Sansui 9090, power ON, no sound in both channels

divu

divu

Active Member
Hello everyone..
I have in my collection a beautifull Sansui 9090.I read a lot's of posts about recap.Yesterday I changed in F2436-1, all the electrolytic capacitors, tr09, tr10, and all four V- pots with multiturn...He started the amplifier with the DimBulb, I made the first setting of bias, and everything okk.. After an hour I se that the ampli heats too much, so I made another bias setting .. all ok with the left channel .. I power off the ampli, unplug the cord of the wall, and at remove the 10A fuse right channel, I have inadvertently made a bridge between This and the heatsink of the neighbor transistor Tr02 in F 2546 board... It has made a small spark ... When the ampli starts again, the relay acting, the led light changes to green, but I do not have any sound in any of the channel..Stereo Light on FM not working(before this the stereo light working)... Please help me to repair this nice ampli Sansui 9090 .. I have a multimeter, iron soldering, but my electronic level skill it's poor...Sorry for my bad english..(I'm living in the Spain)...Thanks in advance....
 
Check none of the fuses on the PS board (F 2546) were blown as a result of the short. Use a meter. Some are hard to spot visually.
 
Many thanks..I have checked all fuses, yesterday, with the multimeter.All its okk..I think the voltage current passing in collector pin of the Tr02...I'm çhecking also the Tr02(out of board based in EchoWars thread) and seems be good...I don't know which it's the next step....Regards
 
It's been a long time since I futzed around with a none DB 9090, but out of the top of my head here are a few pointers:
  • Look up a DBT (Dim Bulb Tester) and build one if you haven't already. Do all repairs with the unit on a DBT otherwise you might escalate the problem.
  • The main filter caps don't bleed on shut down. You must discharge them (like with a 100W light bulb) before handling the unit - or they might bite hard!
  • Never pull or insert fuses / boards while the unit is fed or the filter caps are charged
  • The pre-amp and amp can be tested stand alone by pulling out the jumpers at the back and separating the sections. You could for example, hook up another external pre-amp to the 9090 main-in and test just the 9090 amp. Or you could route the 9090 pre-out to another external amplifier and test the 9090 pre-amp section. If the pre-amp works, you know the fault is on the driver amp.
  • The 9090 has rather fragile PCB rails. They lift, break and burn easily. Make sure the short had not opened traces on the driver amp (F2436) and power supply boards.
  • The 9090 driver amp board F2436 has a couple of glass fuses on it, perhaps check them too, before going further.
  • Going further means checking all of the fusistors/resistors and semi-conductors on the driver amp verifying resistance values and E/C/B junctions.
  • The relay engages and the green LED is lit when the driver amp is functioning properly and DC levels that reach the speakers are bellow a certain threshold (measure DC voltage at speaker terminals - what do you get for each channel?). The same applies when you take out a faulty driver amp. If you got the driver amp installed. the pre-amp section is OK, green LED but no sound... It could be the unit 'thinks' the driver amp is not there at all. This cam happen if there are broken traces, burnt fuses, fried resistors etc... so I'd look close at the driver board and the traces that lead to/from it.
  • Once the fault located and remedied, you must follow the DC offset and bias current adjustment procedures as per the service manual.
  • Stay on DBT until then and remember to discharge the filter caps
 
First with power off I would pull all the fuses, and there are quite a few to test out of circuit with your multimeter as a visual might not find a fault. Once that is finished follow tnsilver's steps and report back and will continue from there.
-Lee
 
TR02 that you accidently shorted to is the Series Pass regulator transistor for the 36Vdc used on the tone amp and possible other boards. Without that, you will get green protector light, but no sound. I would suggest checking pin 15 on the 2546 board and make sure you have the +36v. This voltage passes to and appears on pin 34 to the 2541 board (with the big function selector switch on it) and pin 13 on the 2543 board, as well as pin 5 on the 2544 tone board. If this voltage is missing you have either or or 2 bad fuses (F1 or F2 on the 2546 board), or a bad transistor or transistors in the 36v regulator ckt. on the 2546 board (TR2, TR1, or TR3), or even fried zener diode ZD1 on this 2546 board.
Good luck
Just noticed that this same 36v feeds to small power supply regulator on pin 3 of the 2431 board. This is used to develop the 12v DC for the AM and FM circuits which will prevent stereo light as well as any signal strenght either (no radio)
 
Last edited:
I'm checked Tr01 and Tr03.Both transistors it's burn's.I ordered all the replacement pieces(3 transistors, D01, all E.C cap's) in DigiKey...All fuses (measurement out of board) it's ok..Diode ZD01(m. out of board) it's ok..Must waiting 8-10 day's from the replacement part's...When replace the transistor 01 and 02, i will be proceed to +36V at pin nr.15 in F-2546 board..Many thanks at all, specially to Tom B. for detailed explanation..We will keep you informed..Regard's...
 
Hello everyone. Today I'm replacing Tr01, Tr03 with KSC2383YTA, OnSemi, and Tr02 with MJE15032G. I check pin 15 in the 2546 board and here i have +38v(exactly= 37.9V)..This voltage it's good at this point?
 
Looks good.
Pin 15 is +40 and pin 18 is a little higher +45. There's a little fudge factor +-3 volts or so.
If your on the DBT then its spot on.
 
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