Recondition of MS250 and M44

PGjunkie · Post by **PGjunkie** » Mon Jul 06, 2009 8:10 pm

Hi all, just register and this is my first post. Last weekend when I clean up my junk, I found my old lovers, a MS250 and M44, I open it up and found out there is rust at most of the transistor legs, some is even connected to each other. The caps look ok from naked eye, the board is clean, all other components look ok. I will clean the rust this weekend and fire it up to test if it is still working.
I think I want to recondition it or even modding, anyone got any recommendation?

bogart · Post by **bogart** » Mon Jul 06, 2009 8:18 pm

talk to eric d here on the forum...he is the man you will want to talk to about working on the 2250. M44s are easy to work on...great amp to begin on if you are just looking to swap the caps and fets...

PGjunkie · Post by **PGjunkie** » Mon Jul 06, 2009 8:34 pm

To clarify, I have the tiny MS250 (2x50Wrms) not the big arse MS2250.

bogart · Post by **bogart** » Mon Jul 06, 2009 8:42 pm

oops...I misread. That should be an easy one to...just about any of the regular phorum guys could do it I am sure...I just did all of my m amps myself. Still, Eric D is the man you should be talking too about it if you are looking for someone that does this for a living...

PGjunkie · Post by **PGjunkie** » Tue Jul 14, 2009 8:04 pm

I read through some older post about this topic and found quite a lot of information. I do this to MS250:
1. Check DC offset and found left output is 5.3mV and right is 0.5mV. There is a slight hiss on the left channel (more noticeable when the gain is 70% and more). Do I need to do anything about it?

2. Check all cap for leakage by slipping paper under the cap, no leak found, visually all ok. I counted total 26 caps on the board:
2200uf 16V 105c x3pcs
4700uf 35v 105c x2pcs
470uf 35v 105c x2pcs
10uf 35v 85c x13pcs
100uf 25v 85c x3pcs
33uf 16v ???c x3pcs

Should I change all or just the power cap (2200uf)?

3. I also notice there is a diode leg got trace of overheat.
Should I replace or just resolder?

Thanks.[/img]

Post by **Eric D** » Wed Jul 15, 2009 6:18 am

Can you post a photo of the board on your amp?

There are really only 5 capacitors to worry about. There are 4 big caps rated at 35V, the two smaller ones are what you need to worry about. Then there are 3 2,200uF caps rated at 16V, those are problems as well.

I would like to see a photo so I can get an idea what this corrosion you are talking about looks like.

Post by **Eric D** » Wed Jul 15, 2009 7:09 am

Here is a photo for a better idea. These 5 capacitors are what you need to pay careful attention too.

I just replaced the caps on 2 MS250 amps, and some of the caps on each amp showed signs of leaking.

PGjunkie · Post by **PGjunkie** » Wed Jul 15, 2009 8:14 am

Here is the pictures as attach.[/img]

bogart · Post by **bogart** » Wed Jul 15, 2009 8:18 am

well I see at least what looks like a burned resistor and the caps are a must in that amp.

looks like it has seen better days but shouldnt be a hard fix. good luck

PGjunkie · Post by **PGjunkie** » Wed Jul 15, 2009 8:26 am

bogart, it is a diode with lable D3.

I don't know what value is it. Can anyone tell me?

bogart · Post by **bogart** » Wed Jul 15, 2009 8:29 am

I am not sure...if you go to realmofexcursion...ampguts, you will be able to see what it was...they have pics of about every pg amp board

Yeah, I guess that the big d next to it would be indicative of it being a diode

PGjunkie · Post by **PGjunkie** » Wed Jul 15, 2009 8:43 am

Eric, your picture show different capacitance value. The 7 cap on your board is much higher than mine (470uf become 2700uf, 2200uf become 5600uf, 4700uf become 12000uf). Is there any reason you do that? What improvement? What other parts can 'upgrade'? Or this is a different model?

Post by **Eric D** » Wed Jul 15, 2009 3:08 pm

That diode is probably just fine. It may be bad, but it is pretty rare for them to fail.

There is no corrosion on D8, D9, etc, that is just solder flux and is totally normal.

Yes, it would be a very good idea to replace those caps. My photo has higher value ones because I just finished replacing them for a customer. The originals on this amp were leaking.

More capacitance keeps the amp fed more on a demanding input signal like a bass note. They don't make the amps sound better, but they keep it playing smoother if that makes any sense.

You could do some other upgrades like replacing the op-amps, but I highly suggest you stick with new caps and leave it at that. The amp will last a long time if you make this improvement to it.

PGjunkie · Post by **PGjunkie** » Wed Jul 15, 2009 3:25 pm

Eric, thanks for the explaination.
One more question, the hissing sound on the left channel can it be fix?

Post by **Eric D** » Wed Jul 15, 2009 3:31 pm

Swap your left and right RCA cables and see if the hissing sound moves to the other side.

If it does not move you may have a grounding issue with one of the RCA jacks on the amp. You could also have an issue with an output transistor.

PGjunkie · Post by **PGjunkie** » Thu Jul 16, 2009 4:25 am

Confirm it was my spare speaker problem not the amp. After I swap side of the speaker, right side got hissing.

Eric, the bigger capacitor cost is double or triple the price of original capacitance value. I am in the mid of planning the order.

Will update once it is done.

Thanks.

Post by **Eric D** » Thu Jul 16, 2009 6:30 am

If you swapped the speaker connections, and the hissing moved to the other speaker, then I would think your amp is the problem. Did you swap the speaker connections, or the RCA connections?

PGjunkie · Post by **PGjunkie** » Thu Jul 16, 2009 8:13 am

I swap the speaker connection.

PGjunkie · Post by **PGjunkie** » Thu Jul 16, 2009 8:44 am

Ok, to make it clearer:
- Hiss on the left speaker, I swap speaker from left to right, right speaker got hiss.
- Hiss on the right, I swap RCA, hissing still at right speaker.

Eric, where is the output transistor?

bogart · Post by **bogart** » Thu Jul 16, 2009 8:44 am

Hey Eric, what is causing the erosion of the enamel around that diode and a few other areas on that amp. It looks pretty bad in some area's...is that from electrolite coming off of those caps? Heat...I see it in older mono's that have been run really hot and show signs of several thermal abuse...an mmats 700d that I've been trying to repair for a while...It just keeps popping a signal cap and I can't locate shot ever else is causing it...but it has been battered from the looks of the transformer coil

PGjunkie · Post by **PGjunkie** » Sun Jul 26, 2009 6:02 am

Try to find the capacitor from locally, some are not available:
MS250:
Rail cap - couldn't find 12000uf, remain 4700uf at 35v (2pcs)
Power supply caps - 4700uf at 16v (4pcs) and 1200uf at 35v (2pcs)

M44:
Rail cap - 15000uf at 35v (2pcs)
Power supply caps - 4700uf at 16v (4pcs)

One question, I saw some default rail caps of the M44 you guy listed here is 10000uf at 40v http://phoenixphorum.com/m50-and-m44-advice-vt4213.html
Is there different batch from PG having better design?

Post by **Eric D** » Sun Jul 26, 2009 10:04 am

Diode D3 is part of the regulation for the power supply voltage. It can get pretty hot. My best guess is the heat is reacting with the solder flux and the electrolyte fluid from the capacitors to cause corrosion.

The 4 largest transistors are the output transistors. Two are used for each speaker output, one for the positive part of the signal, and one for the negative part.

PGjunkie · Post by **PGjunkie** » Sat Aug 08, 2009 11:42 am

Here is how I work on M44.