Autotek 7600 bts problems

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Disconnect the RCA cables from the amp and measure the resistance from the RCA shields to the speaker wires that are NOT used when the amp is connected in bridged configuration. You should read 0 ohms. Is that what you read?

What is the DC voltage measured directly across the speaker wires for each channel?

How much current does the amp draw when the output transistors are heating up?
I read open circuit. So, quattro can be the probblem?

Across each speaker wire I read 1,5 volt DC.

I don't know how much current the amp draws, but I'm using 2,5ampere 12.5 volt transformer. I think it's drawing 2,5amp, because the green amp led without tip 35/36 do more light

Thank you so much Perry! You're fantastic!
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Yesterday I tried to connect it in my car for any test. 2 minutes running at low volume and it comes in protection. Now I see no rail voltage: 11 irfz44 measure low resistance from gate to drain or source. What is the cause? Can be that I haven't installed Q201?

Now, what transistor I buy?
80 amp fuse

The amp had 2 problems: when I shut down amplifier, I eared a"bump" and after woofer oscillates a bit; when I connected left rca, with no music I ear periodic "tic" from woofer.

I thinked they couldn't cause problems, so I connected amplifier in my car, but running only left channel, because for the right channel I miss Q201. You can see it in my first post photo. Left channel has it (Q101) and it's a 2N5458, jfet...

If you want new photo I'll post it. Thank you!
Sorry. I didn't view the image full size. It's a muting transistor and should have no effect other than not doing it's job of preventing a turn on/off pop.

When testing any amp, you should use a relatively small fuse to help protect the amp in case there is a problem. A 20 amp fuse would have been enough to test initially.
A 20 amp fuse in the vehicle would likely have protected the Z44s.

What happened to Z44 #12? Did it survive? If so, that could mean that it had a bad connection on it's gate terminal which could have caused the others to fail.

Also, this amp and a lot of the early Autotek (and similar amps) have weak drive circuits. The drive circuit may not be driving the FETs correctly. This likely has a regulated power supply so you need to lower the voltage of the 12v power supply to force the pulse width to go as wide as possible. If the current increases when the supply voltage is reduced, the FETs are not likely being driven properly. It shouldn't be a problem with the Z44s but if it is, you'll need to modify the circuit to make it reliable.

I'm assuming that none of the output transistors or the rectifiers are shorted, causing an overload of the supply.
I think it's good, because I read higher resistence from gate to drain or source, but I don't know if it works good.

I'll verify if tl494 produces correct output.
Rectifiers and output transistors are all good ;)

Lower gate resistences can't be the cause? They don't modify gate to source voltage? Can I have suggestions (websites, topics) to make PWM circuit stable and working well for irfz44?
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If it reads more than 2x the gate resistor value, there is a broken connection somewhere.

The 494 is going to produce the correct output. The problem with the drive circuit will be beyond the output of the 494.

The lower gate resistors (compared to the originals) is necessary. It doesn't necessarily change the drive voltage. The drive voltage is essentially determined by the voltage on pins 8,11 and 12 of the 494.
I found bad connections.

Yesterday with only 2x irfz44 installed, I connected ampli in my car (this time with 20 amp fuse), only one channel. Sounds very very well, it produces a lot of power! After I tried it @ 2 ohm (2x Ciare CM200) with 25 amp fuse: more power, high quality! Fantastic!

Now can you help me with other problems?
1- When I turn off ampli, I still hear "bump" (only left channel connected, it has jfet installed).
2- Gain doesn't work
3- Treble and bass have never worked
Here's an old pic of the parts interested.


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