Sansui 8080db - Power Supply board (F-2656) issues

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anti-doom

Well-Known Member
Hi All,

I need to start over again starting from PS board (F-2656) since my 8080db is having a many issues such as sratchy noisy FM, popping and loud noise pop from speakers when switching from FM to Phono. Once in Phono, it has loud hum on both channels. Previously, R07 resistor (4.7 Ohm) was open. Then I replaced that resistor and recapped entire board and replaced all 3 transistors (Tr1 with KSC2383, Tr2 with KSA1220, and Tr4 with KSC2383). Tr3 is till original and tested good.

I measured all the voltages following the schematic and found some voltages are within the schematic and voltages on regulated section (green box) are out of schematic. Look at the attached images for my measurement reading in red color compared with the schematic in orange circles. For example, at pin 15 which go to EQ board, it should be 38V but I got 52V.

Now interesting about the Tr4 (KSC 2383). Originally, it was 2SC1211 (was open) and was installed opposite to the ECB printed on the board. When I put new 2383 in follow the ECB pinout on the board, I could not get 12V out of B pin (per schematic) and sound is distored on both channel. I also goe 22V at pin 15.

Then I flipped Tr4 (as it is in the attached image), then I can get 12V but pin 15 is 52V which is too high.

Here are my questions :

1. Should I keep Tr4 as it is right now as I read somewhere that ECB printed on the board is wrong. Or should I reverse it back to ECB on th eboard?

2. Should I replace Tr3 (big can 2SD315) transistor although it is tested good?

3. The collector of Tr3 suppose to have 41V but 53V is there? Is there something wrong.

If you have a working 8080db, could you please to measure the voltages of regulated section (green box) of your F-2656 board and let me know what is wrong on my board.

I have removed all the resistors, transistors to test them while out of the circuit and they are tested good. Also double checked the polarities of the new caps. They are all good compared with original caps. So kind of loss now.

Please help me to figure out the issues here.

Thank a lot.

BTW, AS OF NOW, THE RECEIVER WORKS FINE ON AUX INPUT. IT ACTUALLY SOUNDS EXCELLENT BUT IT HAS ISSUES ON FM AND PHONO AS AS DESCRIBED ABOVE.

8080 ps board.PNG
 
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check your work and see if you accidentely bridged some connections near T1, T2, T3. From the voltage readings it seems as if T3 is shorted. Check ZD01 for short/open. That 38v feeds the requlator for AM/FM on that small board on the tuner assembly. If you were feeding it 52v instead of 38V, that requlator supply could be hosed as well. That 38v from the power supply board also feeds the equalizer, which could be damaged from the 52 volts as well. Disconnect the wire on pin 15 of the regulator board, and keep off until you have resolved the power supply issue. As far as transistor lead placement, you should be following the schematic instead of the printing on the board. TR04 collector goes to the base of TR03. TR04 Base goes to R08 (1K ohm). TR04 Emitter goes to the cathode of ZD01, and resistor R09 (8.2K) . Do the same analysis for TR03 as you may need to use a TO220 transistor because 2SD315 are no longer available (If TR03 is indeed shorted or leaky.
 
Tom,
Thanks for the input. I double check my work again and no bridged solder or connections. All look good. I replaced ZD1 with 1N5243B. Also just disconnect all the wires from PS board to EQ board before I fix this high voltage issue. Please look at this image and let me know what you think. The TR4 (KSC2383) is now installed opposite to the schematic and printings on the board. If I install it according to the schematic (as your recommendation), I would not get 12V out of TR4 Base after R08 resistor. I already removed TR3 and TR4 out of the board. What you think?

Thanks.

IMG_1882.JPG
 
anti-doom said:
Tom,
Thanks for the input. I double check my work again and no bridged solder or connections. All look good. I replaced ZD1 with 1N5243B. Also just disconnect all the wires from PS board to EQ board before I fix this high voltage issue. Please look at this image and let me know what you think. The TR4 (KSC2383) is now installed opposite to the schematic and printings on the board. If I install it according to the schematic (as your recommendation), I would not get 12V out of TR4 Base after R08 resistor. I already removed TR3 and TR4 out of the board. What you think?

