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Accuphase E-202 repair and fixing mistakes

S

Saryrian86

New Member
Hello guys :) This is my first post on audiokarma and maybe one of the longest post i have written.
Backstory:
I got a job modifying a tube amplifier for a guy that live local to me. during the conversations over the phone about that amp about parts and etc , he told me about another amp that he had. A solid state one. A Accuphase E-202 that someone else had recapped for him a few years ago.
It had a issue with lower sound on one channel and after he got it home after the job was done the amp started to smoke right after he turned it on. He asked me if i could maybe look at it and see if i could find what the issue was.

im mostly into tube amp building and repairing so i was a little hesistant at first. I have tried to repair solid state amplifiers in the past and either have not figured out the problem or not found the real issue.
But i thought. I can't let a amplifier make a fool of me. I can do this! So i said i could look at it and maybe see if i can fix it

So this will be my first time trying to fix a solid state amplifier and get it really working again. This time i will not give up! And maybe with help from you guys i will reach my goal.

So back to the amp.

The owner told me where the smoke came from when he tried to fire it up. And that was around the power supply card area. And it blew a capacitor. The capacitor got swapped but the problem did not go away

The first thing i did was to check that all the electrolytic capacitors was mounted the correct way on the power supply card. And changed some of the old ones that the previous tech
did not swap out. And cleaned it real good. It showed that it had been warm over a long period of time from many years of use but nothing that looked really burned .a trace had been fixed Some point in time and Some resistors showed clues of been worn, but nothing stood out from everything else. I measured some of the resistors and changed the ones that had wandered to much in value with the correct values and watt size.

I even swaped out one of the transistors because it gave some odd measures.

Fired it up with a variac and took it slowly up in voltage. It did not take long before smoke started to appear again in the same area. I was not sure if it came from the card or from under it.
I shut the amp right of again. Ok.
That did not fix the issue. Lets see what got hot. I was to fast to shut it down so i could not find where the smoke came from. And i could not find one part that did go wrong at first glimse. Only clue i think was that one of the AC wires going to the 2 double diodes that delivers DC power to the power supply card looked a little like it could have been a little hot. So i soldered the two double diodes out and measured them with my multimeter. They measured good both of them. Ok.
Whats Next .

So i thought. Lets go through the power supply card part by part and see if i can find a issue.
So i did.
i may have found a issue im gonna investigate further. 2 of the 3 2sc1451 measured a little weird between base and emitter . And what i was told when i asked a little about thid was i needed to solder them out and then measure them so that the posibillity that the circuit around them could mess up my measuring is eliminated.
So my next step is to solder them out and measure them.if they still measure a little funky im gonna replace them.
Are the issue with those transistors big enough to have made the amp start letting out smoke or did i just found a issue that have not showed it self yet and the real problem are somewhere else still?


What do you guys think?
 
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One of the resistors that looked tired. Photo taken before it got swapped out
 

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I pulled out the 2sc1451 transistors now. Out of circuit they measured good . But i will swap them out anyway. I followed your adwise in the thread you made when you worked on your amp so i ordered plenty of KSC3503DSTU . so they are going in instead of the 2sc1451. Better safe than sorry :)
 
The capacitor that blew was in the place of the large one to the left . It has been swapped but the problem are still there. I finally found a better service manual on the amp than the one i had. With a circuit diagram on the amp .So hopes are getting up on getting this amp up and running again. :) so know i know what circuit the cap that blew was connected to. So im gonna trace down the connections to it tomorrow and see if i find something bad. If i remember correctly i think i did not hear any relay click after i turned the amp on either so. Alot to check tomorrow. :)
 

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Coincidentally, I happen to be into another E-202 currently. Perhaps this will be helpful:

http://www.wwdsltd.com/files/AccuphaseE-202RevisedSchematic1977.jpg
AccuphaseE-202RevisedSchematic1977.jpg
 
It is apparent that the power supply is among the weak links. It may be worthwhile to remove the driver boards, tone amp board, and filter amp board. At that point it might be safe to power the unit through a 60W dim bulb as a start, then move to a 100W dim bulb to achieve nearly line voltage. If that is successful, and you don't need to summon your local fire department, measure the voltages to and from the power supply/protection board (719-0004) to verify the proper ±55V main supplies and ±40V supplies. Don't be too surprised is the regulator transistors on the PS board get warm. They operate at about 150°F or slightly higher, which is NOT a great design, but not outside their capability. Also be aware that the heat sinks for those transistors are electrically live.

