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F-1040 driver board in Sansui 5000a

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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.
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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.
 
Hi folks,
I'm working on my F-1040-1 boards and wanted to confirm something @gracep9 wrote regarding TR801. I too noticed that the 2SC458 was oriented backwards compared with what the board lettering indicates. Will its replacement in fact be installed according to the lettering?

IMG_9467.jpg

And finally: Seems like the consensus that the part to use here is KSC1815, not KSC1845? I've seen much conflicting information on this count....
gracep9 said:
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.
Click to expand...
 
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That one is BCE so it's correct. The replacement will probably be ECB so it will face the other way. I haven't see a consensus on KSC1815 or 1845, I have used 1845 with no issues though.

Your post says "the consensus is" but then you say "you've seen much conflicting information." You can't have a consensus and "much conflicting information," right?
 
EastPoint said:
That one is BCE so it's correct. The replacement will probably be ECB so it will face the other way. I haven't see a consensus on KSC1815 or 1845, I have used 1845 with no issues though.

Your post says "the consensus is" but then you say "you've seen much conflicting information." You can't have a consensus and "much conflicting information," right?
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Ha! A fair point, yes. And funny: Every reference I've looked up on 2SC458 suggested ECB but.... Obviously I'll check the installed component, but...thank you!
 
Most of the 2SC458 transistors are BCE, but I have seen some that are ECB. There are both square and TO92 style 2SC458's out there. I have even seen some with gold plated leads. I typically replace them with 2SC1815's.
 
So, back with another troubleshooting question. I suspect this is going to take some gumshoe work on my part, but maybe one of you can set me on the right path.

I did the Skippy mod on my 1040-1 boards (the right one was shorted / blowing fuses). While I was at it I replaced all electrolytics and the 2SC458 with a KSC 1815. Powered up gently through a variac, all good, set center voltage and bias, all good. But the output from the right side--tried FM & phono--is significantly lower and tinnier than the left side, almost nothing. At full volume the output drops back down to nothing.

Traces all look good; no insufficiently soldered components. I had recapped other boards as well (EQ amp, tone board) but again: traces look good.

I'd previously checked the output transistors and they tested ok (at least, not catastrophically shorted). Our friend "the internet" suggests looking for an open / significantly drifted resistor on this board. Haven't turned anything up yet but will continue. I will naturally look at the 2sc756 driver as well; some sources suggest using KSC2690A instead.

Any guidance? I'd be grateful!
 
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Bruno Primas said:
Check to make sure the split bass and treble controls are set equally between the left and right channels.
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Thank you! Yup, wondered the same but that's not it. It's tonal but the volume drop is really significant. Maybe worsening since I first powered up?
 
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