kevzep
Its all about the Music
Incorrect, you do not want the circuit to handle more current, the resistor is there for sacrificial purposes and to protect the amp from major damage, and to localise the failure.
So replace 1/4 watt with 1/4 watt.
Sansui 9090: Original, everything works. Should I change anything?
- Thread starter KeithD
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So replace 1/4 watt with 1/4 watt.
danrclem
Super Member
OK, so we've covered diodes, e-caps, variable resistors, and fuse resistors. Are there any transistors in here to think about replacing? I only see a few 2SC1313 transistors, which are on the bad transistor list.
By, the way, just to be clear Kev, I have a 9090 not 9090DB. I don't think that changes any of your advice, just want to be clear.
By, the way, just to be clear Kev, I have a 9090 not 9090DB. I don't think that changes any of your advice, just want to be clear.
Here's the system as I have it set up now. Sansui 9090 with Pioneer PD-M703 CD player, Technics cassette deck, and AR 4x and AR 6 speakers. Sounds nice and like the visuals. 
I do plan to change the troublesome diodes, fuse resistors and caps on the driver and power supply boards. I've only got the diodes in stock, so will need to order the rest. But for now, it really has a great sound. Thanks again for everyone's help and education about this great receiver!
I do plan to change the troublesome diodes, fuse resistors and caps on the driver and power supply boards. I've only got the diodes in stock, so will need to order the rest. But for now, it really has a great sound. Thanks again for everyone's help and education about this great receiver!
kevzep
Its all about the Music
Doesn't matter, it applies to anything this old, but its up to you at the end of the day, personally I would be giving it the complete work-over so as to get the best and most reliable performance from it.
Trnsfmr_Jr
New Member
I use a 1/2 watt resistors and lower the fuses from 10A to 6A or 7A for a little added protection. In my opinion these fusibles never did a great job of protecting these boards, they often just go out of spec instead of acting as a fusible. This can cause a whole host of other problems. If you're going to get in there I would suggest replacing TR01 through 04. The differential pair for each channel- They often start failing and send DC spikes through the amp. Edit: forgot to mention- you can use KSC1845 to replace those TRs you're talking about
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Would you use a 4Amp fuse to replace a 2A fuse?
Trnsfmr_Jr
New Member
Haha, of course not. I have just fixed over 200 F2624 boards, and over 150 F2436 boards. I've never seen one of these fusibles "save" a section of this amp. I believe that many of them are handling very close to a 1/4 watt already and that is why they go out of spec rather than actually "fusing". When that happens they cause many other other problems. I've seen transistors on these boards literally exploded when one of these fusibles is directly on the collector or emitter. The fusible did nothing. I don't really regard them as protection, but more as another point of failure.
Thanks for that info on the transistors. I do have lots of KSC1845F on hand.
Just placed an order with Mouser. Ordered 1/4 W metal oxide resistors for the fusibles. However, 4.7 ohm, 1/4 W were out of stock, so went with 1/2 W for those four. Based on your suggestion I will change the fuses on the PS to the lower value, so I should be ok. For now, just ordered caps for the driver and PS boards. I'll worry about the rest of the caps later, as I have limited time to work on electronics these days. Once parts arrive, I'll be back to double check locations on the driver board. Since I have the factory modified board, I noticed it is different from the service manual, and at least two of the fuse resistors are in different locations.
Trnsfmr_Jr
New Member
Yea. Those 22ohms down at the bottom left and right of the board- they change their production on those driver boards depending on whether they have those stand-off barrel fuses on the drivers. You may have one of the 9090s where they have already lowered the values of the fuses for the rail voltages. Later models start using the 6A or 7A as I suggested. There are about 3 different versions of that same board. Just follow what is there already and you'll be fine.
Thanks, yes, I see R43 and 44 have been moved. The others look to be in place as indicated on the board and in the service manual.
I checked my PS board, and I do have 10A fuses in place for F08-10. Service manual copy I have calls for 125V/7A. Will pick up either 6 or 7A fuses tomorrow depending on what is available at the local hardware store. Also, tnsilver's recap list has C11-14 as 4.7µF/80V non-polar caps on the PS, and this is what I ordered at Mouser: https://www.mouser.com/ProductDetai...5Yq7AV/vNog==&countrycode=US¤cycode=USD However, the service manual shows these caps as having polarity on the PCB diagram. Did I order the right caps?
