Sansui 771 Clean-up

[mrk229]

I was able to get back to this yesterday. I reflowed the TR06 pins, but did not get any change to the previous results and went ahead and desoldered and removed TR06 which is a 2SD330 NPN. With that removed I checked it with my DMM in diode mode based on a test method I found on-line:

+to base, - to collector = .6 - .7 Vdc, actual .595 vdc
+ to base, - to emitter = .6 - .7 Vdc, actual .694

- to base, + to collector = 0Vdc, actual "OL"
- to base, + to emitter = 0Vdc, actual "OL"

So if I'm doing this right and as mrk229 expected the TR06 2SD330 is bad. From checking other posts it sound like the TP41 is a good replacement that may be useful for other applications.

Actually that looks like the transistor is OK. You should test it one more way.

Check collector to emitter swapping the + and - leads as you did before.
That makes it a six way test. it should be 0 or "OL" both ways.

 

[Nikkotopia]

Thank you, appreciate the coaching! I will check that today and reply.

 

[Nikkotopia]

I ran the 3rd test and
- to collector, + to emitter = "OL"
+ to collector, - to emitter = "OL"

Then I rechecked the first tests
+ to base, - to collector = .595 or very close, always about the same
+ to base, - to emitter starts out at 1.2 or so, then settles in a few seconds to .62 to .64. I did this a few times and for several tries I was just getting "OL"

Could it be that with in circuit conditions this NPN will be failed open at the emitter?
.

 

[mrk229]

I ran the 3rd test and
- to collector, + to emitter = "OL"
+ to collector, - to emitter = "OL"

Then I rechecked the first tests
+ to base, - to collector = .595 or very close, always about the same
+ to base, - to emitter starts out at 1.2 or so, then settles in a few seconds to .62 to .64. I did this a few times and for several tries I was just getting "OL"

Could it be that with in circuit conditions this NPN will be failed open at the emitter?
.

That B to E reading is not good, the voltage drop should be stable just like the B to C reading. Unless your meter is not making a really good connection to the emitter lead, those B to E readings say to me replace it.

 

[Nikkotopia]

Thanks, that sounds like the culprit. I'll get the TP41 on order and let you know how it all turns out

 

[billyz]

On my 771 the FM was out. It was one of the Transistors TR05 or TR06 I believe. Very common issue with these.

 

[Nikkotopia]

Been busy decking the halls, but got some TP41's Mouser for the TR06. The first one a pulled out of the package spec'd out OK so I installed it. I did not get 13.6 Vdc at the TP 26, but my soldering may be suspect. I'll check it out some more this weekend. More deking the halls to do.

 

[Nikkotopia]

Finally getting back to work on this. I replaced TR06 with the TP41, but did not get 13.6 V at TP26. I didn't like the looks of my soldering for TR06 so I removed it, checked the B, C, E per the previous test, all good, so I reinstalled. Still not getting 13.6 V. B = 46 V as before, but C = 51mV and E = 40 mV. Also, ZD01 which was 13.6 V before I did anything is now 1V on the collector side and 21 mV on the ground side. Hope I didn't make things worse. On the good side I am getting 32.95 V at TP 25, so that adjacent part of the pwr brd is apparently OK. I'm checking other nearby voltages and will post results later today or tomorrow.

 

[Nikkotopia]

Here are some voltages I was able to take from the circuit around TR06. I see that R04 on the schematic does not exist on the PCB, but on the trace side is a jumper over to I think the base of TR05.