the best to me and some stuff under the heat sink looks like it got hot. Also there are 4 black things with holes in them (sorry no idea what they are) that look like they got hot on the back side of the board.





Ok so the M44 and M25 I have been using (they seem to be working great) but thought I should open them up and look at them to. The M44 (Rev.C) needs the same power in caps replaced. But it also has the large resistor (no idea of the value) and smaller cap problems. It also has a small resistor that looks like it got hot and a chunk of wire soldered to the back??




The M25 (Rev. G) also needs new caps but I’m not sure about the rail caps the coating looks like they also got hot.



I will try and get the heatsink off of the M50 tomorrow and get a pic of whats under there. So if you can please look at the pics I posted and let me know if I missed anything or need to check more stuff. I can also get better pics if they are needed just let me know what you think and what my best options for fixing my problems are.

[zeropoint0.5]

hi....

first of all i would not panic....the amps are perfectly repairable......

On the M50, you certainly have to replace both railcaps, the ps caps, the burned resistors between

the railcaps(330 ohm. replace with a 5W model and 1/2 inch away from the board) and all the caps with the isolation shrinked.

Under the heatsink you will find 4 burned resistors of 10 ohm/2w you can replaced.(had done this before once myself on a M50)

it is a typical thing.... only by seeing the condition of the railcaps this amp has been driven hard.......


On the M25 also replace the railcaps and ps caps and all the caps with the isolation shrinked.....


On the M44 the railcaps seems to look fine, you can replace them for sure (not nescessairy) replace the ps caps and all the little

caps with the isolation shrinked.... replace both resistors under the right blue railcap with a 5W model (91ohm), 1/2 inch away from the board.


These are typical issues for those amps..... probably there is more maybe damaged.....we don't know......

some components look burned/damaged, but the boards look all clean so after repair you shouldn't see anything any more.......


i suggest you contact Eric D or Valeks and send the amps to them for repair......


Depending on the price you paid, it's just, every old skool amp you buy (ebay or else) needs repair/service/bias and dc offset adjustment

and certainly cap replacement before you can enjoy them......

If you were my neighbour, i would help you, unfortunatly i'm not......


One advice !! Don't mess up the amps yourself first and bring them in after..... A technician loves to repair an amp (it's a challenge) but hates

to clean up the mess other people made.......


So Eric D or Valeks are the people to contact.... I hope they have time for you.......

[Eric D]

M50

As you know and stated, the input caps need to be changed. Even though the resistors are burned, and the small caps and 2 large rail caps have damaged heat shrink, all those parts probably work just fine. It is actually normal for the resistors to overheat, and the small caps to look bad. The damage to the large caps is a sign the amp was too hot, but these amps do run hot, so that happens to a lot of people. When I replace these parts, I put larger resistors in there, and lift them up off the board to keep the heat from causing more problems.

The real problem with this amp is that one channel does not work, and that could be a number of things. There are about 8 fusable resistors in each channel, and it seems that 75% of the time one of these is bad.

The dark spots on the back of the board are overheated resistors as well. I replace these and mount them touching the heatsink with some thermal paste to keep them cooler.

This amp could use new rail caps, but they are likely not bad, even though they look bad.

M44

That wire on the back is normal. I have seen that on many M44s. Same as the M50, this needs new input caps. The overheated resistors and messed up heat shrink on the small caps is typical of 95% of the M44s out there.

M25

It would be good to replace the rail caps, but they are likely not bad, despite looking bad. The input caps need to be replaced. This amp does not have as bad of heat problems as the M50 or M44 due from resistors cooking parts.

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My post is a lot of what zeropoint0.5 already posted, but I figure if you read it from two sources, it will just make you more confident in the information you are getting. He also makes a good point, if you are not good at fixing this stuff, don’t make it worse for the next guy who has to fix it. Right now those amps look like that have never been messed with, and that is the ideal condition for someone to work on them. I would not take the heatsink off the M50 (or any of them) unless you plan to fix it yourself.

[trickyricky]

Make it three, change the b+ filter caps (the dark blue caps ...usually 16 or 25v.. ) these have fail or will very soon.


I'm restoring 5 Zapcos and they all share the same b+ filter caps and all have leaked at one point...half of them had a lot of juice still on them. The electrolytic juice will eat up those copper traces and those will need to be repaired. So once you remove them make sure you check all traces underneath those caps...even below them as the juice flies through via holes.