Transformer part ID please

Tony Duell ard.p850ug1 at
Sun Jan 22 14:10:40 CST 2017

> Result! Whilst photographing the board to trace out that circuit (it's
> quicker for me than drawing it) I removed all the big capacitors. While they
> were out of circuit I tested them and discovered that not only was one dead
> in the -12V rail but also the through hole plating for another on the +12V
> rail had failed to a trace on the back of the board so neither the unknown
> 8-pin DIP or the LF351N were getting +12V.


> Fixed that and replaced the failed cap and now have -24V where it should be.
> If it helps with identification the unknown chip appears to be:
> 1 - GND
> 2 - 56k resistor to pin 3
> 3 - Gate of IRF523
> 4 - +12V via 10k resistor
> 5 - GND via decoupling cap
> 6 - connected to 2
> 7 - NC
> 8 - +12V
> That looks like an opamp to me, with bias pins connected to GND?

Does it? It looks like a 555 timer to me at first glance. I would have
expected another
capacitor from pins 2/6 to ground though.

1 Ground
2 Trigger (linked to threshold, and to output via a timing resistor)
3 Output (driving the MOSFET)
4 Reset/ (pulled high via a resistor)
5 Control Voltage (decoupled to ground)
6 Threshold (see 2)
7 Discharge (not used here)
8 Vcc


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