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honeywell st9103a fan timer board


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honeywell central AC/heat Electronic fan timer st9103a 1036. Honeywell is no help. They want me to buy a new board for 150$. I believe its the IC (opto-sensor) on the board that's bad. I have not been able to find a schematic of this board. The IC is labeled:

L 9948


(large dot) Y

I've tried a few on line part suppliers and they cant identify it. It has four pins.

Home was hit by lightning and it fried 3 items on 3 different house circuits One was the AC. The above board is telling the fan to turn on, even though the thermostat is off. I've troubleshooted and believe its this IC and want to replace it.

Can anyone help me finding the original manufacturer or a generic replacement?

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If I understand correctly what you are referring to, I've no recollection of ever seeing either an internal wiring or internal schematic diagram for these boards. There are block diagrams and connection diagrams available from the manufacturers and from some board venders but they don't contain any information on the internal circuitry that would aid you in completing a component level diagnosis.


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Is there an electronics store in your area? Not a chain store like Best Buy, a Mom & Pop shop that does their own repairs. I have some vintage audio equipment that I've had fixed for cheap. My '60s Sansui amp had a handful of bad caps and a burnt transistor replaced, the myriad of switches cleaned, and it got scoped so I had the output ratings for around $50. They should be able to figure out what broke and get you parts.

For you audiophiles out there: the amp is only 55 watts per side at 8 ohms, but with 3dB of headroom it absolutely screams. I wish I could remember the model.


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