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Old 07-10-2019, 12:00 AM   #1
Amraks
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Default Quest QA3004 - suspected blown output stage

First time really working on a amplifier.

Symptoms where
person plugged in on the outputs.
4 output stage fuses died.
They put in another set of fuses and only 2 on one side died this time.

Upon my inspection I have found water on the side that killed the 2 fuses the second time.
I have included pictures of little pool of water its hard to know how much water has been in this as I found some on a few mosfets as well.

I am not sure if my in circuit transistor tester(jaycar or dicksmith) is capable of testing these transistors.
as I have used it and they are all reading short on both channels.

Desoldering one of the resistors from the base of transistor apparently make for easy testing the transistors.

What should I be looking for when testing these?
Attached Images
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Old 07-10-2019, 01:51 AM   #2
andy1
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Default Re: Quest QA3004 - suspected blown output stage

You could try using a hair dryer and get rid of the moisture before powering up.
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Old 07-11-2019, 02:11 AM   #3
Amraks
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Default Re: Quest QA3004 - suspected blown output stage

I will have to try that.
I just hope they haven't switched it to bridge mode with a load under 8 OHMS
as it says in the books it will blow the A side.
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Old 11-16-2019, 06:38 AM   #4
Amraks
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Default Re: Quest QA3004 - suspected blown output stage

I am having a crack at this amp
Found 2 Blown Transistors on the A Side
Found 9 blown Transistors on the B Side

Now my question is if I have cleared all these shorts would I adjust bias 1 side at a time
So do A side first
then B side

would I need to turn down the bias first?
Would I need more than 1 multimeter for negative and positive side to balance the bias?

Last edited by Amraks; 11-16-2019 at 06:51 AM..
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