Solder connections on the PS/protection board can be suspicious, and several of the resistors also tend to run hot and eventually suffer heat damage, usually evidenced by blistered markings and cracked or missing external epoxy coating.
 
Thanks for posting the schematic. It was the same one i found right before you posted it after alot of google.

Today i started with swapping out all the 2SC1451 with KSC3503DSTU on all the cards. :)

Next up:
check the power connections and parts related with it, that are going to the power supply/protection board slot .

I think its there the main problem are located because it was there the capacitor that blew was connected, and it's in that area the smoke appeared too. And since the power supply/protection board did not have any big faults other than some resistors with heat damage and some that had drifted in value.
I think im getting closer to locating the problem.
 
Pulled out the small board where the 3 fuses are located. AHA. One was blown!. So now im gonna check all the connections and parts related to that fuse. Its connected to pin 2 and 3 on that board.
 

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Finnally i found a fault. I never been so happy finding a problem before . The capacitor that was put in instead of the one that blew was wired in the wrong way.
 
I swapped out the rectifier for the 39v. My gutfeeling made me do it and i suspected that some of the diodes was not healthy. Turned it on slowly. With only the powersupply/protection card in it. And increased the voltage in steps. Measured the voltages on the card and it the transistors worked without a problem. When i was almost at full voltage i heard the relay click. It wants to work. Finally. !
 
Then its back to testing with first with one main drive board and then two. I will check each card first to be sure nothing is wrong or way out of spec. :)
 
Tested with both main drive board in it now. Still no smoke and the relay still kicks inn and things are looking good. Soon ready for testing with speakers. And Adjusting bias and center voltage :)
 
Adjusted bias and center voltage. It finally it was time to test it.
It plays!!! And really nice too :rockon: when it plays really good on 5 dollar speakers from a cheap surround stereo setup i got for free. (My testbench speakers) the amp must play really really good on a pair of quality speakers . :D:D
 
FWIW, the flat grey film caps in those are not stable. I’ve found bad ones. Changing those out to some fresh poly film caps is a good thing to schedule.
 
I had this amp during the mid-late 70s. Very impressive performer, smooth sounds and yet very powerful when needed. Even the controls and switches felt rock solid. Never forget the extreme smoothness feel of the volume control and the clunk-clunk-clunk solid sound of the input selector that seemed to resonate throughout the insides. With the amp I was using a pair of home build loose copy of the Altec Model 15 enclosure, complete with 800 horns, tangerine drivers, and 421 woofers (although original woofer for that model was really the 416). At the time was working as the in-house tech at a Altec Pro store, so I got to keep all the faulty unrepairable speaker components that came in mostly damaged by overloads or falls during a concert etc. Also got plenty of diaphragms that only had the broken connecting flex strip and where easily fixed by scraping the ends and resoldering the strip at the breaking point. One day two 421 15" woofers came in where the magnet had somehow come loose and shifted to the point it completely crunched the voice coil, so the customer bought new woofers. I took them both apart, then used strong epoxy glue and recentered the magnets with a couple of stacked cardboard sheets the same we used to center the voice coil during reconing, let it sit for a couple of days and they came out as solid as new. Then installed complete new cones and voice coils that where always available at almost arms length in the stock room, and took them home. I did something similar with the tangerine drivers that where also damaged due to a fall in a concert. I used those speakers for years and never ever had any problem, and quite often would drive them quite hard during parties. The only thing is they lacked a bit on the high side, so I added a Motorola piezoelectric tweeter to each one mounted over one of the bass ports and that made it sound better (for the music of the time anyway - disco!). Best of all all the speaker spares where also free, I never had to pay for any of them, not even the 800 horns, they (the owners) would just tell me to take them home and enjoy, and the place was being run by them. I even got to use the showroom Teac C-1 Cassette deck which I think was the epitome of decks back then (except for the Nakamichi 700/1000) to record my tapes from vinyl. Those where good times!
 
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