SE/30 sound issues: Installed 3rd party ROM in SE/30; sound gone, only static

[techknight]

MMBT3904 = 1A

MMBT3906 = 2A

You could also use MMBTA06 and MMBTA56. 

You can only meter these transistor accurately with diode check on a DMM. Without it, your pretty much shooting in the dark. 

Also, if the transistors have failed, change the op-amp with it.

 

[roj_matt]

MMBT3904 = 1A

MMBT3906 = 2A

You could also use MMBTA06 and MMBTA56. 

You can only meter these transistor accurately with diode check on a DMM. Without it, your pretty much shooting in the dark. 

Also, if the transistors have failed, change the op-amp with it.

So I ordered a few MMBT3904 transistors.  I removed the old one and soldered the new one on.  I now get readings with the resistance check, but still just static (no sound).  I didn't see your updates to this post until after I had already removed the old transistor.  You mention testing it with a diode check is the only accurate way to do it, so now I'm doubting I was even testing it correctly to begin with...  Most online tutorials have you test a transistor using resistance (the negative lead on the emitter or collector, positive on the base should give you numbers in the MOhms).  I have a diode test mode on my DMM, but I'm not sure what I'm looking for.  The numbers I get are in volts instead of ohms...  As you can see, I'm confused.

Do you know the part number for the op-amp?  The writing on it says "TL071B 804".  There appear to be a few different TL071B chips out there.

Anyway, now that my original diagnosis is in question, is replacing the op-amp still the next best thing to try?

I'm not quite ready to give up yet, but just out of curiosity, what is the typical going rate for you or others to troubleshoot and fix boards?

 

[techknight]

Any time the output transistors fail, the TL071 has to be replaced with it. 

as for testing transistors, most of the sites do tell you to check it in ohms. Those sites suck and likely dont have much electronics experience whatsoever. 

The best way to do this is using diode check on your DMM. on an NPN, youll get .4XX to .6XX between base to emitter, and base to collector. positive on base. Reverse the leads, you get nothing. Also C to E you get nothing. 

PNP is the opposite. Black lead on Base, otherwise you get nothing. 

 

[roj_matt]

Any time the output transistors fail, the TL071 has to be replaced with it. 

as for testing transistors, most of the sites do tell you to check it in ohms. Those sites suck and likely dont have much electronics experience whatsoever. 

The best way to do this is using diode check on your DMM. on an NPN, youll get .4XX to .6XX between base to emitter, and base to collector. positive on base. Reverse the leads, you get nothing. Also C to E you get nothing. 

PNP is the opposite. Black lead on Base, otherwise you get nothing. 

I guess you're "techknight" for a reason.  I replaced the op-amp and once again the sound is working loud and clear!  Thank you!  I have searched these forums over and over looking for people whose SE/30s had similar symptoms to mine, and haven't found any that quite matched.  Hopefully this thread helps someone else.  So to summarize what I did to fix this issue:

- after a successful recap, the sound mysteriously faded to static (completely unrelated to the new ROM chip I happened to install at the same time)

- performed continuity tests between capacitors (c1 - c10) and the Sony sound chips (everything checked out)

- used a DMM (digital multimeter) on diode test mode to test the Q1 NPN and Q2 PNP transistors; Q1 was in doubt

- I replaced Q1 (didn't fix the problem)

- I then replaced the op-amp chip (UA9 on the board)

That did the trick!  No more static!  The power-on chime is loud and clear!

 

[techknight]

Well, thats a nickname a buddy of mine gave me back in high school. 

I am just a very experienced repair tech, I know what to look for... 

 

[james_w]

This could be super useful in future, thanks chaps

 

[olePigeon]

Someone should add it to the Wiki.