G-9700 F-3074 Driver Board Repair

[lambord]

I purchased a non-working g-9700. The seller said he sent 1 of the driver boards to a "professional" to have it repaired and when he got it back it still did not work.

I do not have much experience repair these but I got it at a fair price to if I can not repair it then I can part it out.

*Any test I'm doing so far is using a dim bulb tester*

If I remove both driver boards the unit powers on and relay clicks on
If I put in 1 of either board the unit will stay in protection mode with the flashing protection light
The original board has a resistor that starts to smoke (r20) when unit is turned on. The "repaired" board has nothing smoking but wont come out of protection mode.

My question is if I only have one channel driver board in the unit that is working properly, should it be able to come out of protection mode?

Trying to determine if I have at least 1 functioning driver board

 

[LBPete]

Put the boards aside for a minute and check the output transistors. That's often where the trouble starts.

- Pete

 

[lambord]

Put the boards aside for a minute and check the output transistors. That's often where the trouble starts.

- Pete

Im no expert but I removed all 8 and they all seem to be testing correctly after googling a bit on how to test them. All also look to be original and not replaced. But the thermal compound is a little messy, not sure if that looks factory to you or if someone has been in here already

 

[ivandezande]

That's normal. Now check all transistors on the amp boards.

 

[lambord]

The chart is what I am testing transistors with, let me know if this is incorrect please.


Results below are all the problem transistors I found

* Repaired Board *
tr05 (SA/PNP) - Collector to base diode drop (+ on base, - on collector has value .487)
tr06 (SC/NPN) - Base to emitter diode drop (- on base, + on emitter .486)
tr08 (SA/PNP) - Base to emitter open circuit (- on base, + on emitter OL)
tr09 (SC/NPN) - Base to emitter diode drop (- on base, + on emitter .280) and collector to base diode drop
tr10 (SA/PNP) - Emitter to base diode drop (+ on base, - on emitter has value .278)

* Original Board *
tr04 missing. I purchased KSA1381ESTU transistors from Mouser for a replacement of tr04 but have not installed it yet because I am not confident it is a like for like replacement
tr05 (SA/PNP) - Emitter to base diode drop (+ on base, - on emitter is reading .483v). Also comparing the two board this transistor is in different holes than repaired board. The original board labels are off from where transistor actually is, maybe repairman was just following the board labels?



tr06 (SC/NPN) - Base to emitter diode drop (- on base, + on emitter reading .483v)
tr09 (SC/NPN) - Base to emitter diode drop (- on base, + on emitter reading .280v)
tr10 (SA/PNP) - Emitter to base and collector to base diode drop

 

[LBPete]

Don't trust the markings on the board. Look at the schematic and determine what each leg of the transistor connects to. Then determine the positions of those terminals on the transistor you are using and match them up. You need to remove the transistor from the circuit to check it with an ohmmeter.

- Pete

 

[lambord]

Don't trust the markings on the board. Look at the schematic and determine what each leg of the transistor connects to. Then determine the positions of those terminals on the transistor you are using and match them up. You need to remove the transistor from the circuit to check it with an ohmmeter.

- Pete

I think the board markings are incorrect like you were saying. Repaired board had it in the wrong spot. I will remove and test transistors


Thanks