MS2250 Repair (Burned Board)

Post by **bdubs767** » Mon Apr 23, 2007 5:47 pm

amazing....

fordtough1 · Post by **fordtough1** » Mon Apr 23, 2007 7:15 pm

Very freakin impressive.

I wish I had the patience and know how to do that stuff.

brenzbmr@sb · Post by **brenzbmr@sb** » Mon Apr 23, 2007 11:36 pm

you never seem to amaze me in what you pull out of your hat.

i didnt realize that was an original ms2250

good fricken job

email me about your update on the other project.

aloha

shaheen · Post by **shaheen** » Tue Apr 24, 2007 6:51 am

Doc , thats so amazing, I think thats the only thing that still worries me about my SOFAS , if I had to loose it in that way I would cry .

I have still not changed the caps on either the end. but I do not go to massive heat cycleson it, in fact my amp never gets warm to to the touch .

I play it like a girl I know

vin78 · Post by **vin78** » Tue Apr 24, 2007 8:34 am

Great work like always

Post by **smgreen20** » Tue Apr 24, 2007 4:41 pm

Yes, truely amazed. As you can tell, a lot of us admire your ability to do what you just did. I've got three amps that don't work (2 MTX amps, 1 Pioneer amp) and when time allows and I do some research on how EVERYTHING works, what does what, the order of things, the whole nine yards, I'll attempt it myself. Any where you know of that I can get started on reading/teaching myself how it all works? Again, great job.

Post by **Eric D** » Fri May 11, 2007 11:23 am

All finished, and ready to go. Board cleaned, and everything back in place. Just needs a new plexi panel for it.

Post by **stipud** » Fri May 11, 2007 11:53 am

I think my testicles finally descended.

Thank you Eric for that magnificent repair.

marko · Post by **marko** » Fri May 11, 2007 11:58 am

awsome job!! hows it sounding, say compared to the referance m25?

Post by **Francious70** » Fri May 11, 2007 11:59 am

I don't think I've ever seen a board repair look so natural. Way to go Eric, you got's dem skillz.

Post by **Eric D** » Fri May 11, 2007 3:42 pm

The amp sounds great, my only gripe is the output voltage is so high I need to invest in some new test equipment to test it!

I did not do a whole lot of critical listening, but the MS2250 clearly has more authority than the M25 does, and that is to be expected. With everything I have played on it, the speakers seem to be much happier having the additional control the MS2250 brings with it.

rolandk · Post by **rolandk** » Fri May 11, 2007 4:00 pm

Nice job! What type of insulators are you using for the output transistors? Hard to tell from the picture but if you're not using any you should put some in there. The original 2250's had a black anodized strip of aluminum, I wonder if there are any laying around here.

Post by **Eric D** » Fri May 11, 2007 5:18 pm

This amp relies on the anodizing of the heatsink to maintain electrical isolation. To my knowledge, only the newer TA amps, and the original MS1000 had the anodized strips in there.

This is also likely true, since no original MS2250s had clamp bars, and you pretty much need to use clamp bars with the aluminum strips, since there are no holes for the mounting screws through each device in the strips.

When I disassembled this amp, I found some damaged anodizing under one output transistor, so I stole a thermal pad off my parted out M50 and used it in this location.

So long as the amp never gets too hot, I would guess the anodizing will work just fine.

rolandk · Post by **rolandk** » Sat May 12, 2007 11:37 am

Up to you of course but relying on just the anodizing on the heatsink was determined to be insufficient and the strips were added. The original 2250's like yours didn't have hold down bars because the insulator strips had holes in them and the regular screws were used.

Post by **Eric D** » Sat May 12, 2007 1:09 pm

How did they determine it was insufficient? The ZX and ZPA amps use the same concept, and don’t seem to short out often.

Did PG include separate aluminum pads for each device, or were they indeed strips where multiple devices shared the same insulation?

Post by **smgreen20** » Sat May 12, 2007 6:30 pm

I have to say, fantastic job. It looks 100% original.

MW3 · Post by **MW3** » Sat May 12, 2007 7:10 pm

What a hack. Nice work...

Always a good idea to pick RolandK's brain.

He's knows everything there is to know about repairing PG amps.

brenzbmr@sb · Post by **brenzbmr@sb** » Sat May 12, 2007 7:31 pm

nice job man

oh i forgot to post in your flag pole(sorry to lazy to go back)
eric put it in senerio 3

it will look better and nice crib you have to..

roland. is there a possiblilty that i could get or purchase some of the
speaker and power blocks
for that syle of ms 2125(2250) front panel layout(if you have black better yet)

thanks

rolandk · Post by **rolandk** » Sat May 12, 2007 10:42 pm

Eric D wrote:How did they determine it was insufficient? The ZX and ZPA amps use the same concept, and don’t seem to short out often.

Did PG include separate aluminum pads for each device, or were they indeed strips where multiple devices shared the same insulation?

IIRC we did have some field failures where the back side of the output xstrs (collector) shorted to the heatsink and so the insulator strips were added. It was one long strip for each side ~6" long with holes drilled in them. You are correct that the ZX and ZPA amps used similar anodized heatsinks and had very few failures, I'm not sure why the problem with the 2250.
Anyways I'm off work this Monday but I'll snoop around Tuesday and see if I can find any of those insulators laying around. Theres about a 50/50 chance I'll find some.

rolandk · Post by **rolandk** » Sat May 12, 2007 10:50 pm

brenzbmr@sb wrote: roland. is there a possiblilty that i could get or purchase some of the
speaker and power blocks
for that syle of ms 2125(2250) front panel layout(if you have black better yet)

thanks

The old stuff is down to stems and seeds and I'm not sure what we have left. Phil would know if we have any.

skitz · Post by **skitz** » Sun May 13, 2007 12:44 am

nice work thats awsome ... and yeah it looks prity tidy too

how did that damage happen? fuse blow up or sumthing? or...?

Post by **Eric D** » Sun May 13, 2007 6:55 am

The damage is pretty much a natural occurrence on PG amps of this age. Their input capacitors short out and catch on fire. I have seen it on poorly taken care of amps, and on mint amps which I know were not abused in any way. These capacitors just have a short life span.

Roland, I have heard of so called “deep anodizing”, and since the plates on a ZX or ZPA are so thin, maybe the anodizing is much better. Due to the mass of a MS2250 heatsink, I suppose the anodizing may not take as well, which leaves the amp more vulnerable to shorting out.

Post by **VW337** » Sun May 13, 2007 11:32 am

Eric- Go get yourself some black RIT dye from the local hobby shop, craft store, or fabric place. Put a very high concentration of it in a throw away dish and mix per instructions. Remove your terminals and strip the metal from them, then let them soak in the mix over night.

The white/gray terminals just look funny.

eyesofra · Post by **eyesofra** » Sun May 13, 2007 12:10 pm

wow...that repair work looks like an art work done...amazing !!!!

rolandk · Post by **rolandk** » Tue May 15, 2007 8:52 am

Insulator strip status report: I looked around and couldn't find any of the 2250 insulators. Our service tech that would know of any secret stash is off this week and I'm going to China next week so it will be 2-3 weeks before we know for sure.