Audio Power Output Module testing questions

[zenbrewer]

hello:
I have a sanyo plus-75 receiver i'm working on and i have been recapping the power supply board to remedy a fuse fault. seem to have narrowed it down to the Left power amp IC. the amp is an STK-0070 this is a picture of the power pack.
https://www.badcaps.net/forum/attach...1&d=1429452486

this is a picture of the schematic.
https://www.badcaps.net/forum/attach...1&d=1429452486

i have a meter with the capacitance setting and plan to remove and test the caps on this small board.
but how do i go about testing the IC itself?

thank you.

[popeye]

Re: Audio Power Output Module testing questions

The only way you can check the STK is in curcuit with vboltage supplied mesure the out puts and compare with the voltages shown on circuit dia.

[budm]

Re: Audio Power Output Module testing questions

You can check the resistance between Emitter and the Collector of the output transistors TR4, TR5.
There should also be two low Ohms resistors for the output transistors that you also need to check and see if they blown open.

[redwire]

Re: Audio Power Output Module testing questions

I test STK's (out of circuit) using diode-test and schematics of the internals. Usually, output transistors short or open or both. Here's a pic of the insides.
I have also seen shorts in the output STK's go back and damage the driver (i.e. STK3042/62/83) if your amp uses one. I also use diode test to find any faults there.

[Longbow]

Re: Audio Power Output Module testing questions

I have been recapping the power supply board to remedy a fuse fault. seem to have narrowed it down to the Left power amp IC.

Well, it seems you have found out why the fuse is blowing, and that would not be a shorted power supply capacitor. Naturally, replacing capacitors on the power supply board won't hurt anything, but why not go to the source of the problem (as you have now done)?

[zenbrewer]

Re: Audio Power Output Module testing questions

Well, it seems you have found out why the fuse is blowing, and that would not be a shorted power supply capacitor. Naturally, replacing capacitors on the power supply board won't hurt anything, but why not go to the source of the problem (as you have now done)?

Short answer: I am new to this

Long answer: originally I started by removing the leads from the power supply to the amp board and was still getting blown fuses. I tracked it down to the left channel's smoothing cap and some small ceramics along the same channel .. Figured if I was going to recap the left side should also do the right.
The entire repair attempt is here if you would like to read up on it and give me some pointers I would appreciate any help I can get.
http://www.electronicspoint.com/thre...-fuses.271229/

[Longbow]

Re: Audio Power Output Module testing questions

I can't follow your photo thread at all. It seems that your first issue was that one channel is out. Since the power supply is common to both channels, it is obvious that the power supply is not the problem. The first thing you do to any power amp that is minus one channel is to check the power output devices, since they are the most likely items to be shorted. In your case you have power modules. Just put your ohmmeter probes accross the output transistor pins (on the module) which are #2 and #3, and #8 and #9 if I read it correctly. If you see ZERO ohms, you know that the module is shorted. Before turning the amp on, check the other parts in the left channel power amplifier circuit to make sure that they are in good shape. Let us know the results after taking readings on the left channel module.

[zenbrewer]

Re: Audio Power Output Module testing questions

I can't follow your photo thread at all. It seems that your first issue was that one channel is out. Since the power supply is common to both channels, it is obvious that the power supply is not the problem. The first thing you do to any power amp that is minus one channel is to check the power output devices, since they are the most likely items to be shorted. In your case you have power modules. Just put your ohmmeter probes accross the output transistor pins (on the module) which are #2 and #3, and #8 and #9 if I read it correctly. If you see ZERO ohms, you know that the module is shorted. Before turning the amp on, check the other parts in the left channel power amplifier circuit to make sure that they are in good shape. Let us know the results after taking readings on the left channel module.

the left channel module read 0 to .3 Ohms across both output transistors.
the right channel module read nothing across both outputs.

the left channel module is short so i will need to replace.
I plan for the sake of balance to replace both the left and right.


is the right channel module indicating a fault with no reading across the outputs?

to my surprise i noticed that the right channel module is an STK 0080. the manual lists them both as 0070 so this must have been a repair.
can you recommend the ideal replacement modules?

thank you for your help

[stj]

Re: Audio Power Output Module testing questions

remove the left module and see if the right side still works o.k.

[stj]

Re: Audio Power Output Module testing questions

it looks like the best replacement is the STK0080-II

[zenbrewer]

Re: Audio Power Output Module testing questions

remove the left module and see if the right side still works o.k.

with the left module removed the fuse does not blow, but the right channel does not produce sound or indicate power via the LED indicators

[stj]

Re: Audio Power Output Module testing questions

unusual for both to fail!
maybe there is more wrong.

[zenbrewer]

Re: Audio Power Output Module testing questions

it looks like the best replacement is the STK0080-II

is this pin for pin compatible with the originals?

[stj]

Re: Audio Power Output Module testing questions

probably - i'll have to read the sheet more closely.
the difference between the 0070,0080 and 0100 is the power handling,
the mk2 versions seem to be improved as far as heat and noise/distortion is concerned.

[stj]

Re: Audio Power Output Module testing questions

btw, something i would be trying if i had one is using external power transistors to repair the module - just as an experiment.

[stj]

Re: Audio Power Output Module testing questions

o.k. i checked page2.
the mk2 not a dropin, the best to use is the STK0080

[zenbrewer]

Re: Audio Power Output Module testing questions

o.k. i checked page2.
the mk2 not a dropin, the best to use is the STK0080

thank you for your help.

most likely there are other things wrong, but i intended to continue down the rabbit hole until it works. its only a Sanyo and not really worth the money, but i'm just trying to learn

i will test things further down the circuit before placing my next parts order.

the manual lists the following components as part of the amp board.

VHF Coil
Semifixed Variable Resistor 1K
transistors
diodes
capacitors
and resistors

anything on that list i should look at first?

[stj]

Re: Audio Power Output Module testing questions

given it must be 30 years old,
check the caps (esr+capacitance)
and as for the fault - check the diodes and transistors.

have you got a schematic of this unit?

[budm]

Re: Audio Power Output Module testing questions

[zenbrewer]

Re: Audio Power Output Module testing questions

given it must be 30 years old,
check the caps (esr+capacitance)
and as for the fault - check the diodes and transistors.

have you got a schematic of this unit?

Yes.
Any tips on checking ESR and capacitance in circuit or should everything be removed first?

Have a cap meter .. Any low cost ESR meters out there?