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Sansui driver transistor alternative

Seems base of TR809 is not getting the proper voltage. Work your way down now. The resistor in series should cause a voltage drop on the base.

Trying to help but it's quite confusing the transistors aren't numbered on the schematics.
 
Rhod said:
r! I was misinterpreting the spec sheet when orientating the replacement - aaah!
Click to expand...


have definitely done this. Had a set of amps that I couldn't make work for a couple of weeks before taking a break from them. Came back to it and realized I had put the transistor in backwards. Worked perfectly fine once I flipped them.
 
gadget73 said:
have definitely done this. Had a set of amps that I couldn't make work for a couple of weeks before taking a break from them. Came back to it and realized I had put the transistor in backwards. Worked perfectly fine once I flipped them.
Click to expand...

Glad I'm not the only one! Mine seemed to work perfectly once I flipped mine - however, it didn't last!
 
Roger_88_K said:
Seems base of TR809 is not getting the proper voltage. Work your way down now. The resistor in series should cause a voltage drop on the base.

Trying to help but it's quite confusing the transistors aren't numbered on the schematics.
Click to expand...

You're not wrong! I've tried to label the relevant area - attached. Does this help? I've been peering at faded numbers on the circuit board. At least they're labelled there (when not hidden underneath the component itself!)
 

Attachments

Check TR805. It seems it is not conducting.
Although the collector voltage is right, the base and emitter is not. Could mean it is failing.
Also pull R825 and check the resistance. Measure voltages at the diodes, both channels and in both directions, anode and cathode.
 
Rhod said:
Glad I'm not the only one! Mine seemed to work perfectly once I flipped mine - however, it didn't last!
Click to expand...


I may have installed new ones, I don't exactly remember. I bought a bag of 10 because they were cheap.
 
OK, here goes:
R825 reads 330 ohms on the nose.

Diode voltage readings:
D801
Cathode: 2.3
Anode 3.7

D802:
Cathose 23.7
Anode 25.0

...so a bit of a discrepancy there!

TR805
Reads open circuit +ve Emitter to -ve Base

So looks like this transistor might be at fault!
 
Thanks for the update. Just to make sure, you pulled TR805 and tested it with a MM using the diode function?
The resistor is in excellent condition.

Rhod said:
OK, here goes:
R825 reads 330 ohms on the nose.

TR805
Reads open circuit +ve Emitter to -ve Base

So looks like this transistor might be at fault!
Click to expand...

I think you tested the transistor in the wrong direction.
It's an NPN transistor, did you check using the probes from base to collector and base to emitter?
The +VE or RED probe is on the base for both tests. If it still reads open. It's faulty indeed.

However I think the transistor is fine.
TR805 base is not getting the right voltage. The base is connected to the anode of D801 so this should be about 25v. compared to the working channel.

The only way to get a voltage around 25v is from the voltage divider.
Maybe the voltage drop over R813 and R815 isn't correct. Have you checked those two resistors?
 
I think you tested the transistor in the wrong direction.
Click to expand...

Given my transistor track record that is entirely likely . I had it noted as a NPN but will definitely check again, along with those resistors...
 
I think your TR803 is bad, shorted C-E. That pulls the output toward the ground and draws a large base current from TR807. You have approximately 300mV in the emitter resistors on the left channel, that's a lot of current.
 
Well, @Roger_88_K , once again thanks! My record with transistors isn't improving
B-E = 761
B-C = 753

Resistors R813 and R815 test fine according to spec.

@ecluser - TR803 tests fine too
B-E = 770
B-C = 763
 
I usually do a C-E check too just for poop and laughter. It should read open, but once in a while you'll find a C-E short and that means the transistor is junk. Not super common to find good B-E and B-C but bad C-E but not impossible either.
 
gadget73 said:
I usually do a C-E check too just for poop and laughter. It should read open, but once in a while you'll find a C-E short and that means the transistor is junk. Not super common to find good B-E and B-C but bad C-E but not impossible either.
Click to expand...
Good one to keep in mind, Gadget73.
 
Thank you, both: yes, I only reported the B-E and C-E but I actually checked all 6 permutations and all the others read open.
 
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