bostwick da1200.1hc problem

[ampjunkielikeme]

when i give the amp a hot and a ground , it does nothing... when i hook the remote wire to it, it pulls a constant 20 amps of juice from my power supply... the power supply transistors get rather hot...

the amp does not power on at all...it doesnt have a protect light, just a green led that does nothing...lol

actually i have 2 of these amps doing the same thing...

i replaced the hip chip to no avail... changed the power supply transistors and gate resistors...does the same thing...

the transformer doesnt have a short in it...

ive tested the gate drive transistors, and they are reading two reading of 0.678v , so they test good...

ive changed out the tl949 pwm ic chip.....still pulls 20 amps....

ive taken out the rectifiers. it still pulls 20 amps

the outputs and not shorted.....
ive pulled all the caps on the power supply side, they are good...im going to pull the others near the outputs next..

what is the black rectangle thing in the middle of the amp? it has a row of 8 or so pins right under it....

...

pics:

[Perry Babin]

If it only pulls current after remote voltage is applied and it pulls current with the rectifiers out of the circuit, it likely has either a defective drive circuit or a shorted transformer.

How did you check the power transformer to determine it wasn't shorted?

While the power supply FETs were out of the board, you should have checked the voltage on the gate pads for the PS FETs. If you pull the FETs again to check it, it should be ~5-6v DC on all of the PS FET gate pads.

The black box is the protection module.

[ampjunkielikeme]

i checked for continuity from one side of the transformer to the other....
and if i put just a hot and a ground to the amp , i dont see any voltage on the secondary side..

is there another way to see if the transformer is shorted?

i took the ps fets back out , and i have 5.99v on the gate resistors..

[Perry Babin]

Checking from primary to secondary only tells you if it's shorted from primary to secondary. If you have windings shorted from primary to primary, the meter won't show it. You either have to ring it (with an inductor ringer) or you have to drive it with a known good driver circuit.

Do you have the same DC voltage on 'all' gate pads for the PS FETs?

[ampjunkielikeme]

yes, all the gate pads have a good 5.9 voltage

[Perry Babin]

Do you have a large (20 watts+) 2 ohm current limiting resistor?

[ampjunkielikeme]

no i dont.... are they the big white tall square resistors?

[Perry Babin]

They can be any shape. Tomorrow, go to Radio Shack and buy 4 of the 271-120. Connect them in parallel.

Reinstall the FETs and clamp them to the heatsink. Connect the paralleled resistors in series with the B+ line feeding the amp.

Power up the amp and twist (push, pull...) the transformer. if it's intermittently shorted, the voltage will be dragged down when it's shorted and will go up to ~12v when the short is broken (when you twist the transformer).

[maydaydeejay]

It seems like an another relay, but this one is for output voltage from inverter.
The "main" relay is located near speaker output... and really this black thing looks like one of them to me.
It may B poss that it has some shorts or so.

regards
mark

[ampjunkielikeme]

i got the resistors...

after twisting and pulling on the transformer , the amp powered up and started producing sound..

both of the amps had shorted transformers...it must be a bad design or something...

what do i need to do to the transformer now that i got the short out? will clear epoxy work to keep it from moving around again?