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F-1040 driver board in Sansui 5000a

G

gracep9

New Member
Hi all, I’m needing some help. I have a 5000a, and a f-1040 driver board repair/upgrade kit that I’ve been working thru. Before I started, it worked fine, but wanted to fix driver boards to ensure it stayed that way. Started with left, changed all caps, tested and all good. Then I replaced the transistor at TR801. Made sure the transistor was ECB correct according to the board which is lettering facing the opposite direction from original transistor. After this replacement I noticed audio much quieter, but still good on dim bulb. Thought is prob normal until bias is set. Proceeded with TR803/804, all good on dim bulb, still low volume. Proceeded to bias set. Bias showed .001 on meter and didn’t change no matter how I turned VR802. I’m guessing this and the low volume is related. I’ve double and triple checked, but don’t have enough experience to know exactly what’s wrong. I suspect something with TR801, but it does test ok. Any ideas?? Pics of board front and back. image.jpgimage.jpg
 
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gracep9 said:
Hi all, I’m needing some help. I have a 5000a, and a f-1040 driver board repair/upgrade kit that I’ve been working thru. Before I started, it worked fine, but wanted to fix driver boards to ensure it stayed that way. Started with left, changed all caps, tested and all good. Then I replaced the transistor at TR801. Made sure the transistor was ECB correct according to the board which is lettering facing the opposite direction from original transistor. After this replacement I noticed audio much quieter, but still good on dim bulb. Thought is prob normal until bias is set. Proceeded with TR803/804, all good on dim bulb, still low volume. Proceeded to bias set. Bias showed .001 on meter and didn’t change no matter how I turned VR802. I’m guessing this and the low volume is related. I’ve double and triple checked, but don’t have enough experience to know exactly what’s wrong. I suspect something with TR801, but it does test ok. Any ideas?? Pics of board front and back. View attachment 3657925View attachment 3657926
Click to expand...
If you used a ksc1845 for TR801 that will happen. Replace it with ksc1815.

Welcome to AK!
 
The transistor provided in the kit for TR801 is a C945 “pictured”. I found the issue with tuning bias. The board on the left that I’ve been working on is the “right” driver, thought it was left. When I moved the leads to the “right” fuse housing, bias worked. However, I now have no or almost no audio on right side now. Left side works, but the board for left side that I haven’t touched yet looks to be missing the Sony transistors at TR805 and one below it. (Not to mention the blown resistor). But that side is working currently.
 

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Actually I just did the board with that mod and it’s the one not working. The one with original transistors, blown resistor and the two missing transistors is the one that works, lol. I’m trying to figure out what I did wrong on the board I just updated.
 
gracep9 said:
The transistor provided in the kit for TR801 is a C945 “pictured”. I found the issue with tuning bias. The board on the left that I’ve been working on is the “right” driver, thought it was left. When I moved the leads to the “right” fuse housing, bias worked. However, I now have no or almost no audio on right side now. Left side works, but the board for left side that I haven’t touched yet looks to be missing the Sony transistors at TR805 and one below it. (Not to mention the blown resistor). But that side is working currently.
Click to expand...
Is it a KSC945 or a KSC945C? The 945C version has a center collector. The 945 does not.
 
I just got a 5000a. It looks like a modification was done to the underside of the board. Is this sufficient to make the receiver safe?
 

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You need to replace those black "chicklett" diodes with a pair of diodes in series (I use 1N4007). You also need to replace the input transistors (2SC458's) with 2SC1815's, and replace the bias pots. If you do those things, the boards should be quite reliable.
 
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