Earthquake PA4300 help needed.

marko

Member
2004-05-08 11:40 am
donnyuk
Hi all, got a big project on here and having a little trouble with the amp stuck in protection.. I'm working on the main half of the amp at the moment as this has the front end and the other half has been removed for simplicity (hope this is OK to do).

amp turns on then after about a second goes into protection and draws very little current about 0.02amp or less.

TL594

1: 180mv
2: 4.9v
3: 4.9v
4 16.8mv
5: 1.5v
6: 3.46v
7: .6mv
8: 13.7v
9: .2mv
10: .4mv
11: 13.7v
12: 12.7v
13: 5v
14: 5v
15: 5v
16: 10v

only other thing to note at this point is 2 of the pots are missing on the front end but wouldn't of thought this would stop smp going into protection?


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marko

Member
2004-05-08 11:40 am
donnyuk
I managed to get it out of protection! I removed the 6 irfz44n's and they checked out OK, it was still in protection so removed the rectifier and it powered up. the rectifier appears to be fine but not sure how to check it correctly, maybe the transformer has a short on that side?

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These amps have an awful drive circuit. It doesn't generally cause a problem because the supply is regulated and as soon as the target rail voltage is reached, the duty cycle is rolled back. When the duty cycle is full, the amp has shoot-through for the PS FETs and they overheat. That could be the cause of the overheating here. With the rectifier out, the amp is increasing the duty cycle to try to reach the target voltage but cannot.

When you push down on the top of the bulging cap, do you feel resistance or does it easily flatten and pop back up?
 
Did the rectifier test OK?

Can you check to see if the amp will produce audio (powered up for only a few seconds unless you clamp everything down tightly)?

This amp has a multi-stage supply (if it's like the 2300) so I think it may produce audio with the large rectifier out of the circuit. Confirm that it has supply voltage on the power supply pins of the op-amps in the preamp section if you have no audio.
 

marko

Member
2004-05-08 11:40 am
donnyuk
the rectifier apeears OK out of circuit, having said that I've only tested it for shorts. as soon as I put it back in circuit the amp goes into protect.

it's basically a 2300 and it even says that on board, then it has a slave on the other half, front end is taken care of by the main unit.

testing for audio may be a little tricky just yet as it's missing a gain pot and one of the tone control pots as well, I hope to order these asap as soon as I find the a close match.