Kevin's Hafler p-500

[mlucitt]

The do hickey is the only thing I've fount that will test those Hafler FETs. It seems like you have to test vintage devices with vintage test equipment. That means that the doctors Lee and I go to use an old mercury thermometer, you know where, to see if we're healthy.

 

[jbeckva]

Boy is THAT a visual I could have not stood to see...

 

[kevin]

I think I'll shut up and watch the race.... lol

 

[laatsch55]

Drags??

 

[kevin]

Nope....Nascar... I thought dale Jr. might pull this one off..... But he didnt..

 

[mlucitt]

So my school work has been getting in the way of enjoying the pleasures of life lately so I put it on the back burner for awhile. My first priority is Kevin's P500. I pulled all the power MOSFETs and found one that seemed "iffy". Research shows that MOSFETs can fail dramatically (like an internal short or open) but most of the time one of several internal uni-junctions fails. This means the device "may" test fine, but only breaks down under (1) power or (2) a combination of both power and load. Joe, have you seen this?

Anyway, using a polarized gate-on, gate-off test, I was able to identify one bad N-channel device in the right channel. My question is should I replace the bad device, all the devices in the channel/phase, replace them one by one (like in a PL with power transistors), or something else? I was never able to find a cause for the blown device, it might have been overload, but the Hafler is pretty robust and has a good over-protect circuit. My thought is that this one was the weak link and just let go, which is contrary to what I have been told - that MOSFETs are very strong.

Thoughts?

Mark

 

[kevin]

I just cant believe you did'nt get any THOUGHTS.... LOL..... I just knew when I logged on this morn That You, Joe, Lee, and several others would have this thing up and running..... Wish I could help.... Im the one that got it in the shape it's in...

 

[mlucitt]

Kevin do you remember what the situation was that led to the original condition? Outputs crossed, speaker fried, an earthquake, etc? The situation could help explain the mode of failure... It was only the Right Channel that failed. Could be that it just gave out and the power level was not a factor. Maybe it was an overheated device?

So far I have not found a reason for the failure, I would hate to get it fixed, test it, test it, test it again, and then send it back to you and see it fail again because of a resistor that only fails when Jimmy Buffett is playing (listening to that now).


Thanks,
Mark

 

[kevin]

Mark... I really dont think anything led to the problem.... lol... One day the right channel just stopped working at low volume. I did have that amp in my system when I was single..... I PLAYED IT LOUD ALOT. It would shut off two of three time a night.... I even had fans on it... As long as i played it about half way it was ok... Then when I would turn it down it would be ok for about two or three min. then the right side would go out again... When ya turned it back up loud the right side would come back... Wish I could be more help...

 

[Fairchild]

I have a P-500 that sees hard loud play and I have never had a channel drop out on it, mine has a fan from the factory, your p-500 should too.

Jim

 

[mlucitt]

Yes, this P-500 has a fan. I am glad to hear that the Right Channel dropped out at low volume, that indicates a soft failure mode. Harder to troubleshoot but easier to fix once the problem is found. It could be a simple thing like a cracked solder connection or a loose wire. I'm on it.

BTW, the spectacular failures are the most fun to fix, smoke, burnt, melted, fried, etc.

Thanks,
Mark

 

[kevin]

LMAO.... Yea... I know thats what you wanted to hear but it just didnt do that.... It had a real soft mild break down..

 

[kevin]

O-yea Mark.. Something else I remember.... The other one I have did the same thing.... I had them both put up for over a year... When I got them back out and hooked the one I have back up it played fine for a few days.... even at low volume.. Then out of the blue it started the same ole thing.... right side out at low volume... When It did that is when I downed it and sent you all the little round shiney hickeys out of it...

 

[kevin]

Hello Mark !! Did you replace that ''iffy'' MOSFET ? I know you said the other day you were playing it ! I'd say you have fixed it !

 

[laatsch55]

Kevin-------- you have been WOPL'd, son there is NO going back. If would be a wasted and fruitless trip.

 

[kevin]

O I know that... I got in mind using this Hafler on my Sub.... I LOVE MY PL'S.....

 

[laatsch55]

Subs, schmubs. Get a real speaker!!

 

[kevin]

LMAO.... You get off my shitty speakers right now !!!!! A Sub is how us poor people get bass !!!!

 

[laatsch55]

Ah, I shouldn't speak ill of things I haven't heard!!!

 

[kevin]

But your right.... If your speakers were right you wouldn't need a Sub !! Im looking forward to hearing those baby K-horns that Sutton is building... I can't think of the name of em... Thats what i call em !!!