Hartke HA1200 main board removal

[bassliner]

My beloved Hartke Kickback 10 (120 RMS Watts) was in an accident and the mid control knob in the EQ section has been sheered off. The schematic shows It is a 50K (linear taper) potentiometer ( VR104 ). I have had training and experience with soldering, schematics and circuits in general. I use this little amp all the time and want to replace that pot. Looking at the amp assembly leads me to think removal of the main board where that pot is mounted will be very difficult to remove because the power transistors are mounted to a heatsink and there is no obvious clearance to remove the circuit board from the steel housing assembly. Has anyone removed this board in order to perform service? Any advice would be greatly appreciated. I do not want to pull it apart, only to cause more damage....thanks..Roy

[DrGonz78]

Some members here might have direct experience on exactly how to remove the preamp board and what steps to take for that amp. The other members could benefit from a picture of the inside of the amp. A picture says a thousand words. You are probably going to have to pull out the power module a bit to make it easier to remove the preamp. Don't force it through a tight space.

[g1]

The other members could benefit from a picture of the inside of the amp. A picture says a thousand words. You are probably going to have to pull out the power module a bit to make it easier to remove the preamp. Don't force it through a tight space.

Yes a picture will definitely help. On some amps the heatsink can be separated from the main chassis. If this is the case the output transistors will not have to be separated from the heatsink.

[Jazz P Bass]

All of the knobs & nuts get removed.

The heatsink screws, that hold it to the chassis, also get removed.

[Enzo]

I have repaired a few of those, and I don;t recall anything out of the ordinary in disassembly.

[bassliner]

Thanks, Gentlemen. The deed is done. It required the usual disassembly, but it also required me to spread the steel chassis very wide in order to remove the preamp board. I had to clamp the chassis to my work bench and bend severly with slip joint pliers just to clear the board for removal. Once the board was removed, I desoldered the broken 50K potentiometer and replaced it with a new one of the same spec, but a different physical profile making it necessary to run 3 jumper wires down to the pc board to make the connections. Tested fine afterwards and cosmetically undetectable. Had to use the clamp/ bench/ severe force routine again in order to return the chassis to its original shape. It was the radical bending and force required to "get in and out" that made me leary about this fix. Bad design for servicing. Schematics readily available on the net. Thanks for your reply's!!! Sorry about no photos.

[g1]

It's not the design, it can be done without bending the chassis. No design requires that. You should be able to completely disassemble and remove all boards without chassis bending.
I can guarantee that the chassis was bent at the factory before the boards were installed, not after.

[Enzo]

Sometimes you must remove some other board first to make clearance room for the one you want. g-one is right, you never have to bend a chassis to get a board in or out.

[bassliner]

I could see no way to remove the board without the force bending of the chassis. The profile of the steel chassis does kind of a wrap around the circuit board. One edge of the circuit board is limited in movement because the pot stems protruded through the hole in the chassis. The opposite side of the circuit board with the power transistors lined up was partially enveloped and trapped by the steel chassis. I agree 100% it should not require such effort to remove and reinstall a circuit bd for service. A photo would help my case here here.
This may be a moot point since the repair is complete and successful despite the extreme and unexpected effort needed. I do appreciate everyones replys and advice...

[Enzo]

If I had one I could show you, but trust me, even if you can't see it, there is no way the chassis needs to be bent. If you can get the board back enough for the pot shafts to clear, but it now won't fit out the top, try sliding it out the end.

[bassliner]

Enzo, you may very well be correct. Maybe I overlooked something. Anyway it ended well!