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SAE Pre Drive Board (SAE 22-0091)

it’s been a spell since my last message so I thought I’d update. I finished installing all of the new components. However, on DBT, though the relay clicks the VU meters read very high despite there being no input and the heatsink in/around channel b’s drive board is gets overly warm/hot.

I’m trying to determine the bias but I doesn’t appear that adjusting the trimmers makes a difference so they might need replacing as well. The go-to seems to be Bourns (I replaced the trim pots on the pre-drive boards with Bourns). However I notice they didn’t quite fit the pcb ( they don’t come with the longest legs to feed through).

Are there any other brands/types of trimmers you’d suggest using?
 
I had one channel on a 2600 go way high on the meter. It was a short thru the insulator on the pre-drive board on one of the T0220’s.
I did have both drive boards on the 2600 get some components real hot and changed out brands and that stopped, they had ever so slightly larger diameter wire they used on the leads. Go figure.
Just use a single turn bourns, it’ll fit right in and adjusts just fine for the bias.
You have those bias transistors in contact with the heatsink ?
 
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When you say bias transistors are you referring to the to220s on the predrive board? None of them are in direct contact with the heat sinks and all of the passed the continuity testing I did. The specific replacements I used were onsemi mje15032G and 33G so I think those should be sufficient.

I’ll be getting some bourn single turns for the main board trim pot replacements and see if that can assist with the problem.
 
No, these are the little transistors on the mainboard that will contact the main heatsink from underneath. They would be right around where you would be putting the trimmers on the mainboard.
 
ok the TO-92s on the mainboard. I know they were originally in contact with the heatsink as there was thermal paste on the sink itself matching their location (six in all, three per channel).

I did replace those, reapplied thermal grease and believe that I put it at the right height but they might be too low. Given that you have to place the heatsink over of the mainboard it’s difficult to see if they’re in contact. Is there are way to make sure they are?
 
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jw68317 said:
ok the TO-92s on the mainboard. I know they were originally in contact with the heatsink as there was thermal paste on the sink itself matching their location (six in all, three per channel).

I did replace those, reapplied thermal grease and believe that I put it at the right height but they might be too low. Given that you have to place the heatsink over of the mainboard it’s difficult to see if they’re in contact. Is there are way to make sure they are?
Click to expand...
Grease up the tops and put the heatsink on. Then take it off and see if they all leave a "mark" or not. Then apply a glob on each mark and assemble or adjust any that are too low and do it again.
I just did this with a 3022 I'm working on. Best way I found to make sure anyway.
 
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