Sansui 9090db green protector light, no output

Linehand

Active Member
I recently purchased this original condition one owner stereo and after de-oxing switches and pots, its been sounding great last few days. Last night I added a monster power supply with voltage display which is fed from a variac (I have a Fisher 800c mostly original which I run at 110v ac). Well when I turned the Sansui on, one channel sounded a little weak, noticed the voltage at 110v and slowly brought the variac up to 120v at which point the Sansui went into protection mode (flashing red light). It quickly came back out of protection (green light) but there was no sound/output, no FM or AM radio and no tuning or signal strength meter movement at all. I powered down and then back on, it worked briefly then gave a little pop and back to red light protection mode, came back out (green light) but no more sweet music. I bypassed the preamp with another signal to main in but still have no output. All buss fuses are good on the power supply and relay protection boards, I haven't checked transistors or any of the fusible resistors.

So currently the unit powers on and lights up, the relay clicks and the contacts there look fine, the green protector light is on, but there doesn't seem to be any signal past that point.

I'm hoping that these symptoms as described might point to a specific culprit?

Eventually I will have a full rebuild done but I'm not ready at this time...

thanks!

Paul
 
In my opinion, care needs to be taken powering up a solid state amp with a variac. Unlike a dim bulb tester, which limits the current due to the light bulb in series, a variac doesn't have any current limiting component. So what can happen is that the unit can easily draw more current than normal at certain times. I have used variacs for testing after replacing components in the output stage, and many times you will see a heavy draw of current unitl you reach a point where the power supplies are up, and caps are charged, usually after you reach 50 or 60 volts. Then the current comes down as you go to 115v. I am not sure if this initial over current is transformer and power supply based, or output based.
But a unit that hasn't had any work will need those fusable resistors replaced at the least.
But with a green light, the protect says its working. The relays in these units can get very spotty, so you may want to tap it as you have the unit on to see if sound comes back. the green light is actually produced as a signal passes through one of the relay contacts, so the relay is energizing.
 
No question, whatever gave up did so as variac voltage increased from 112 to 120, lesson learned. I've read thru several other threads, all similar but slightly different symptoms. I'm investigating the 1 ohm resistors on the power supply board and transistors on protection board (Tr01, Tr02). I have power to the output transistors. Im sorting thru the schematics...
 
power supply is a good start . cant see why upping the voltage a little caused this . power supply here varies wildly and only seems to destroy washing machines for clothes .
 
I feel the same way, the issue definitely occurred as voltage was being increased. Voltage at this outlet regularly varies from 115-129 without the variac. I remember reading somewhere over voltage was bad for the capacitors and under voltage hard on transistors...

I'm hoping someone who knows the circuit can chime in so Im not chasing rabbits that may or may not be relevant...
 
get the power supply squared away first .after all nothing works if that aint right .

I have the service manual and schematic open but I'm not seeing values for power supply, I may have tunnel vision. When you say square away the power supply are you referring to the voltage values at the transformer?
 
Coincidence, as it was being used for a couple of days the fault was building and the next time you powered it up it just took it into full failure of whatever has failed.
Knowing this amp, PSU first then look at fusible resistors...
 
Thank you guys for the suggestions- i was knee deep into testing power supply, when baby decided it was time to come out so off to the hospital with mama. I found a bad transistor and adjacent resistor on 2624 (tr17 im goin off memory) along with a lot of out of value resistors. I’m here at the hospital with a little downtime trying to line out a repair strategy for this bad boy. I definitly want to preserve the db functionality- i may attack it myself unless i can find a recommended tech here in SoCal. I’m combing through all the old 8080 and 9090 threads in the meantime.... as a side note baby and mama are happy and healthy!
 
Congratulations sir!

This db are usually no that hard, they are just tedious to work specially the DB board.
I would rebuild the power supply first, then the driver and protection, and then the db boards... if you decide to do it your self we're here to assist you.
 
Congratulations sir!

This db are usually no that hard, they are just tedious to work specially the DB board.
I would rebuild the power supply first, then the driver and protection, and then the db boards... if you decide to do it your self we're here to assist you.

Thank you- the collective knowledge here is invaluable and greatly appreciated
 
Power supply voltages are way out. Purple legs feeding main caps @ 41 v. Everything else is indicating negative voltages ranging from 0 to 43.6. R30 and R31 are 55 milliohms (with both legs still soldered to the board, should I remove and check?) I figure a complete power supply rebuild will be necessary.

