need help ident 2 transistor.

[ErwinsCat]

this is probably very easy for most people here, I'm trying to fix a multimeter protection clamp circuit, there was 2 transistor shorted and I changed them with a couple of generic NPN from a cheap eBay kit and it fixed the issue. now looking for a proper replacement as I'm guessing the cheap one probably not going to protect the circuit when needed coz of speed and other parameters. I'm having trouble finding info on transistor stamped 8050 6m c  the other one is stamped A992 FA5BC
I believe the first part is 2SA992 not sure about second part (FA5BC)
any help appreciated
thanks



KA_WHO

[Ian.M]

2SA992 - PNP, High h_FE and relatively high voltage but not that exotic compared to some Zetex 'superbeta' parts. May be difficult/expensive to source genuine parts.  Try KSA992 @ Mouser, which should be equivalent.

SS8050 - a little bit special because its high current for a TO92 package with relatively high h_FE as high currents, but nowadays as common as dirt.

Don't sweat the batch/lot codes. They are often totally undecipherable without the original manufacturer's production records.  *SOME* manufacturers encode a production line identifier and often a human readable date, but others just use alphabet soup as a key into their database.

However odds are your meter's clamping circuit doesn't use them anywhere near their full ratings.  e.g. if it clamps at low voltage, the voltage rating of the 2SA992 wont matter.  If you have *ANY* difficulty sourcing exact replacements from a reputable distributor, trace out the circuit and post it here for comment on how critical they are.

[ErwinsCat]

Hi, thanks for the reply, as you said it's probably not a critical component as it working with the generic replacement for a year now and haven't had any issues with it yet. I thought its better if I could replace them with proper parts. one issue I have with SS8050 replacement is the pinout is different from the stamped original device and that made me question if it's the correct part. I try to see if I can draw the schematic from the board but as far as I remember these 2 tranis are both used as diodes i think? i remember 2 pins were shorted together and I remember its remind me of those standard transistor/diode clamping circuit usually used in multimeters input.
Thanks

[Ian.M]

The various manufacturers '8050' pinouts are all over the place.  Maybe it was originally BTN8050A3, but it doesn't matter (as long as you can bend the leads to fit the footprint without shorting) as its equivalent to SS8050.

If they are diode connected, its even less likely that the specific gain and voltage ratings are critical.