Restoring a "mighty" AU X1 / output transistor replacements

I pointed out the 11000 as an example, since I didn't have the AU-X1 scat. Grabbed it for a look-see, and yes, there's C30 on the amp board, and C01 & C02 on the relay board. All are 0.047uf. These caps are there to provide stability at high frequencies, and as such are reasonably important in something like the X1.

Suggestions:
Polyprop: http://www.digikey.com/product-deta...ronic-components/ECW-F4473JL/P12076-ND/585143

Smaller Polyester: http://www.digikey.com/product-detail/en/panasonic-electronic-components/ECQ-E2473KF/EF2473-ND/56444

There are a few Polyester that are smaller, but I worry about their current-carrying capability in case of instability. The two listed here are good choices, and are pretty close in size, so if the slightly larger Polypropylene isn't a problem, I'd use it.

But either is miles better than the Sansui 'greenies'.
 
Hi EW, i don't have Sansui 'greenies' at position C01 and C02, but i will replace them anyway, thx for pointing us in that direction.

regards
 
Both power amp modules are back in the chassis now, both with original Sankens. DC and bias can be set to the desired level. This is the first time i connected both channels to the scope simultaneously and i noticed that there the output of one channel is almost half of the other channel. It seems to originate from the pre amp and i will post some measurements soon.
No signs of oscillations though and so far i am happy with the results. Tomorrow i will feed the signal direct into the power amp

Regards
 
I noticed the same...lived with it.

(Correction)
Oooops...
noticed that there the output of one channel is almost half of the other channel.
Click to expand...

Read that part differently.

My X1 did not have different output levels...in as far as I could measure.

Read and replied initially in haste.
 
Last edited:
I noticed that the balancing of the volume pot is not correct anymore, or never really was. I adjusted a bit with the separate left and rigth adjustment and both channels supply the same power.Clipping starts at ~37Volts using a sine wave.

Here you see a 40khz at 21V rms at the output, both channels driven simoultaneously:image.jpg

I will do some last stabiliteit checks, finish the wire routing and put everything back together. After that final bias and DC adjustments
 
Great work there Harold. Bravo!

Any details you can share regarding how you discovered and repaired the grounding problem?
 
Hi Ron, in the end it was just a bad ground wire connection, caused by the breaking of the connector. Nothing special
 
Harolda said:
Here you see a 40khz at 21V rms at the output, both channels driven simoultaneously:
Click to expand...
Do be careful running large-amplitude square waves at high frequency. This sends a lot of energy to the Boucherot cell we were discussing here. Often times, when doing something like this, it'd not be too uncommon to see the resistors start to smoke.

Square-wave testing is fine, but I'd limit the peak-to-peak voltages to perhaps 20 or 30V. And I'd check those resistors for proper value and for any signs of overheating.
 
Thx EW for pointing that out, i am glad to learn from the experts. I will perform a check of all components on that speaker relay board. The Panasonic ECw caps are already en route. The relays have been replaced about 3 years ago, so i expect no issues there but i will check the Large 7W resistors on that board as well.

I don't know yet what to do about the volume control. It has been dismantled, fully cleaned and reassembled. i also checked the position of the wipers before fixing everything.
 
Harolda said:
i noticed that there the output of one channel is almost half of the other channel. It seems to originate from the pre amp and i will post some measurements soon.
Regards
Click to expand...

Might not be the same case, but in a 7070 I was restoring, there was very low volume on the L channel vs the R. Boiled down to me NOT making a solder bridge that was needed after replacing a cap. Once that bridge was made, voltage came right in line and corresponding volume level was corrected. Starting at post #46, finally discovered by post #80.

http://www.audiokarma.org/forums/index.php?threads/7070-restoration.700459/page-3
 
jheu02 said:
Might not be the same case, but in a 7070 I was restoring, there was very low volume on the L channel vs the R. Boiled down to me NOT making a solder bridge that was needed after replacing a cap. Once that bridge was made, voltage came right in line and corresponding volume level was corrected. Starting at post #46, finally discovered by post #80.

http://www.audiokarma.org/forums/index.php?threads/7070-restoration.700459/page-3
Click to expand...

hi John,

the volume difference is not present at low levels but the difference increases to higher volume pot settings. I did some listening tests yesterday and it can be adjusted by a small turn of the power amp channel attenuators. The amp ran for a whole day also at higher levels and no issues at all and it is really amazing.

Dr*audio helped me on how to perform stability checks, i will do that after the relay board has been checked and new film capacitors have been placed on that board, like EW advised.
 
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