Yes, tinned the fets and the board, and soldered them just like you suggested. On some others I used extra solder on the mehsa pads to get a little squeeze out so I knew they were fully set/seated. I'll try to radius the leads in the future.
I should see equal voltage at R5 & R6 then?
Any insight about the bias? Do you happen to know a part number for the bias pots on these?
I should see equal voltage at R5 & R6 then?
Any insight about the bias? Do you happen to know a part number for the bias pots on these?
The two resistors are the pulldown resistors for the power supply drivers. Their voltages should be very nearly identical.
The pots are standard Piher pots. Mouser should have them. That said, I've never seen a bad one that wasn't physically damaged.
If you set the bias significantly higher. do you lose 100% of the bias when you push on the board?
The pots are standard Piher pots. Mouser should have them. That said, I've never seen a bad one that wasn't physically damaged.
If you set the bias significantly higher. do you lose 100% of the bias when you push on the board?
As long as the insulators are clamped and heatsink compound applied, you can go quite a bit higher. 1/2 amp increase in idle current is perfectly OK. Just watch the idle current to make sure that it doesn't avalanche.
A problem that I had once was the bias transistor shorting to the edge of the insulator. Make sure that that's not an issue.
A problem that I had once was the bias transistor shorting to the edge of the insulator. Make sure that that's not an issue.
Hi Perry,
Sorry for taking so long to get back to this. I pulled this board back out tonight and initially had distorted/crackling output on the same channel that was giving me bias trouble. Attempting to adjust the bias gave no change in current draw or cleaner output. I sprayed the bias pot with some Deoxit Fader F5, and that seemed to help as I now get positive adjustment.
I was still getting small changes in the current draw and some popping & crackling output when pressing on the board. I flipped it over and found some residual cotton swab fibers leftover from cleaning flux after replacing fets/etc. I cleaned that all off and now it seems to be working and maintaining the bias even when pressing/flexing the board. Seems like some flux soaked fibers were causing some conductive bridges between some components - do you think it could be that simple?
R5 & R6, along with the TL494 still getting warm/hot. I'm just judging this by touch - R5 & R6 getting hotter than the TL494. I can hold my finger to them continuously, but I would say they are getting close to uncomfortable. Do you think this is normal? Anything else I can/should check? I can probably compare to another 800a2 board if that's my best option.
This is the bias pot - is this a Piher? I know some of the others have Pihers similar looking to the gain pots, but I can't find these. The only markings are a subscript N, 202, subscript X.
Thank you for your help. I also have a 600a4 I'd like to ask some questions about if you're knowledgeable about those as well.
Sorry for taking so long to get back to this. I pulled this board back out tonight and initially had distorted/crackling output on the same channel that was giving me bias trouble. Attempting to adjust the bias gave no change in current draw or cleaner output. I sprayed the bias pot with some Deoxit Fader F5, and that seemed to help as I now get positive adjustment.
I was still getting small changes in the current draw and some popping & crackling output when pressing on the board. I flipped it over and found some residual cotton swab fibers leftover from cleaning flux after replacing fets/etc. I cleaned that all off and now it seems to be working and maintaining the bias even when pressing/flexing the board. Seems like some flux soaked fibers were causing some conductive bridges between some components - do you think it could be that simple?
R5 & R6, along with the TL494 still getting warm/hot. I'm just judging this by touch - R5 & R6 getting hotter than the TL494. I can hold my finger to them continuously, but I would say they are getting close to uncomfortable. Do you think this is normal? Anything else I can/should check? I can probably compare to another 800a2 board if that's my best option.
This is the bias pot - is this a Piher? I know some of the others have Pihers similar looking to the gain pots, but I can't find these. The only markings are a subscript N, 202, subscript X.
Thank you for your help. I also have a 600a4 I'd like to ask some questions about if you're knowledgeable about those as well.
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The resistors are likely contributing to the heating of the 494.
I can't remember ever having to replace one of those bias pots. This is the number from a Rockford parts list.
(PIHER # N6L30T3N-202)
If you can't find it, try contacting the forum member seankane.
If you have questions about a different amp, start a new thread for it.
I can't remember ever having to replace one of those bias pots. This is the number from a Rockford parts list.
(PIHER # N6L30T3N-202)
If you can't find it, try contacting the forum member seankane.
If you have questions about a different amp, start a new thread for it.
Yes. Normal? I don't really know if it's normal but if the resistors are within tolerance, I'd think it's normal/to be expected.
Connect only remote and ground. Do you see any heating from the 494?
Remember, what's somewhat uncomfortable to touch is essentially icy cold to most electronic components.
Connect only remote and ground. Do you see any heating from the 494?
Remember, what's somewhat uncomfortable to touch is essentially icy cold to most electronic components.
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