SA-9900 Rebuild

[Rsclj]

received this beast for $0.00 was told it doesn't power up...well the initial inspection shows some issues...nothing in the way of blown fuses, (would have been a nice find as a cause for not powering up) but the main filter caps are shot and have leaked...the PS (AWR070) has been hacked upon...some transistors have been replaced and the traces have been royally screwed (on leg of several transistors can be moved thru the board and the trace moves with them) parts for this board were ordered and have arrived so I guess its time to dig in for a total board rebuild. repairing those screwed traces could be interesting, I may have to desolder the wire pins to gain proper access to the foil side of this beast...I will try to unbundle some of the wires to see if I can get a bit more slack...pulling the bad main filters will also give me some more room. thankfully I still have a couple of 100W incandescent bulbs left for the DBT. Thanks to LesE for his extensive component list for this unit, and his PM support already in this process...more to come

 

[LesE]

Once you remove the right side panel and side stay, you will be able to lift the board out of the standoffs and rotate it 90 degrees which should give you pretty good access to the foil side. You can attach a length of wire to one of the holes for the standoffs and tie it off to help hold the board in place while working on it.

 

[Rsclj]

I'll look at that! I had left the side panels both on and removed the little cartridge selector board and the PS board is off its standoffs... Normally I could replace the components as it sits now...but with those bad traces I really want some viewing/working room.

 

[Rsclj]

 

[Rsclj]

the two transistors Q5 and Q6 are the replacements with the bad trace/pads...Q3 looks to be non stock as well...on the other side Q10 is green and looks to be non stock. Looks like the Q5 area has seen some heat

 

[Rsclj]

This has seen some heat...so far fully half of the transistors test as bad ...most testing as open on one side

 

[LesE]

Looks like you're off to a good start. Given that many of the transistors are testing bad, it may be a good idea to give the resistors a quick check while the other parts are removed from the PCB.

 

[Rsclj]

Lifted tabs on this whole section

 

[Rsclj]

PS done

 

[Rsclj]

New parts on good trace

 

[LesE]

Looks good. You're well on your way to having a working amp.

 

[Rsclj]

I would like to DBT it now but out of time for the day

 

[Rsclj]

DBT shows so far so good... more digging can now be done

 

[LesE]

All PS voltages good?

 

[Rsclj]

i'll dig into the voltage testing tomorrow I'm slammed, yesterday I literally had enough time to plug it in to the DBT and turn it on, to witness the brief glow as the caps charged then the bulb go out with power applied...so perhaps a total of 30 seconds to work on it

 

[Rsclj]

Voltages test as good...well after I swapped the leads on Q6...damn my failing eyes...guess it's time for new glasses...but a quick switch of the leads and it comes out of protection on the DBT...on to the next board