Testing STK0040-II ICs?

Currently fixing an old JVC JA-S22 amplifier. It came to me with two blown rail fuses and no relay clicking when the power button was pressed.

Lights come on when power button is pressed. On closer inspection I found it contained STK0040-II ICs. Upon replacing the rail fuses, I then powered up the unit and got the following voltages when testing each leg of the ICs:

Pin 1 = -1.2V
P2 = -35V
P3 = -0.02V
P4 = 0V
P5 = 0V
P6 = 0V
P7 = 0V
P8 = -0.01V
P9 = 0V
P0 = 0V

I presume from these readings that both of these ICs are blown (which I think would cause both rail fuses to be blown too) thus causing the amp to be stuck in protection mode.

The service manual doesn't have the voltages from the ICs displayed on the schematic. Does anyone know the sort of voltages you would expect to see on a working IC?
 
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That is a "Darlington power-pack" with a few additional components (Vb-e transistor+related parts). With the measurements you wrote down you can see, it is missing one of its supply voltages, so keep checking, there must be other failed parts in your amp beside the STK-s (fuse, resistor, etc...)
 

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Just measured resistance between pins. Results are the same with both ICs:

pin 8 and 9 = 236Kohm (red probe on pin 8, black on pin 9)
pin 8 and 9 = -165 k ohm (red probe on pin 9, black on pin 8)

pin 2 and 3 = -429 k ohm (red probe on pin 2, black on pin 3)
pin 2 and 3 = open circuit (red probe on pin 3, black on pin 2)

I think this confirms both ICs are blown. It certainly looks like the ICs were replaced at one point in the amp's life - (probably sometime in the 1980s?), as the soldering is untidy compared to the other stuff on the board, the heatsink compound looks like it was applied in a rush and I can see that the solder joins look newer compared to the other solder jobs on the board. Diode 403 didn't appear to be working properly when I took voltage readings from each side of the diode when amp was powered up and on diode check. I will be replacing this shortly.

Not yet found any other bad component apart from the ICs and D403.
 
"Just measured resistance between pins. Results are the same with both ICs:"

You need to borrow another meter and then switch your meter to 'diode test' and see how much voltage it puts out, the 'ohms' range won't check junctions.

I have an old meter that can put out 20V open circuit at 1mA, it can even test zener diodes up to 20V.
 
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A shorted output would have shown up with a resistance check (or diode check) and its not done.

You need to power the amp up with a bulb tester (to limit current in the event of a fault) and see what is happening. No speakers connected for any powered tests.
 
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I'll just add to that having looked at the circuit details further down the pdf that you should check the pinouts actually used. You will need to be sure that the extra connections on the II are not used (not connected) and so I'm going to change my recommend from a 'would be fine' to 'do a bit more research'.
 
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I was a little hasty in my first reply, however although the circuit appears fundamentally different that doesn't mean it wont work but you may need to do more research into it.

The II version has more options if the extra pins are brought into use, but leaving those disconnected and its essentially the same functionally.

As there is doubt, and unless you can find proof of the substitution working then it might be best to play safe and stick with the original fitment. That doesn't mean it wouldn't be OK, just that I can't guarantee it.
 
Hi guys I know is a very old thread but hey, has relevant information. I got a vintage JVC amp and I been troubleshooting the thing, someone had been in there before so i found several thing loose and some destroyed resistors. Then I found a couple of bad transistors checked diodes and replaced some caps, because the thing was half apart anyway, But I'm going around , finally got to the stk0040, someone had one out already, trying to get some information on them, i got here. I did the resistance check, then diode tes(short) and finally a voltage check(again).
P1-0
P2--37.7
P3-37.6
P4-0
P5-0
P6-0
P7-0
P8--.06
P-9-37.7
P10-37.7
so if I understand it correctly the thing is toast!!, thanks in advance for your help.
 
I just converted mine (STK0050) output to a Mosfet IRFP240/IRFP9240 pair with 6.8v Zener on Bias and it works for my SX-780. This chips are Hard to find now and most of the available on online stores are Fakes or relabelled. Darlington pair output can also be used but adjust the bias zener diode value or provide a suitable VbE spreader.