Author Topic: Assistance identifying TO92 in GFCI outlet  (Read 515 times)

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Offline FliesLikeABrick

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Assistance identifying TO92 in GFCI outlet
« on: April 02, 2018, 03:38:27 am »
Hello all,

I have an older GFCI outlet which failed and has been replaced.  For fun/education I have disassembled it to discover the root cause of failure.  A TO92 has the side blown out of it, but I cannot identify this component.  My Google abilities are failing to find a datasheet or confirm what this is. 

It's a TO-92, so I suspect a transistor

The last line next to the Motorola logo is "741" which makes me ponder if it's an LM741 ... but I can't imagine that coming in a 3-pin package

Image attached and at https://photos.app.goo.gl/hpyCdNyq2hQXE97N2

The TO92 with the blue face.  Markings:
X289
63-1
(M)741
« Last Edit: April 02, 2018, 03:40:22 am by FliesLikeABrick »
 

Offline technogeeky

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Re: Assistance identifying TO92 in GFCI outlet
« Reply #1 on: April 02, 2018, 05:17:20 am »
I didn't find anything conclusive. My intuition says it must be an SCR or triac or thyristor or something of that nature.

I found this 1975 Motorola master selection guide. From the part designations, it would seem that "28963-1" could be a reference to a SCR (in the sense that the SCRs are the only parts with such long identifier, and hyphen in it).

Furthermore, while looking for that IC I found this patent which uses the RA9031 in its description. The only suitable part that could be a three pin device in this description is an SCR.
 

Online glarsson

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Re: Assistance identifying TO92 in GFCI outlet
« Reply #2 on: April 02, 2018, 05:27:03 am »
741 on TO92 is a date code. Week 41 of a year ending in 7 (..., 1987, 1997, 2007, 2017).
748 on DIL8 is a date code. Week 48 of a year ending in 7, probably same year as the TO92.
 

Offline amc184

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Re: Assistance identifying TO92 in GFCI outlet
« Reply #3 on: April 02, 2018, 08:46:22 am »
Maybe a BCX28?
 

Offline floobydust

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Re: Assistance identifying TO92 in GFCI outlet
« Reply #4 on: April 02, 2018, 02:20:54 pm »
GFI's use a small SCR to energize the circuit-breaker, like MCR100-6.
If the GFI circuit-breaker gets stuck, the SCR and coil stay energized and things burn up. Normally, the circuit-breaker trips and removes power from the GFI circuit.
But if this does not happen, the coil melts and open circuits, but here the SCR popped.

Because this has a safety function and GFCI's don't last forever, I would not repair it- I would bin it.

More info on the IC datasheets: LM1851, RV4145A, FAN4147 Ground Fault Interrupter
 

Offline FliesLikeABrick

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Re: Assistance identifying TO92 in GFCI outlet
« Reply #5 on: April 03, 2018, 02:33:10 am »
Because this has a safety function and GFCI's don't last forever, I would not repair it- I would bin it.

More info on the IC datasheets: LM1851, RV4145A, FAN4147 Ground Fault Interrupter

Thanks, agreed - I do not intend to repair it as much as to take these steps for their educational purpose.  I will look into SCRs and their role in this application.
 

Offline SeanB

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Re: Assistance identifying TO92 in GFCI outlet
« Reply #6 on: April 03, 2018, 04:01:20 am »
In this application you are looking for a sensitive gate SCR, as they require a lower trigger current to turn on, and the device is probably only a 200mA 400V rated device, with a gate requirement of 1V5 0.5mA to trigger it. Older units used a Gate Controlled Switch, which is a SCR with all 4 internal junctions brought out, and they typically were used with the anode gate triggering the trip relay instead of the cathode gate like almost all SCR units. They typically used a BRY39 GCS device to do the detection and triggering all in one package.
 
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