Thanks.

View attachment 1820171
Click to expand...
The board silkscreen is correct for TR4.
Also you still need to replace those three 1 ohm fusistors before the fuses.

And those 4.7uF rail capacitors can be polar. Not sure why Sansui made them non, because they're tied to B+/- and then ground, if those ever reverse polarity there's a much bigger issue.
 
TR04 needs to be installed according to the schematic. Disregard the 12v reading for now, and this is not important as the 38v. I would pull that 2SD315, and install a TO220 NPN for the time being to see if you get the voltage at pin 15 to drop to 38v
 
Tom B said:
TR04 needs to be installed according to the schematic. Disregard the 12v reading for now, and this is not important as the 38v. I would pull that 2SD315, and install a TO220 NPN for the time being to see if you get the voltage at pin 15 to drop to 38v
Click to expand...

Got it. Will do it today. Thanks
 
ivandezande said:
The board silkscreen is correct for TR4.
Also you still need to replace those three 1 ohm fusistors before the fuses.

And those 4.7uF rail capacitors can be polar. Not sure why Sansui made them non, because they're tied to B+/- and then ground, if those ever reverse polarity there's a much bigger issue.
Click to expand...

I replaced those 4.7uF rail caps with new bipolar ones same value. Should I change to polar caps or just keep them there? Thanks.
 
Hi,

Originally before I recapped the PS board, voltage at pin 15 was 47V which was higher than 38V per schematic. Then, I recapped the whole board and changed TR4 (2SC1211 to KSC2383) and ZD01 to 1N5243B as well as some resistors that were open. After that, I got voltage readings in RED color which were way to high and off from schematic.

Then I :

1. Remove the 1N5243B (ZD1) and put back the original ZD1 (EQA01-13R)
2. Put new 2SD315 in which I got from another 8080db

Now the voltage at pin 15 dropped from 52V to 47V which is back to it was before recap but still higher than 38V as it should be if schematic is not wrong..

But I have a question. Schematic shows voltage going into C leg of TR3 (2SD315) is 44V and out at E leg is 38V. But voltage across R01 (big white wirewound resistor 10 Ohm 3 W) is 53V which goes to C leg of TR3 so voltage out at E leg is 47V which makes sense to me.

Any though?

Please look at attached image fore detail.

BTW, the receiver is working fine now and sound good.

It still has loud pop noise thru the speakers when switching from FM to Phono and loud hum follow volume while in Phono but I wtill take care of this later. Focus on the power supply for now to make sure it is correct.

8080 ps board.PNG
 
Or maybe R01 (10 Ohm 3 W) resistor is open. I check and it is good. Measured 10 Ohm across it.
I need 38V at pin 15 to feed EQ board and 44V at pin 18 to feed F-2619 (PS board for RF) for tuner section.
Right now I got 47V and 52V respectively.

Or Should I increase value R01 to drop voltage from 55V before R01 to somewhere 44V after R01.

Please help me.
Thanks.


8080-2656 3.PNG
 
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Yes it is 8080db and the voltages on schematic at pin 18 and pin 15 are wrong. They are supposed to be ~53V at pin 18 and ~46V at pin 15. That info is confirmed by some AKers. Thanks.
 
anti-doom said:
Yes it is 8080db and the voltages on schematic at pin 18 and pin 15 are wrong. They are supposed to be ~53V at pin 18 and ~46V at pin 15. That info is confirmed by some AKers. Thanks.
Click to expand...

Working on an 8080DB, thank you for the voltage clarification. I spent way too much time trying to figure out why I was high at 15.
 
milo63 said:
Working on an 8080DB, thank you for the voltage clarification. I spent way too much time trying to figure out why I was high at 15.
Click to expand...

Yes, I have spent couple weeks to figure out why so high until someone here on AK told me that the schematic is wrong.
 
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