Diode identification for Mitsubishi(Digital) monitor

[MW]

I have a 21" monitor with a damaged power supply. I have everything
under control except there are two diodes I cannot identify and even
looked at Partminer and ICMaster.

The monitor is a Digital (aug '95) VRC21-HA FCC ID: A09-VRC21 rev E01
made by Mitsubishi.

Both diodes are open. Locations D905 and D904 in SMPS. Markings are
"KIV455" or possibly "K1V455" both 5's have a "-" over top.

Any idea what I can replace these regular looking diodes with? Are they
just ordinary diodes that I can use a similar sized diode in there
places?

They are inbetween two 680 uf 250 volt electrolyic caps I assume for
filtering since they are part of the SMPS.

Thanks for any help.

[Steve Bell]

On 16/11/00 8:00 pm, in article 3A143DBE...@sympatico.ca, "MW"
<mwa...@sympatico.ca> wrote:

These are high voltage zeners used for mains overvoltage protection. Sony
used something similar on the PSU's in the DEC VRT19-HA. I always replace
with a 150V MOV, these conduct at 200V DC. If your using on 220/230V check
the mains voltage auto switching circuitry before powering on again.

Steve Bell

[MW]

Thanks Steve.

I am surprised that they are zeners because they are marked on the cct board
as normal diodes. I will take your experience and replace them with the MOV's
you suggested.

[MW]

I ordered a couple of ECG MOV's to put in their place. I do wonder though;
MOV's are non-polarized and act as surge supressors. Zeners do not conduct in
reverse unless breakdown voltage occurs. Do MOV's absorb any overvoltage in
this circuit?
What size MOV (energy WTM (joules)) rating do you suggest? I did order a 150V
MOV with a bigger joule rating. I never had to order one before and when I
was asked by the clerk I told them the bigger joule rating. The order doesn't
go in until Monday so I still have time to change it.

Thanks

[MW]

[w_...@my-deja.com]

MOVs don't absorb anything. They simply become short circuits when
the voltage exceeds limits. They also degrade with use.

I recommend nothing because I don't understand what your circuit is
and what the diode purpose is. However you have great need of
application notes at General Semicondutor (www.gensemi.com?): topic
Transzorbs.

In article <3A156D30...@sympatico.ca>,

mwa...@sympatico.ca wrote:
> I ordered a couple of ECG MOV's to put in their place. I do
>wonder though; MOV's are non-polarized and act as surge
>supressors. Zeners do not conduct in reverse unless breakdown
>voltage occurs. Do MOV's absorb any overvoltage in this circuit?
>What size MOV (energy WTM (joules)) rating do you suggest? I did
>order a 150V MOV with a bigger joule rating. I never had to
>order one before and when I was asked by the clerk I told them
>the bigger joule rating. The order doesn't go in until Monday so
>I still have time to change it.

Sent via Deja.com http://www.deja.com/
Before you buy.

[MW]

I have to admit I felt rather paranoid about replacing the diode's with MOV's
even though I felt confident in your expertise. I did it after replacing any
bad caps and the other components that failed and its working great. The DC
voltage across each MOV is approx 150 volts with the monitor running on a 120
volt AC.

Thanks Steve.