Outlaw Repair

[ETK]

Hey all I'm working on getting a clean outlaw up and running but have run into a issue on the m100 side. First off I have already replaced all the ps caps with Panasonic HF 16v 5600uf. Problem is amp powers up fine with solid green light and 1.5 amps current draw but there is a audible hissing/buzzing coming from somewhere on the board. That's with no speakers or input connected. The board shows no sign of anything burn't or other caps overheated and no fets are shorted. Now I never powered up the amp before changing the caps because the old ones were leaking so I don't know if the amp previously had this issue. Anyone seen or heard of something like that? I really appreciate any insight/direction from any of you and I could upload pics of the board if needed. Thanks Evan

[ETK]

Had some time this morning to look at the amp again and the hissing seems to be coming from resistors R42,R42A,R43 and R43a. They are original and all test fine at 160 ohms and have continuity through the board. When powering up the resistors get real hot very quick. Sounds kinda like they're sizzling. Do any of you think it would be a simple as swapping the resistors or something down the chain causing them to rapidly heat up? I'll be ordering new resistors this week from digikey.

[Eric D]

It is normal for these 4 to get hot...



You can replace them with larger versions (which will help), but they will still probably get quite hot.

I am pretty confident the sound you are hearing is not from the resistors, but instead the power supply transformer right next to them. In the past I have had to coat transformers in epoxy to keep them from hissing so bad. It might work in your case as well.

[ETK]

Hi Eric thank you for taking the time to reply. I think your right in that it's the transformer making the noise. What kind of epoxy would you recommend to cover it and where would you apply it? I will go ahead and replace the resistors with larger versions and do the epoxy and see where that gets me. Here is the amp in question. Evan

[trickyricky]

Those resistors are already 5watt rating, anything higher and you might have a hard time fitting them properly as the 10watt resistors are 2" in length.

[ttocs]

try tightening down the connections at the ends and see if it helps.

[Eric D]

I use 5 minute epoxy, but I would think a slower setting epoxy would be better. Something slow could better seep into the windings and onto the core of the transformer. Keep in mind you don't want it leaking right on through and getting all over the board. I paint the epoxy all over the transformer. So long as you are using something clear it does not make it look too bad, or even that noticeable.