250 hcca grounded out problem

[Perry Babin]

Did you use the same 3205?

Measure the resistance from 1-2 to see how many read near 0 ohms.

 

[mcgyver24]

No I used the new one. It was working untill I put everything back together and fliped it over. Then everything happen.

 

[mcgyver24]

Just pulled the 3205 out. Its bad I get resistance between 1 & 2.

 

[Perry Babin]

What about the rest in the board?

 

[mcgyver24]

Everything looks ok but I have not check with my meter. How do I check the A06s and the A56s with my meter. Before I just replaced them all. Now I would like to see what if any are bad.

Thanks,

Sean

 

[Perry Babin]

Check the power supply FETs to see if any read near 0 ohms (1-2, 1-3, 2-3). If none do, clamp everything and power it up through the 15 amp fuse.

If it powers up, twist, push, pull on the power transformer to see if it causes the fuse to blow.

 

[mcgyver24]

Perry,

So I powered it up and works and sounds fine, GREAT!. I then pull, twisted, and pushed on the transformer. The fuse did not blow. I just want to make sure that the transformer is the thing with the 4 wire I desolder and solder a few times, right? What should we do next?

Thanks again,

Sean

 

[Perry Babin]

Yes, that's the transformer.

I'd put it back together and reinstall it (with two 15 amp fuses instead of 30s) leaving the FET that you replaced out of it. If it works for days or weeks, it could indicate that there's an intermittent connection the gate resistor, or on the gate pad or a trace on the gate circuit for that FET. If it blows the fuses again, there is another problem.

 

[mcgyver24]

Perry,

I forgot to mention that I already replaced the bad FET before the latest test.

 

[Perry Babin]

Well... you know what to do next time.

 

[mcgyver24]

Perry,

When putting it all back together I noticed that the 2 large caps actually touch the sliding bottom cover. This might make the board bend a mm or two. Plus 1 cap has a soft top on it. The other is hard. Please see the attached picture. Should this be something to worry about?

Thanks,

Sean

 

[mcgyver24]

Perry,

Also, that 1 cap when apply pressure to its side or push it, it makes a clicks noise. Dose that mean anything?

 

[Perry Babin]

It's just a plastic insulator. The clicking doesn't mean anything.

Look at the area of the bottom cover that is just above the transformer. Does it show any signs of making contact with the transformer windings?

 

[mcgyver24]

Perry,

The only thing that makes contact is the 2 large caps. Eveything else is much lower.

Thanks,

Sean

 

[mcgyver24]

Perry,

I put all back together again and now it dosen't work again, its blew a fuse. I measured the 3205s and none of the pins equal close to 0 ohms. I really think its those caps. How can I test them. I used to get 1.5 M ohms at B+ and ground when it worked and now its around 200 ohms. Could the caps have anything to do with this?

Thanks,

Sean

 

[Perry Babin]

While I guess you can't completely rule out the capacitors, I really doubt that they're at fault. If you don't have an iron that's up to it, you risk damaging the board in a way that may be difficult to repair properly.

Is the FET that repeatedly blew still in the circuit? If so, does it read slightly lower than the rest of the FETs (1-2)?

 

[mcgyver24]

Perry,

I really can't get a good reading for some reason. When I read 1 & 2 it goes up then down from the low 100s to M and then K. This happens on all the FETs on the power side. Not sure why it is doing this. The output side gives my a constant reading. I don't think is my meter. Any ideas?

Thanks,

Sean

 

[Perry Babin]

The changing readings are typically from various capacitors charging and discharging.

If all of the power supply FETs read 100+ ohms from 1-2, they're likely OK.

 

[mcgyver24]

Perry,

Yes, all of the power supply FETs read 100+ ohms from 1-2.

What else could I cheak?

Thanks,

Sean

 

[Perry Babin]

Will it blow the fuse if you power it up?