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Sansui AU-9500 Driver Card F-2029-1 bad

vuman

vuman

New Member
Hello Team,

I need you help to identify the issue in one of my F-2029-1 driver card that when bad after upgrade capacitors and transistors.

I upgraded in two stages, first all power capacitors on F-2030-1, F-2019, and F-2029-1. All worked well and the sound improved substantially.

Then, recently I got more parts with KSA992 and more capacitors for F-2019 preamp. After replaced capacitors and transistors, the relay will not kick in.

I identified one of the F-2029-1 went bad, I swap the two cards from L to R and R to L. With one good card alone, the relay kicked in, if plug in the bad card, the relay will not click.

In troubleshooting,
- I took out all transistors and tested NPN, PNP, they are all good.
- TR801/803 were replaced with KSA992
- VR801/803 were replaced with bourns cermet 5K and 200ohm respectedly
- replaced C801 with same value 2.2uf 50v
- replaced C815/817 with 220uf 80v
- replaced C807 with 220uf 16v BP
- took out 2SA483 PNP tested good
- took out 2SC783 NPN tested good
- took out 2SA706 PNP tested good
- took out 2SC1124 NPN tested good
- took out 2SC983 NPN tested good

What else can I check, please help to identify the issue. I am greatly appreciate.

Thanks

F-2029-1.JPG
 
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Why did you replace the transistors? Were they bad?

Something had not been mounted correctly, I would suspect the pinout of the transistors could be different, all the original ones are probably centre collectors whereas the new ones are most likely not...
 
Hello Kepzep,
I replaced the transistor because one of the channel dropped out occasionally. Also the transistor CSA726 was replaced as recommended by members.

The pinout was match correctly as the new KSA992 is ECB while the old one CSA726 is BCE. So the E from KSA went to E on the E mark on the card, so on so forth. I also trace the route on the back of the card. The KSA992 has center collector.

Thanks
 
Sadly pulling and testing transistors doesn't always work. Some will test fine until put under an actual working load. Lower gain may indicate something isn't right but no guarantees there either.
 
There is an unpleasant looking solder blob on the topside of the board at one end of a resistor on the right, (pitched up in the air), are we sure that blob hasn't pierced the end cap of the adjacent resistor causing a short?
 
Yes, that is R845, it's a thermal protection that not needed, I remove the thermal fuse and temporary re-used the register. I did measure the registor on PC board and show good value.
 
The schematic should indicate voltage values at various points on the board. Take some measurements and see where it varies from the established values.

- Pete
 
I found the issue with the bad card. The cap C815 was lose, I re-solder it and the relay kick in nicely.
There is another problem, the bias voltage are high for both channel, 43mv and 480mv respectively. Measure the DC offset at post 3 and 4 on F-2030 reflected the same value 43mv and 480mv. I did try to adjust VR801 but not successful. Please advise.

Thanks
 
I am curious to why you are using a NP cap for a bypass rather then what is called in the schematic? And why did you use a 220uf instead of the OEM recommended 47uf for c815 and c817?

-Warren
 
vuman said:
There is another problem, the bias voltage are high for both channel, 43mv and 480mv respectively. Measure the DC offset at post 3 and 4 on F-2030 reflected the same value 43mv and 480mv. I did try to adjust VR801 but not successful. Please advise.

Thanks
Click to expand...

Were the KSA992 replacements for the differential pair hFE matched?
 
Hello Lee,

Thanks for your question. Yes, I replaced KSA992 for differential pair hFE matched. In fact, I replaced them twice. Still, one of the bias voltage of 43mv and 480mv.
When I try to adjust the bias at VR801, not much changes.
 
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Really weird, tonight, I replaced the NP Nichicon muse 220uF 16V with my original but new Elna Cerafine 220uF 10V, and also the C815 and C817 with also Elna Cerafine 47uF 100V. The bias voltage is now between 16 - 17mv on both sides. I think the amp is working now. I may monitor it couple days.

IMG_0991.JPG


Thank you for all your supported. It is a great site to hang around.
 
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