relax for a day
check again
mount back, wire
pray, turn On
if in doubt, insert temporary F2A5 in DC rails
Rebuilt mine and it is still smoking resistors, so back to the drawing board and time to replace even more of the active parts, rainy days are good
Final time I did replace all actives. Did find one dead that wasn't killed in the other channel. It (the other channel) came back easy. I think it was T7? Been a while! Hopefully that does it, and pads (or what's left of them) make sufficient connection with the legs of Q1 and Q2 and it comes back to life!
Russellc
Russellc
Is this just "best idea for least damage" or would this 2.5 amp fuse save Q1and Q2? Don't know if pads would go another desolder solder at those locations. If required, think I would cut Q1 and Q2 close to the body leaving the leg posts and solder to those...
Well, what ever you do, don't turn on phono pre (pearl 3) with everything powered up and pee set to phono! What was I thinking, first, not turning it on first, then not checking where selector set! Ouch!
Two tiny mushroom clouds!
Russellc
@Vunce = I believe it is R48. This is the SIT version.
I checked all of the active parts with simple DMM test and they all appear "not shorted" but clearly something is not healthy. I added the protection resistors but will need to dismantle again and start methodically removing parts and testing them / just replacing them.
Fortunately not short an amp or 2 to keep the music flowing.
..dB
I checked all of the active parts with simple DMM test and they all appear "not shorted" but clearly something is not healthy. I added the protection resistors but will need to dismantle again and start methodically removing parts and testing them / just replacing them.
Fortunately not short an amp or 2 to keep the music flowing.
..dB
Really good test rig 👍
Is that Aluminium square section that you use for the enclosure?
I have a few similar wirewound resistors that I would like to build something similar.
Do you have to insulate hardware? Does the hardware together with the resistors turn into some sort of transformer?
It was a big dummy moment, totally my fault. The power amp was 0n, so was preamp. Through carelessness on my part, I hadn't noticed the phono pre was selected on the preamp. Foolishly assuming it was set to mute, I flipped on the Pearl3 phone preamp. Apparently it let's off a stout transient upon fire up, but normally not a problem, as it should have been turned on first, then preamp, power Amp and so on.
Not only didn't do that, but didn't check if pre was set to mute. It wasn't. Worse it was on phono. I turned on Pearl3, a tremendous whack came over the speakers and two puffs of smoke coming from R25 locations.
Very embarrassing, hardly a cautionary tale, more like bull in China shop ! Fortunately, speakers are fine.
Russellc
Not only didn't do that, but didn't check if pre was set to mute. It wasn't. Worse it was on phono. I turned on Pearl3, a tremendous whack came over the speakers and two puffs of smoke coming from R25 locations.
Very embarrassing, hardly a cautionary tale, more like bull in China shop ! Fortunately, speakers are fine.
Russellc
Guys.. might have something interesting that will keep safe your amp in case of turn on thump.
Check here
Check here
Its just a painted wooden enclosure, it isolates well enough for low voltages
I built a similar one with Arcol 50w resistors on heatsinks. They dont need isolation. The mega wirewounds would need isolations if i threw 1000 volts on it but I dont. The four 120mm fans on each dummyload cools it very good, resistors just raises some 5-7 C over ambient under load.
Just tried XA252 repair. All set, slowly up with variac, when I got to 40 volts AC, (120 V a/c) led still had not come on, and stream of smoke
From R24. This is with every active replaced. Bummer.
Russellc
From R24. This is with every active replaced. Bummer.
Russellc
I did fire up the other repaired channel, all was good got good and toasty hot. A bit stumped now!
All I can think to try is too strip the board down with exception of the big resistors.
Clean inspect board, and while empty, clean it and re try continuity form what's left of pads to where ever they should be connected. I do believe at first I will cut off
Q1 and Q2 leaving the legs to solder to, assuming continuity is as it should be.
Then, remove from pucks and go through same protocol as before. It that fails, I will build new boards....waiting to see if they are available again from ZM
Really wanted this to go right, need this amp back in action pronto.
On positive note, now have boards and caps for PoP dual power supply conversion!
Russellc
All I can think to try is too strip the board down with exception of the big resistors.
Clean inspect board, and while empty, clean it and re try continuity form what's left of pads to where ever they should be connected. I do believe at first I will cut off
Q1 and Q2 leaving the legs to solder to, assuming continuity is as it should be.
Then, remove from pucks and go through same protocol as before. It that fails, I will build new boards....waiting to see if they are available again from ZM
Really wanted this to go right, need this amp back in action pronto.
On positive note, now have boards and caps for PoP dual power supply conversion!
Russellc
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