Sansui 9090db green protector light, no output

Just be careful if you decide to replace the diodes. One is a 24v Zener, and another is a dual diode. I usually only replace diodes if they are bad, but others feel they can be replaced if you are already working on the board. I try to limit the qty of new components being installed to get the unit working, and then make the decision to replace other parts as part of a complete restoration.
 
All 2SD and 2SB transistors measure consistent at .49-.51v on the diode test with no faults. I removed yellow legs from power supply and R30 and R31 both show open...

TR01 tests good, TR02 fails reverse polarity test base to collector
 
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So I replaced R30 and R31 on power supply board, powered on through DBT, immediately saw that the signal strength meter on the tuner had returned. Hooked up some throw away speakers and had sound both channels. Shut her down and waiting on replacement transistors. Do you guys suggest adding fuses in place of the resistors @ R30 and R31 like the later models?
 
Hey Guys, back at it with everything I need to rebuild power supply and driver boards. Still chasing down voltage issues at the board itself and noticed the outlets on the back are only reading 97v...

I've verified 123v going in and I'm working through the schematic to isolate anything in between. My voltage tests are being performed w/ DBT and without the driver board installed- relay clicks and green protector light on.

Connections look ok at the outlets, the universal voltage selector is in the 120v position, some voltages at the board itself are ok, others are low by a few volts

Any thoughts on the low voltage at the outlets?
 
I removed all secondary legs from power supply board to isolate transformer, still getting 97v even straight to the wall (no DBT). Opened the power switch found lots of carbon on the contacts, I swapped the unused spring loaded contact from the idle side to the working side, powered back on and had 122v at the switched outlet.

I installed all secondary feeds back to power board, installed the driver board, powered on, came out of protection (green light), then the 10a fuses at F01 and F02 popped. Powered down, noticed straight away a lot of heat at TR702, 704, 706 and 708 (which correlates with the side of the driver board I've been working on).

I only replace the components which tested bad on the driver board, several out of spec resistors, TR18, R66 (1k ohm which was fried), and TR14. I was hoping get the unit working before recapping and replacing all transistors.

I'm going to go through my work one more time but if theres anywhere you guys think I should look?

Thanks
Paul
 
1. Keep working with the DBT connected.
2. Disconnect Driver Board (F2624)
3. Please let us know what voltages are you reading here:

upload_2018-8-1_22-30-27.png

4. Give us pictures of F-2624 and F2656 with the best resolution possible.
5. Are the outputs and emitter resistors OK?
 
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Testing some components on driver board this pic...installed board was complete. I measured diode, volt and ohm at all components along with the mirror side. All readings were close. I lost TR702-708, actually the top two are ok, it toasted the bottom transistors before the 10a fuse opened and top ones test ok. I can see why the 6a fuse is a good idea.
 
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Where you have "43.3V" labelled - something is pulling the voltage down. As it is right after the main rectifiers the most likely culprit is the 1Ω current limiting resistor R30? connected to pin 04, maybe stressed and gone high resistance. Measure its resistance (with power off) and see what you get? - compare it to R31 which seems OK. ;)

If you find R30 to be faulty I would replace both.
 
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1 ohm resistors @ R30 and R31 test good. Do I have to pull D01 and D02 for proper testing?

Secondary legs unplugged from 2656 = 121v at switched outlet
Secondary legs plugged into 2656 = 97v @ switched outlet

If the transformer is only getting 97v on DBT then it makes sense all my measures are low?

I'm sure the main caps are the big draw but seems like it should come back up after they are charged?

Ground issue maybe?

Can I reintroduce secondary legs to one isolated section at a time to see if measurements change? (ie, just brown, just yellow, etc)

I'd leave Gray and White installed for reference to ground.
 
Replaced R30 and R31 just to be sure, voltage came up from "43.3V" to 45.5v at +C03

So the voltage drop at the transformer and all my measure points is approx 20% (give or take a few % for old components), I'd say board is good unless I'm missing something.
 
d all my measure points is approx 20% (
probablt DBT is causing that.
IMHO is good to rebuilt power supply, specially if is your unit. In that unit is a simple task just few caps and resistors. Just be careful with pads and traces.
D01 and D02 are proably ok. Does the unit comes out protection without F-2624?
 
probablt DBT is causing that.
IMHO is good to rebuilt power supply, specially if is your unit. In that unit is a simple task just few caps and resistors. Just be careful with pads and traces.
D01 and D02 are proably ok. Does the unit comes out protection without F-2624?


Yes it comes out of protection now, I found the main issue when I measured R26 (3.3k ohm) and it was only 700 ohms in circuit. Pulled it out, tested fine at 3.3k ohms. Long story short, TR10 was toast and basically became a resistor. Replaced TR10 with KSC2383, powered on and green light!

Checking bias and currently (no pun intended), I can only get about 7 mv max across F04...

F05 is running perfect at 30 mv and both channels zero out at DC offset.

I'm going over my work one more time, would like to have this thing back to solid square one before changing caps, etc.

Anyone dealt with one channel not coming up ?

Trim pot tests good at 1k ohms, all voltage test points on 2624 are good as well.

Should I replace caps on the one side first and see if theres any change?
 
see what voltage you are getting at pins 21 and 24 . if these are high take a look at the emitter resistors that appear on a different board according to these schematics . 0.33 ohms 5 watts

expect around +- 600mv on 21 and 24 .
 
see what voltage you are getting at pins 21 and 24 . if these are high take a look at the emitter resistors that appear on a different board according to these schematics . 0.33 ohms 5 watts

expect around +- 600mv on 21 and 24 .

All emitters test ok.

I do have old output transistors installed on this side of the amp in case something gives up, they all test good

Pin 21 -490mv
Pin 24 530mv

Pin 12 -512mv
Pin 9 627mv
 
looks like they need a bit more voltage there . its very late here .. that info is good to know though . it narrows it down a little .
 
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