250 hcca grounded out problem

[mcgyver24]

Parts have been orderd. I'll let you guys know how it turns out. Thanks again for all your help!

[mcgyver24]

Ok, so I replaced all the parts in YELLOW in the attached picture. And retested to the best of my ability the circled parts in BLACK again. After test it seems I still have a problem. I have not yet powered it up because I feel it will cause more damage.

Results....

The ohms reading on all the 3205 seems be good now (~84 ohms) on all of them both sides.

But the 3205 seem to have continuity between all of then and pins 1&3, 2&3, & 2&1. Is this normal?

There seems to be a really high resistance between the positive and negative power terminals. This is not normal in my opinion.

So now I stuck. Any ideas an what to test and or replace next?

Thanks for your help, Sean

[Perry Babin]

But the 3205 seem to have continuity between all of then and pins 1&3, 2&3, & 2&1. Is this normal?

**** How many ohms?

There seems to be a really high resistance between the positive and negative power terminals. This is not normal in my opinion.

**** Initially, an ohm meter will read relatively low resistance but the readings will increase as the capacitors charge. This is normal. If there was low resistance all of the time, the amp would constantly draw current from the battery.

[mcgyver24]

I get a reading of ~84 ohms between each 3205 on the two outer pins (1&3). Is this normal?

Should I try to power it up?

Thanks,

Sean

[Perry Babin]

I'd expect to see ~110 ohms. They typically use a 100 ohm pulldown resistor but maybe they used a 75 ohm resistor in this amp. Do you see a 75 ohm resistor that's connected from the non-gate side of the gate resistor to ground?

You can power it up but clamp ALL transistors tightly to the heatsink and insert a 15 amp fuse in the B+ line.

[mcgyver24]

Perry,

So I put everything back together and tried to power it up. It blew a 10 & 15 amp fuse. I have about 120 ohms between the positive and negative power terminals. I don't think this is normal.

Can you please provide a picture to your question, "Do you see a 75 ohm resistor that's connected from the non-gate side of the gate resistor to ground?".

I think my reading of ~84 ohms on the 3205s is normal on pin 1&3 because I get the same reading on my working amp.

So now I really stuck. Not sure what to do next. Please help.

Thank for your time,

Sean

[Perry Babin]

Unplug the RCAs from the amp and measure the resistance across the power terminals (disconnected from 12v power supply). Do you still read 120 ohms?

[mcgyver24]

Yes, 120 ohms.

[Perry Babin]

What is the resistance from the B+ terminal to the RCA shields (input and output shields).

[mcgyver24]

305 ohms from the power pos+ terminal to RCA shields.