Re: 7854 Repair & Restoration


Ed Breya
 

I looked at that vertical amp board again and found that the cans are plugged into Berg sockets, and there is thermal grease underneath for better cooling. Also, I hadn't noticed before that two of the pins on the bigger output amplifier are much longer, and were passed though unplated, un-socketed holes, for connection to the deflection plates. There's no solder on them either, and I can't remember if I clipped them off from other leads (very unlikely), or if they were plugged into loose Berg sockets attached to the CRT lead wiring.

If the 7854 hookup is made that way, that's another possible location for intermittent connections.

I also found another different board, which I had marked as from a 7904 (670-1630-04), so the first one must have been from a 7844. The 7904 board has the same arrangement of a TO-8 driver in Berg sockets, with the plastic clamp, but the output amplifier is a stud-mount case instead, mounted to a small aluminum heatsink bracket under the board. Likewise, the pins are in Berg sockets, except for the output ones, which are soldered to small wire jumpers that went to the CRT.

Ed

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