Help with finding Zener Diode Part# UZ-22BSC (Arcade Monitor)

[WolfgangFox]

Hello all,

I am repairing an arcade monitor (Tovis 1901CN/Happ Vision Pro MTG-XX01/WG K7300).  I need assistance with finding the Zener Diode Part #: UZ-22BSC listed in the parts catalog.

I don't quite understand how zener diodes are labeled.  UZ-22BSC comes up with nothing when doing an internet search, but 22bsc comes up with datasheets, and on the part itself is listed: 2(Z),2,2(3),C,p.  The first marking could be 2 or Z, and the 3rd marking could be 2 or 3.  These suckers are small even under a microscope.

I hope this is the right forum for this.  Thank you!

[BrokenYugo]

I'd bet on "22BSC", especially if you're sure the parts list matches the board revision, 21.22-22.09V@5mA is the critical data.

https://html.alldatasheet.com/html-pdf/281900/SEMTECH_ELEC/22BSC/3466/4/22BSC.html

If you have a schematic handy that would help to confirm.

[WolfgangFox]

Yes I do!

Please see attached, right in the center.

It does look like that.  Where would I find such a part?  I am so used to 1N or NTE equivalent part numbers. 

[wraper]

Just use any other 500mW zener with appropriate voltage rating.

[floobydust]

Uh, the * and 1% by the component values leads me to believe it's part of the X-ray protect circuit?

[fzabkar]

I see that the zener is a critical part of the HV shutdown circuit.

https://www.arcade-museum.com/manuals-monitors/Vision_Pro_(MTG-XX01_Series_13in_and_19in_CGA).pdf

AFAICT, the current through the zener is 2mA at the very most (C343 = 50V 4.7uF).

[floobydust]

It's a select +/-1% grade part which is not really available. Zeners are typically +/-5% or +/-2% and their datasheet test current varies.
22BSC spec V_Z=21.22-22.09V @ I_ZT 5mA. Close enough: BZX55B22 V_Z=21.55-22-22.45V @ I_ZT 5mA.

I think that zener is not likely to fail, it's in a low stress circuit but the electrolytic capacitors C343 or C379 I would suspect, if the X-ray prot is false triggering.

[WolfgangFox]

Uh, the * and 1% by the component values leads me to believe it's part of the X-ray protect circuit?

Yes.  The monitor is going into HV shutdown when power and signal is applied.  I just bought it secondhand from a guy local to me.  Part of the troubleshooting is disabling the diode (lifting one side) and seeing if you get a picture, then you know the HV circuit is bad.  Well, I just wanted to lift a leg of it to test it, because I think the original owner never did.  And when I was removing it, it broke.  So...  I need to replace it now, there is not enough on the legs of it to solder a wire or anything.

However I'm so used to the 1N part numbers, or NTE part #s, I was at a loss looking for a substitute or replacement.  Yeah, it rarely fails, I'm the one that "made" it fail by breaking it.  LOL

If you guys really want to take a look at it, here is a link to the manual / schematics:  https://www.arcade-museum.com/manuals-monitors/Vision_Pro_%28MTG-XX01_Series_13in_and_19in_CGA%29.pdf

Now, so just that I understand.  Grab a Zener Diode with a 500mW / 22v / 1% rating, and probably 2% would be ok?  So this one:  https://www.sicstock.com/products/mtzjt-7722b-7722-mtzjt-7722?variant=18350664253497&currency=USD&utm_medium=product_sync&utm_source=google&utm_content=sag_organic&utm_campaign=sag_organic&com_cvv=8fb3d522dc163aeadb66e08cd7450cbbdddc64c6cf2e8891f6d48747c6d56d2c  would be ok?

-Pat
-Pat

[floobydust]

1N5251B is V_Z=20.9-23V @ I_ZT 5.6mA, pretty wide spread so I didn't recommend it.
MTZJT-7722B V_Z=20.64-21.71V @ I_ZT 5mA. On the low end of the original part.

[Wallace Gasiewicz]

You could test a zener (once you get it) by using a variable power supply and a voltmeter. If you have a variable voltage variable current PS, you could hook it up to the Zener and see what voltage it really is.If you set the current very low and just increase the volts the volts will stop at the real zener value. 
So if you can order maybe ten or more  of the same zener in your range, you could test them and probably find one that is real close to your value. I take it the value is supposed to be 22 volts....

[TimFox]

The Zener datasheet from Semtech cited above  https://html.alldatasheet.com/html-pdf/281900/SEMTECH_ELEC/22BSC/3466/4/22BSC.html  for the 22BS series shows 5 voltage-tolerance options for the Zener voltage at 5 mA:
20.23 to 22.61 V for the 22BS, or 21.42 V +/- 5.6%
 ...
21.22 to 22.09 V for 22BSC, 21.66 V +/- 2%
21.68 to 22.61 V for 22BSD, 22.15 V +/- 4.5%
The sorting bins actually are somewhat disjoint.

[wraper]

Uh, the * and 1% by the component values leads me to believe it's part of the X-ray protect circuit?

Op said it's an arcade monitor. Hand picking 1% zener for that is nonsensical, not to say 1% from what value? From what OP said I doubt that circuit is from the monitor, just something else he found on internet.

Please see attached, right in the center.

It does look like that.  Where would I find such a part?

[floobydust]

Back in the day, regulatory was a bit crazy about X-ray protection and the critical parts were precision to avoid a calibration on beam current.