I checked my PS board, and I do have 10A fuses in place for F08-10. Service manual copy I have calls for 125V/7A. Will pick up either 6 or 7A fuses tomorrow depending on what is available at the local hardware store. Also, tnsilver's recap list has C11-14 as 4.7µF/80V non-polar caps on the PS, and this is what I ordered at Mouser: https://www.mouser.com/ProductDetai...5Yq7AV/vNog==&countrycode=US¤cycode=USD However, the service manual shows these caps as having polarity on the PCB diagram. Did I order the right caps?
kevzep
Its all about the Music
just replace them with whatever is in there, its not good practice to rely on the service manual for that sort of thing, they are often wrong as there are many updates along the production of these amps and they are not often if ever recorded in the service manual, or service bulletins.
Here is the update. I worked on the driver board today (F-2436-1).
Replaced D05,06 with 1N4148, tested with DBT - OK, line voltage - OK.
Replaced all e-caps: C01,02,07,11,12. Tested with DBT - OK, line voltage - OK.
Replaced fuse resistors: R47-50 with KOA Speer metal oxide (MOSX1/2CT52R4R7) 4.7 ohm/1/2 watt (1/4 watt was out of stock).
For R29,30,43,44,45,46 for some reason I ordered KOA Speer metal film resistors. I guess I was not paying close attention. These are all 1/4 watt.
R39,40 are listed as fuse resistors in the service manual, but are not on trnsilver's list of replacements, so (not double checking) I did not order replacements for these.
Tested on DBT - was slow to come out of protection, but did. Tried line voltage - would not come out of protection.
Pulled the driver board and it comes out of protection on line voltage, so problem is clearly on the driver board.
I did test every component I pulled (except the diodes) and all were within spec except one of the 390 ohm fuse resistors.
SO, now what? I can try putting the resistors back in one by one and test after each one, to see if one of them is the issue. I've double checked all of my solder joints. Will double check that all of the new resistors are correct.
Replaced D05,06 with 1N4148, tested with DBT - OK, line voltage - OK.
Replaced all e-caps: C01,02,07,11,12. Tested with DBT - OK, line voltage - OK.
Replaced fuse resistors: R47-50 with KOA Speer metal oxide (MOSX1/2CT52R4R7) 4.7 ohm/1/2 watt (1/4 watt was out of stock).
For R29,30,43,44,45,46 for some reason I ordered KOA Speer metal film resistors. I guess I was not paying close attention. These are all 1/4 watt.
R39,40 are listed as fuse resistors in the service manual, but are not on trnsilver's list of replacements, so (not double checking) I did not order replacements for these.
Tested on DBT - was slow to come out of protection, but did. Tried line voltage - would not come out of protection.
Pulled the driver board and it comes out of protection on line voltage, so problem is clearly on the driver board.
I did test every component I pulled (except the diodes) and all were within spec except one of the 390 ohm fuse resistors.
SO, now what? I can try putting the resistors back in one by one and test after each one, to see if one of them is the issue. I've double checked all of my solder joints. Will double check that all of the new resistors are correct.
kevzep
Its all about the Music
Its called preventative maintenance, most of the components are at the end of their service life, changing them prevents a more catastrophic event happening and damaging irreplaceable parts.
Update: turned on the receiver today on line voltage and it came out of protection, but there was static in the R channel, which once in a while put it into protection. I recalled that I had straightened TR09 and 10. I think TR09 was particularly bent over. Figured it might be a cracked solder joint from moving that transistor back and straightening or a bad transistor. I swapped TR09 and 10. Solved the problem of dropping into protection, though still hearing some intermittent faint crackling. What is the replacement for TR09,10? I found this in another thread: TR09, TR10 2SC1720 --> KSC3503DSTU. I do have that on hand. Is this the recommended replacement?
kevzep
Its all about the Music
This sort of random thing is going to keep happening until you do the full restoration. Just go through the whole thing, do it once do it right. Otherwise you'll have to keep opening it up all the time.
Hipocrates
Super Member
there:
http://audiokarma.org/forums/index.php?threads/9090-driver-amp-transistors-pinout-caveats.811607/
Listen to kevzep.
IME, with sansui, they will misbehave sooner or late until properly reconditioned.
Static issue is gone. Playing beautifully now. I was able to sand and refinish the case. It's getting a good dry in the fume hood at work. Too cold to do that in the garage now. I've got the parts to do the e-caps on the power supply, but based on the fact that none of the e-caps on the driver board were out of spec, I don't feel it is necessary to replace those caps at this time. I can do that when I have some spare time to work on this fine receiver again. I do feel better now that I've replaced the two troublesome diodes and the fuse resistors. Still have two to go that were not on the list I used.
Thanks for the link for the transistor replacements!
Thanks for everyone's words of advice and caution. It's been a great learning experience, and this receiver lives up to its reputation.
Thanks for the link for the transistor replacements!
Thanks for everyone's words of advice and caution. It's been a great learning experience, and this receiver lives up to its reputation.
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