Yamaha CA-2010 stuck in protection help

[quadmatrix82]

I can confirm it I will desolder the board and take a photo but it’s certainly like that

 

[Nashou66]

First off always clean the solder side of the board your working on with Denatured alcohol so your able to see more clearly between
solder joints as the old solder flux and moisture barrier inhibits a clear view.

After you will be able to, and as will others via pics, if there is anything bridged or any cold solder joints.

Athanasios

 

[quadmatrix82]

First off always clean the solder side of the board your working on with Denatured alcohol so your able to see more clearly between
solder joints as the old solder flux and moisture barrier inhibits a clear view.

After you will be able to, and as will others via pics, if there is anything bridged or any cold solder joints.

Athanasios

Thankyou I uploaded some additional photos

 

[mbz]

Photography is not great, assume you've inspected for solder bridges under magnifying lamp. Following looks iffy

 

[mbz]

Ok I had a look here are the measurements
+b 8v
-b -7.5v
Tp2 -4.5v
tr319b-3.1v
Tr319e -3.95v
Fr306 3.7v
tr320b -8v

Standout is Q320b -8V abouts -B, -B1 rails.
Also voltage between Q319b and Q320b is 5V, target is 2.5V abouts.

Looks like a transistor on the -ve rail is flooding the output stage with -ve voltage.
Candidates are TR310 and TR318 and D308. Any of these parts not already replaced?

Measure TR310, TR318 b/c/e voltages and D308 anode/cathode, looking for standard Vbe=0.6V
and not Vce = Vce(sat). Also diode Vf(anode/cathode) = 0.6V

These appear to be the last sensible suggestions.
Maybe TR310 in saturation, measure b/c/e voltages
Maybe TR318 failing short c-e again b/c/e
Maybe D308 failing short, measure anode/cathode voltages (wont measure 0.6V)
Doubtful D304 open would cause, measure anode/cathode voltages

 

[quadmatrix82]

Photography is not great, assume you've inspected for solder bridges under magnifying lamp. Following looks iffy

Confirmed no solder bridges that must be have been a bit of lint or tissue after cleaning the board.

 

[quadmatrix82]

These appear to be the last sensible suggestions.
Maybe TR310 in saturation, measure b/c/e voltages
Maybe TR318 failing short c-e again b/c/e
Maybe D308 failing short, measure anode/cathode voltages (wont measure 0.6V)
Doubtful D304 open would cause, measure anode/cathode voltages

I will check these, the board has all new diodes, transistors with the same fault as it had on first inspection. I also compared every resistor in circuit with good channel as another check and found nothing a miss.

Will report the voltages once the board is resoldered and fitted again

Is it possible the FET is problematic?

 

[mbz]

Is it possible the FET is problematic?

Yes.

Problem is visible at Q320b etc but root cause could be anywhere in the chain back to the fets.

 

[quadmatrix82]

Ok I’m revisiting this, having all new transistors and diodes on the board and I can only suspect the 2sk99 is a potential culprit, I have sourced matched 2sk170 to test the theory but not sure on the pinout is this correct based on the photo? The 2sk170 pin out is d-s-g but I couldn’t find a pin out for 2sk99 and the readings were the same using a meter across pin 1,3 even when reversed.

The second photo shows the original pin out for the FET ? Thanks

 

[quadmatrix82]

Does anyone have a data sheet for 2sk99? I couldn’t find anything online

 

[quadmatrix82]

Here is the pin layout with pin one on the far right for anyone that is interested in future - amp up and running