Also, there are a few components on just one half of 2624. R50 measures open, R44 1k ohm, R66 1k ohm (though it is clearly toasted) and TR18 which burned up as well. The other half of the board has wandered, but are at least in ballpark spec. Either way this board will be done too.

I don't see R66 listed in the service manual, I have found a matching replacement on amazon. Should all diodes be done as well while refurbing the board? I noticed QRXrestore has kits listed, the only thing I don't see are the diodes and TR17/18 (2SA733). I'm assuming these parts are generally not replaced. I've found several replacements which are indicated as compatible with TR17/18, does anyone know which replacement is exact?
 
looks like a rebuild to me .. diodes are cheap whilst in there ..
wondering if supply just died or something killed it .
 
I measured from test point to phono ground if that could be an issue...

Also, I took measurements on top at the purple, yellow, white, green, brown legs into the board. They measure as follows:

P 40.51v
P 40.42v
Y 40.9v
Y 40.9v
W 6.2v
G 6.33v
G 21.3v
B 5.6v
 
always use chassis ground .if the phono grounds go to chassis it should be just fine .. sorry dont have time to look at schematic .
 
Pete Hall probably went to sleep.
Those voltages you measure are AC volts, and not that far off. Make sure the voltage select is set at the proper voltage if this is a worldwide unit. Transformers are usually robust and don't fail easily.
Those 2 resistors R30 and R31 are fusable 1 ohm resistors and may have failed due to problems with the outputs and driver board. Check transistors TR1 and TR2 as they may have opened as well.
You need to remove the output transistors on the same side as the damaged side of the driver board (I believe its the right channel right side) . Check them out of circuit as some may have shorted or opened. When removing the outputs mark their position, and if they are OK put them back in the same position with fresh heat sink compound after cleaning off the old stuff. Check the emitter resistors (0.33 ohm) on the power supply board to see if any have opened. If you find a shorted output, many times you will find an open emitter resistor.
Of course, replace all of the fusable resistors and burnt resistors on the driver board with new carbon film, or preferable by me metal film type. If as you say you have bad transistors and burnt resistors on the driver board, all transistors need to be tested fully for shorts/opens/or leaky. Be very careful on transistor lead placement especially when using replacements as some are ECB, or BCE, or CBE. Same thing with checking and replacing diodes.
I would also check the fuses and make sure that you have the proper values in place.
for initial checkout I would suggest using a dim bulb tester with the driver board removed, and verify that all DC supplies are OK.
Then you can reinstall the driver board and using the dim bulb tester check it out.

But Pete may have more or other suggestions when he rises
 
Pete Hall probably went to sleep.
Those voltages you measure are AC volts, and not that far off. Make sure the voltage select is set at the proper voltage if this is a worldwide unit. Transformers are usually robust and don't fail easily.
Those 2 resistors R30 and R31 are fusable 1 ohm resistors and may have failed due to problems with the outputs and driver board. Check transistors TR1 and TR2 as they may have opened as well.
You need to remove the output transistors on the same side as the damaged side of the driver board (I believe its the right channel right side) . Check them out of circuit as some may have shorted or opened. When removing the outputs mark their position, and if they are OK put them back in the same position with fresh heat sink compound after cleaning off the old stuff. Check the emitter resistors (0.33 ohm) on the power supply board to see if any have opened. If you find a shorted output, many times you will find an open emitter resistor.
Of course, replace all of the fusable resistors and burnt resistors on the driver board with new carbon film, or preferable by me metal film type. If as you say you have bad transistors and burnt resistors on the driver board, all transistors need to be tested fully for shorts/opens/or leaky. Be very careful on transistor lead placement especially when using replacements as some are ECB, or BCE, or CBE. Same thing with checking and replacing diodes.
I would also check the fuses and make sure that you have the proper values in place.
for initial checkout I would suggest using a dim bulb tester with the driver board removed, and verify that all DC supplies are OK.
Then you can reinstall the driver board and using the dim bulb tester check it out.

But Pete may have more or other suggestions when he rises


Thanks Tom- I'm compiling a mouser list, I'll check what you suggest and report back
 
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