Sansui G-7500 Fried Resistors F2980 Board

[kevzep]

looks possible TR19 is poorly soldered . can you replicate same scenario ?
or maybe having meter hooked up it defeated over-current sensing somehow ..

TR19 drives the protection, it will hold it on protection but it will not cause the DBT to stay bright.

#2 and #4

Okay, I think during your testing you might have lost an output or driver transistor.

Measure the Output and the Driver transistors.
TR15, 16, 17, 18. are the drivers. They have little heatsinks.

The ones on the heatsinks are the output transistors.

Do you know how to test transistors using the Diode function on you Fluke 117?

Measure B>E/ B>C/and C>E.

You are looking for a short circuit, you can test them in circuit.

 

[Young46]

TR19 drives the protection, it will hold it on protection but it will not cause the DBT to stay bright.



Okay, I think during your testing you might have lost an output or driver transistor.

Measure the Output and the Driver transistors.
TR15, 16, 17, 18. are the drivers. They have little heatsinks.

The ones on the heatsinks are the output transistors.

Do you know how to test transistors using the Diode function on you Fluke 117?

Measure B>E/ B>C/and C>E.

You are looking for a short circuit, you can test them in circuit.

Yes, I know how to test transistors using the Diode function on my meter. So just test them in circuit the same way as not in circuit?

 

[petehall347]

TR19 drives the protection, it will hold it on protection but it will not cause the DBT to stay bright.

i will back out for a while . i assumed it was for current sense for protect . these schematics are hard to figure out .. arrows with numbers and all that ...

 

[kevzep]

Yes, I know how to test transistors using the Diode function on my meter. So just test them in circuit the same way as not in circuit?

Yes, just the same way.

i will back out for a while . i assumed it was for current sense for protect . these schematics are hard to figure out .. arrows with numbers and all that ...

It is the current/DC sense, this part is correct, but they never fail, never in all the F2980 boards I have done, have I seen one fail. I remove these transistors when fault finding on these amps, this will be my next suggestion.

 

[petehall347]

Yes, just the same way.



It is the current/DC sense, this part is correct, but they never fail, never in all the F2980 boards I have done, have I seen one fail. I remove these transistors when fault finding on these amps, this will be my next suggestion.

yes .. i wondered if poor solder was disturbed and defeated it . or meter resistance .

 

[kevzep]

yes .. i wondered if poor solder was disturbed and defeated it . or meter resistance .

Thats why its best just to pull it out, get it out of the equation....

I am thinking there will be some shorted silicon ....probably outputs....we'll see what happens next...

 

[Young46]

Yes.
In this particular case, will be hard to get help... Specifically in Sansuis with F2980 boards.
Same goes for example on Pioneer SA-9900 or Marantz 1250 on the other forums.
That been said, with another units AU's from the 70's, X0X0 or G-X000's, you will get more help, just like the Pioneer forum with SX receivers or Marantz 22XX on the marantz forum.
What I'm trying to explain you (with my limited english) is that, they are some units there that would be very hard to get someone to remotely fix your amp no matter what forum you are, and your unit is one of those.

And that doesn't mean that people do not want to help you, or that some techs feels like food are being taken from their tables, as you distastefully said.

BTW, Self entitlement won't get you more help.

Thought I better reply. I mistakenly took the comments from more than one of the techs to mean something it didn’t. More than one said they could fix it if they had it on their bench. I was wrong. I know now that they did not mean they would not help. You are correct. It was distasteful and I’m sorry I went there. But, I don’t feel that I’m entitled to anything.

 

[kevzep]

Thought I better reply. I mistakenly took the comments from more than one of the techs to mean something it didn’t. More than one said they could fix it if they had it on their bench. I was wrong. I know now that they did not mean they would not help. You are correct. It was distasteful and I’m sorry I went there. But, I don’t feel that I’m entitled to anything.

No need to post this sort of thing, post the results of your transistor testing....

It is easier when its in front of you though...luckily I am working on one at the moment....

 

[Young46]

No need to post this sort of thing, post the results of your transistor testing....

It is easier when its in front of you though...luckily I am working on one at the moment....

