Sansui AU-555a repair help needed

[The Fuxtor]

Tested with headphones, DBT, & no power transistors. Sound was fine out of the left channel but the right channel was very staticky and poppy until it stopped making sound all together.

Me thinks you should replace those ufo style transistors on the driver board! There are a few threads on here that detail what some good replacements are. Remember to use that DBT afterwards!!

 

[avionic]

http://audiokarma.org/forums/index....recapped-sansui-au-555a.840764/#post-12037025

 

[bharry]

Hey guys, I'm back. I got a little busy and had to take a break but I finally got around to testing all the UFO transistors tonight. These are the results I ended up with. The 9002s are the TR809 & TR810 and the 8002s are the TR803, TR804, TR807, and the TR808. Once I unsoldered them from the board I was careless and they got mixed up some so I'm not sure which is which exactly. Next time I'll test them as I take them out.


9002-1C 120
.0L
.0L
.683
.684
.067

9002-1C 124
.0L
.0L
.662
.669
.0L


8002-1B 122
.613
.600
.0L
.0L
.0L

8002-1B 122
.640
.634
.0L
.0L
.0L

8002-1C 122
.0L
.625
.0L
.0L
.0L

8002-1C 122
.629
.622
.0L
.0L
.0L

 

[petehall347]

2 appear dead . 1 and five in list order .

 

[bharry]

So I should replace them all with the bolded ones found in this post (AU-555A recap list)? Are the three listed pretty much the same?

(4) CDC-8002
KSC2690A: KSC2690AYS
MJE350
BC639

(2) CDC-9002
KSA1220A: KSA1220AYS
MJE340
BC640

Is there anything else I should replace while I'm ordering stuff now?
Thanks,
Brian

 

[bharry]

The MJE340 & MJE350 are in-stock so I will probably go with those.

 

[petehall347]

it is always best to test everything to save on shipping

 

[slimecity]

Replace all the UFO's while you are at it. They are well past their expiry date and you will be happy with the results.

 

[The Fuxtor]

The CDC-8002 should use MJE340
The CDC-9002 should be MJE350

 

[bharry]

The new transistors came in today and as soon as got home from work I soldered them all in. Plugged my DBT into the wall and the amp into the DBT. Powered the amp on and the light stayed off! Brought the amp upstairs to my bedroom system, hooked it up to my turntable and speakers, turned it on, hit play on the turntable, and it works! Everything I heard about this amp appears to be true, I love the sound it produces and I'm going to be replacing my Marantz 1090 with it.

I'm so excited and grateful for everyone's help with this, thank you!

 

[The Fuxtor]

You will need to rebias the new transistors! Congrats!!

 

[slimecity]

Good work.

Keep at it - do the other mods and this amp will sound even better.

 

[kevzep]

The CDC-8002 should use MJE340
The CDC-9002 should be MJE350

Nope, the 340/350 are not good subs for those.

8002 = KSC2690AYS
9002 = KSA1220AYS

 

[bharry]

Nope, the 340/350 are not good subs for those.

8002 = KSC2690AYS
9002 = KSA1220AYS

Is it OK to leave them in there now that I've installed them?

 

[kevzep]

Is it OK to leave them in there now that I've installed them?

They wont hurt anything, but they are not a good substitute as far as performance goes. They don't even have a published spec for transition frequency for example so who knows what that is, and the gain varies widely from transistor to transistor....

At some point you might want to swap them out....but it will get you going for the time being.

 

[The Fuxtor]

Nope, the 340/350 are not good subs for those.

(4) CDC-8002
KSC2690A: KSC2690AYS
MJE350
BC639

(2) CDC-9002
KSA1220A: KSA1220AYS
MJE340
BC640

The info was wrong as far as the MJE Transistors are listed.... backwards! Which set is best ? I dunno....

 

[kevzep]

The info was wrong as far as the MJE Transistors are listed.... backwards! Which set is best ? I dunno....

Use the KSC2690/KSA1220.

the CDC8002 is a NPN, so the KSC2690.
the CDC9002 is a PNP, so the KSA1220

 

[thirelian]

OK, so you want to ensure your DMM is set to diode test mode - follow these instructions to do the 6-way test at the first part of this page and post your results here.

http://www.learnabout-electronics.org/transistor_faults_06.php

Yes, some of the MJ series will work as subs for your current outputs - but lets confirm they are OK first before replacing them

Hi slimecity, thanks for sharing this link- just what I've been looking for. I'm also repairing a 555a and just tested with the following results:
TEST 1 TEST 2 TEST 3 TEST 4 TEST 5 TEST 6
2SC1030#1 OL 26.2M 331.5K 248.3K OL OL
2SC1030#2 OL OL 334.1K 278.7K OL OL
2SC1030#3 OL OL 335.6K 288K OL OL
2SC1030#4 OL 8.06M 334.9K 261.2K OL OL

Based on failures of test 2 I guess I need to replace all anyway, but am wondering why my numbers are so off on tests 3 & 4. The link says results should be between 500 & 1K.
I used a Fluke 177 set to measure ohms, auto range. It that transistor fault or did I measure wrong?
Any recs on replacements? Seems AKers either like MJ21193 &4; MJ21196G...

Thanks,

Ian