Sansui 9090 (DRV-BRD/F-2436) Resistor R42 smokes??

With a lot of luck and the right combo of parts changed, I have been able to get it to power up with out smoking anything. I did notice that the fix to keep it from smoking resistors was by changing TR07 and TR08. I was lucky in finding a suitable substitute for those transistors.
I began doing bias checks and found that the Left channel is not adjusting. From the speaker outputs the Left channel is reading 15.5 VDC.
When checking at F07 for current it reads about 150 mA and will not adjust.
Also, the Left power meter spikes to about 200 watts and stays there steady.
I'll keep trying with my fingers crossed and let you know if there is any progress.
 
That is too much voltage on the output, you are looking for zero volts and 50 ma of current for the 9090. The differential pair of TR01,TR03,D01,D03,VR01 are in the suspect area for the 15 volts across the output. The high bias current may normal after fixing the offset voltage.

The fuse ratings are stamped below the fuses but here they are, I have a 9090 open now and for the next few days. Page 10 of service manual shows fuse location and values.

F01 - 1 AMP 250V
F02 - 1 AMP 250V
F03 - 10 AMP 250V
F04 - 10 AMP 250V
F05 - 3 AMP 250V

The following fuses are next to the driver board 7 and 8 are the inner fuses 9 and 10 are the outer ones.

F07 – F10 6 AMP 125V Marked on my circuit board
F07 – F10 7 amp 125V on the pictorial of the my service manual.
 
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If there is 15v on the speaker outputs, it should not come out of protect... You better take a close look at that relay. It might be welded shut.
 
If there is 15v on the speaker outputs, it should not come out of protect... You better take a close look at that relay. It might be welded shut.

NOPE! not the relay.
It comes out of protect fine. I disassembled the relay and it still looks brand new. No issue there.

I wanted to see if would crossover to the RIGHT side outputs so I flipped the Driver Board and tried it the opposite way. Sure enough! the 15 to 18 volts followed.

So I am back to looking at the driver board. I retested the output transistors and there were no issues there either.
 
Good news and Bad news!

I de-soldered and replaced every Capacitor, Resistor, Diode, and Transistor on the Driver Board. Also, replaced all main output transistors.
I was able to power up and set the bias and output voltages. All were within ranges expected in the manual. Near 0 vdc for the outputs and under 50mA for the bias.
Attached the speakers and it came out of protection mode but the only sound out of the speakers is a low hum and the needles are not moving. The sound was not adjustable by the volume control.

hmmmm?

Looking for help or ideas for the next step.
 
I de-soldered and replaced every Capacitor, Resistor, Diode, and Transistor on the Driver Board. Also, replaced all main output transistors.
I was able to power up and set the bias and output voltages. All were within ranges expected in the manual. Near 0 vdc for the outputs and under 50mA for the bias.
Attached the speakers and it came out of protection mode but the only sound out of the speakers is a low hum and the needles are not moving. The sound was not adjustable by the volume control.

hmmmm?

Looking for help or ideas for the next step.

ANY help out there??
 
I am having the same exact problem. Pull my driver board and green light comes on,put in and it goes into protection mode. I have checked and replaced all bad transistors and checked all resistors and diodes and compared left to right side and they are exact. I was wondering if it could be the protection board causing it. When I pull the driver F2436 and I put my red meter probe on the relay on the protection board that causes it to go into protection mode to. I take it off and it comes back. I seen someone on here said a resistor on the protection board may cause this. I think out of the driver board with no audio driving it the output from both channels to the protection board is suppose to be 0 volts and anything above 2.5 and -2.5 volts is suppose to put it in protection. I am an avionics tech for Fedex and this one has me stumped with out another driver board to see if it will work. like I said I have checked everything on that board and any advise would be greatly appreciated. How do I adjust the bias pots and the other ones.

Topper maybe we can work this out since we have about the same problem. I found my schematic of my 990 (not db or 9090)I bought mine in germany in 1976. I found the errors on the print like they had pin 38 of the power supply board listed twice. I found it was actually pin 34. I now have all my 6 transistors in the back off and was wondering if anyone knew if you can plug in the driver board without those transistors in and not cause any damage. I figured if I keep the speaker switch off it would not send the signal their. Last time before I blew R 29 and R30 I had -61 volts going out to the protection board which i know will keep it protected. That would mean something is wrong with my driver board to which everything reads correct now. Could it be those adjustments which I never touched ever need adjust because of the new transistors I put in? I was able to download the 8080db/9090db/890db/990db schematic free on line but even those are different from my 990. I was told they where almost exact but it only shows 4 rear transistors in the back on this print. The picture of your driver board you posted is just like mine only mine has 2 regular fuses in place of the real low resistors.
 
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I am having the same exact problem. Pull my driver board and green light comes on,put in and it goes into protection mode. I have checked and replaced all bad transistors and checked all resistors and diodes and compared left to right side and they are exact. I was wondering if it could be the protection board causing it. When I pull the driver F2436 and I put my red meter probe on the relay on the protection board that causes it to go into protection mode to. I take it off and it comes back. I seen someone on here said a resistor on the protection board may cause this. I think out of the driver board with no audio driving it the output from both channels to the protection board is suppose to be 0 volts and anything above 2.5 and -2.5 volts is suppose to put it in protection. I am an avionics tech for Fedex and this one has me stumped with out another driver board to see if it will work. like I said I have checked everything on that board and any advise would be greatly appreciated. How do I adjust the bias pots and the other ones.

Welcome to the Exclusively Sansui Forum tducksoup1.

Your problem does not appear to be exactly the same as the problem described by the thread starter (i.e. the 'OP') in this thread. And thus you should start a new thread for your problem - not tag your issue on to the end of other threads which may be months old and thus 'cold'.

For the bias and DC offset pots adjustment procedure you will need the service manual - which is available online, and possibly available here on AK.

give me a minute i'll post the link to it if it is here on AK...

Here is the link to the 8080/9090 Service Manual.
http://akdatabase.com/AKview/displayimage.php?album=28&pos=47 - open the link, then right click on the large PDF icon and select Save Target As...

Good luck.
 
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