ID Fuse: SG5A

[Keno48]

Repairing GE Washing Machine Control Board (PCB). Have a blown power protection front-end to a low voltage section: Crowbar configuration of Varistor immediately after the fuse. Both the Varistor & fuse are blown. Can't locate any WEB info on the fuse using its markings: 'SG5A'. This is a miniature (~0.25"long X ~0.1"dia), grey axial lead fuse on a PCB with a label of 'F2' on the PCB. Appearance is that of a 1/8W resistor in shape, grey in color with the markings 'SG5A' and labeled as 'F2' on the PCB. Multimeter measurements indicate open fuse (Inf Resistance). Have confidence that the device is at the front end by ringing out the 110vAC power wiring to the components. Machine uses various ICs and low power relays, so lo voltage DC is created on the board (must be subsequent to this front end).

 

[Tony Stewart]

What is your grid tolerance? Ours is 120V +/-10% Size according to your region.
For here I might choose 140Vrms tolerance converted to peak voltage.
https://www.digikey.ca/en/products/detail/epcos-tdk-electronics/B72210S2141K101/593828

SG5A is 5A in a non-std size.

 

[Keno48]

Thanks Tony,
I was not clear in my post - I have the MOV part number & it is ordered. What I need is the info on the fuse, viz, fast-acting, super-fast acting as, for example, a semiconductor fuse, or slow-acting. I did suspect that the 5A was amps, but this circuit ONLY supplies the ICs (discrete logic chips & likely a uP), all of the motors(agitator & water pump) and mode-shifter are directly AC(2-spd agitator) powered and controlled via lo-voltage relays. 5A seems like overkill for the current draw(excluding the motors) of the logic board & relays alone, but I do not have experience with these crowbar configs. Does a crowbar front end have an unusually large fuse? There is another fuse immediately after the MOV, also protecting the PCB. Could the 1st fuse be used exclusively for the crowbar action via the MOV & the 2nd fuse for protection of downstream current draw from the lo-amp PCB? If the 1st fuse is exclusively for the MOV are these typically very fast or slow acting?
Would a schematic of the front end of the supply help? I did reverse-engineer (from the PCB traces) the initial section of the power supply.

BTW, a lost leg of the 120v-AC supply to the house destroyed the components. The service tech repaired the line break and informed that they have a +/-5% tolerance on the AC voltage. What likely burned the parts was quasi-continual intermittent make-break connections as the wire failed to the house. The machine was not operating at the time, but obviously, the control board is continuously powered.

Again, many thanks for your rapid reply

 

[Tony Stewart]

Given that the MOV was destroyed by the transient grid connection, I'd say it iswas a slow blow. A Fast blow might have done better.

Time to retrofit a fast-blow ? https://hcess.ca/product/ssq-5-5a-smd-fuse-fast-blow/

 

[Nigel Goodwin]

Given that the MOV was destroyed by the transient grid connection, I'd say it iswas a slow blow. A Fast blow might have done better.

Time to retrofit a fast-blow ? https://hcess.ca/product/ssq-5-5a-smd-fuse-fast-blow/

If it was a slow-blow, then there's a good reason for it - it shouldn't be replaced with a 'fast'-blow one - a fast-blow one will most likely intermittently blow for no reason.

 

[wkt_1]

If it's a slow-blow fuse, there's a valid reason for its specification. Replacing it with a fast-blow fuse could result in intermittent and unnecessary blowing.

 

[Tony Stewart]

In your case, abnormal conditions caused the MOV to fail which normally can withstand 100A as if no fuse was in the circuit. So the race to fail was a tie. But at least it protected the rest of the circuit, we hope, but one cannot say for sure.

I think a 0.25" L fuse must be for low voltage. (?)

One way to reduce doubt is to order both FB and SB fuses and when the FB fails replace it with the SB.
Or to test the rest of the PCB try with the SB 1st then the FB and if that fails, revert to SB. A FB fuse might fail again if there are secondary shorted parts. If the FB fails you know the rest of the board also has a failed component but pretesting with a DMM might give some clues.

Ceramic bodies are used for both types. Some are leaded for THT use on PCB then may have an insulator sleeve used over top.

Either way control boards are often ridiculously overpriced and worth repairing.

very diverse catalog

https://www.diverseelectronics.com/upload/catalogues/CONQUER-Catalogue-2023.pdf

A PTC is an alternate possible solution.

Nothing will protect against a lightning-induced primary voltage failure.