Help identify component

[redwire]

Re: Help identify component

2N2646 pinout seems to be an oddball metal can, non-standard TO-18 case. TO-18 (UJT) so the tab is at a weird angle compared to the typical transistor TO-18 configuration. Note they use bottom view for pinouts on datasheets.

A 2N4871 or 2N4851 might also work. UJT's in a metal can are long obsolete.
Tenatronics Ltd. 50-114, Motomaster 11-1519, Sears 12V 10A Automatic Battery Charger

[Willybb]

Re: Help identify component

Hi redwire

Thanks for getting back to me. I thought I was loosing my mined as everything I looked up had a different tab position. I finely found the attached picture below which corresponds with the 2N2646 I have. Wanted to verify with someone else to make sure this pin layout was correct before I let the smoke out. I only have a couple of these to play with. I'll get it soldered in and see if this is the fix.

Why is this component labeled Emitter/Base1/Base2 when most every other transistor is Emitter/Base/Collector?

Thanks again for the help.
Cheers
Willy

[redwire]

Re: Help identify component

OK your datasheet pic is showing a transistor style TO-18 pinout I've seen many different pinouts for the 2N2646 on the Web.
You can ID the emitter as (+) on multimeter diode-test and readings to both bases. Some TO-18 cans have the substrate (lead) emitter connected to the can, others have all three leads isolated. I'm not sure why the part labels are so weird, with no collector and two bases.

The battery charger circuit can't damage the part if you put it in wrong (emitter correct but bases flipped) and the trimpot is not dialed to the max.
Or maybe build an UJT oscillator or LED blinky to verify it works.

I updated the previous schematic, can you check it with what you have got or post pics.

[budm]

Re: Help identify component

UJT:
https://www.elprocus.com/introductio...and-operation/

https://www.watelectronics.com/uni-j...working-types/

[Willybb]

Re: Help identify component

I updated the previous schematic, can you check it with what you have got or post pics.

As far as I can tell the only difference from your schematic to my PCB is the addition of a 6.8K resister (measures 6.9K) across the 5K potentiometer. I had removed the pot and one end of all resisters to check their values.

I'm planning to solder in the 2N2646 and test the Charger tonight. Lets hope for no smoke. :-)

Willy

[Willybb]

Re: Help identify component

Hi Guys

The good thing is there was no smoke. The bad thing is there was no output. So either the replacement 2N2646 I got was defective or that wasn't the problem? I need to get into this thing a little deeper.

I notice that the 8.2 zener looks strange. Almost like it has been hot? I need to test it or maybe just replace it.

So the adventure continues.

Willy

[redwire]

Re: Help identify component

It won't start charging unless a battery is present.
The SCR's will stay off until the UJT starts oscillating and driving the trigger transformer- which needs power downstream of the SCR's.

You could try, with it unplugged, using a lab power supply or something to give it 12VDC at the charger's output terminals. You should see ~8.2V across the zener and the UJT will oscillate assuming the trimpot is set for it to shut off at 14V or so.