Problems with Onkyo Integra A-8067

[niss_man]

Hi all

I recently (a few months ago) purchased a 2nd hand onkyo A-8067 which wasn't working for $25 on EB to see if I could have a go at fixing an old amp and now need some help in fault finding it.
What I found when opening it up was that the 2 main power caps had oozed gunk everywhere onto the pcb and also found a couple of main power transisters blown on the right channel. These were replaced with new ones and the amp sprung into life again. Sounded great when it was working I must say. It has been used for about a month of moderate listening before deciding to pop the main fuse again.
On checking the power transistors again it seems that the right channel has one(or some) transistors shorted again.

I was wondering if someone more knowledgable than myself may know what the problem might be or point me in the right direction as there is obviously something causing the transistors to go caput. Maybe someone knows some common problems with these Integra amps???
I can't attach the schematic as it is 760kb in size but you can get it from HiFi Engine | Download Free User/ Service Manuals, Amplifier, Receiver, CD, Tape, Tuner, Video under the manuals section. A truly great site many have probably seen already. I can send the schematics via email if anyone wants it. Any help would be greatly appreciated.

P.S. Found another dl link here http://www.eserviceinfo.com/download...yo_A-8067.html just click on the download bit near the question mark half way down the page.

Regards

SImon

[currentflow]

Hi niss_man,

I presume you have thoroughly cleaned the electrolyte from the PCB where the capacitors had leaked. Have you checked for dry joints?

Regards currentflow

[Tekko]

Shorted outputs usually mean more broken parts down the line such as the drivers and maybe also VAS.

[niss_man]

Originally Posted by currentflow

Hi niss_man,

I presume you have thoroughly cleaned the electrolyte from the PCB where the capacitors had leaked. Have you checked for dry joints?

Regards currentflow

Yeah cleaning was done transistors replace and it lasted about a month. I have had a half **** attempt at searching for dry joints and will do so in more detail when I get time. I think I have read somewhere that the zener diodes can go in these amps?? What is the method to test a zener?

[niss_man]

Originally Posted by Tekko

Shorted outputs usually mean more broken parts down the line such as the drivers and maybe also VAS.

I've checked all transistors and apart from the blown power transistor ones they seemed ok.

Regards

Simon

[currentflow]

Originally Posted by niss_man

Yeah cleaning was done transistors replace and it lasted about a month. I have had a half **** attempt at searching for dry joints and will do so in more detail when I get time. I think I have read somewhere that the zener diodes can go in these amps?? What is the method to test a zener?

Generally, you can measure the voltage across a zener diode in circuit to verify it is within parameters. The 'banded' or 'striped' end is the cathode and this will be positive with respect to the anode. That said, there doesn't appear to be any zener diodes in the critical parts of the circuit which could have caused the fault you reported.

Presumably, the output protection relay, RL701 saved your speakers when the fault occurred.

I would be tempted to start by replacing the known failed transistors, disconnect the loudspeakers and power up briefly using a suitable light bulb in series with the mains supply. Continue to check and follow the procedure for the idling current adjustment on page 4 only if the bulb doesn't glow brightly.

Measure the various test point voltages as per the circuit diagram, comparing against expected values for dotted areas marked NADA-2286 and NAMA-2157c as well as their opposite channel counterparts.

Stop if anything gets excessively hot during the above...

Hope that helps,
Regards currentflow

[niss_man]

Test points (The rectangles with arrow and number inside). Gee I must be blind. I can see heaps of test points on the NAMA-2157 section now. I can't see any test points on the NADA-2286 section though. Sounds like an excellent way to start my fault finding. I will definitely use the test points shown as a help this time to try pinpoint the failed area.

Unfortunately will have to wait for more transistors to be purchased before starting though.

Regards

Simon

[currentflow]

Originally Posted by niss_man

Test points (The rectangles with arrow and number inside). Gee I must be blind. I can see heaps of test points on the NAMA-2157 section now. I can't see any test points on the NADA-2286 section though. Sounds like an excellent way to start my fault finding. I will definitely use the test points shown as a help this time to try pinpoint the failed area.

Unfortunately will have to wait for more transistors to be purchased before starting though.

Regards

Simon

You're right, while they are not test points specifically, they are "places with expected voltages present"

Good luck!

Regards, Steve (currentflow)

[currentflow]

Originally Posted by niss_man

...
I can't see any test points on the NADA-2286 section though.
...

The service manual I was referring to was from your second link in post #1. I've just counted around 30 in this manual within "NADA-2286". If they are not marked on the board, just follow the circuit component references.

Regards, currentflow