I will. Right now I am having to stay close to the throne since I started that prep for my colonoscopy and endoscopy tomorrow morning.

 

[Hyperion]

I started that prep for my colonoscopy and endoscopy tomorrow morning.

Good luck!

 

[Young46]

Good luck!

Thanks

 

[Young46]

TR19 drives the protection, it will hold it on protection but it will not cause the DBT to stay bright.



Okay, I think during your testing you might have lost an output or driver transistor.

Measure the Output and the Driver transistors.
TR15, 16, 17, 18. are the drivers. They have little heatsinks.

The ones on the heatsinks are the output transistors.

Do you know how to test transistors using the Diode function on you Fluke 117?

Measure B>E/ B>C/and C>E.

You are looking for a short circuit, you can test them in circuit.

Attached are my readings for TR15-18

 

[Young46]

Here's more. The output TR's are for the right channel. Trimmer pots adjusted per kevzip instructions.

 

[kevzep]

Okay looks like no Output transistors are shorted out, so lets measure the emitter resistors.

Ω setting, do that and lets report back.

 

[Young46]

Okay looks like no Output transistors are shorted out, so lets measure the emitter resistors.

Ω setting, do that and lets report back.

10 photos attached with readings

 

[kevzep]

Okay good. That looks fine.

Now, measure Ω between the Driver EMITTER, and the corresponding Output transistor BASE. The Schematic I have doesn't make any sense for the output transistor numbers but I will outline what you need to do....

You are trying to measure from the NPN (2SC) driver EMITTER to the NPN (2SC) Output transistor BASE.

Then the PNP (2SA) Driver EMITTER to the PNP (2SA)Output transistor BASE

You should get 4.7Ω, but with the track and meter resistance, it might be about 5Ω.

If you don't understand what I am asking you do, come back and ask more questions.

 

[Young46]

Okay good. That looks fine.

Now, measure Ω between the Driver EMITTER, and the corresponding Output transistor BASE. The Schematic I have doesn't make any sense for the output transistor numbers but I will outline what you need to do....

You are trying to measure from the NPN (2SC) driver EMITTER to the NPN (2SC) Output transistor BASE.

Then the PNP (2SA) Driver EMITTER to the PNP (2SA)Output transistor BASE

You should get 4.7Ω, but with the track and meter resistance, it might be about 5Ω.

If you don't understand what I am asking you do, come back and ask more questions.

I understand but I have a question. The output transistors are mounted on the F-2981 board. The s/m shows them from the conductor side with TR601 on your right and TR602 on your left. The base from TR601 goes to pin 56 and traces to R60 to TR16. The schematic shows the opposite...TR602. I have the transistors installed the way the F-2981 shows them in the s/m and as I described above. This would make them installed wrong according to the schematic. Am I wrong?

 

[Hyperion]

Note that the individual board diagram for F-2891 shows the conductor side, not the component side.

As a check for transistor positioning:-

The collector of the NPN transistor 2SC2581 should go to the +ve rail.
The collector of the PNP transistor 2SA1106 should go to the -ve rail.

The diagrams for the F-2891 boards on the main schematic are labelled incorrectly as they get the TR numbers round the wrong way for one or other of those boards - transposing 'TR601' & 'TR602' against the type numbers - which could have thrown you a curve. (like it would for anyone ).

Best double check the positioning of the transistors - but don't move anything until Kev chimes in with his expertise.

In any case check those resistors for Kev - if they are high resistance they will throttle any attempt to set the bias.

 

[kevzep]

The reason I want to check from one transistor to the other is to check the resistor, but to also check the copper traces on the board, and make sure the transistors are talking to each other, these boards have VERY thin traces and the pads are very fragile.

So check those things out and come back to us.

 

[Young46]

The reason I want to check from one transistor to the other is to check the resistor, but to also check the copper traces on the board, and make sure the transistors are talking to each other, these boards have VERY thin traces and the pads are very fragile.

So check those things out and come back to us.

I measured 2.3Ω on each. I took photos but I've been hit with the amazon rewards spinning wheel virus on my iPhone. Never had this happen. Apparently it comes from ads within the AK site. Do you need to see the photos?