Diamond Monitor 1997 (ACER 7279G) Help

V

Verdons

Guest
I am attempting to fix this 19" monitor. I have found a schematic on a
Russian site :) part of the eht section is scanned and viewable here
http://users.tpg.com.au/users/verdons2/7279.htm

Symptom: no EHT /green light on.
I have disconnected the smps from main board and it runs ok.
I have checked caps around Hor out and they look ok with regards to ESR.
I can find no bad joints around the FBT or HOT drive Txfmr.
I checked the FBT and it rings well, the 3000p cap on the eht lead measures
ok.
I pulled out the Q313 HOT BU2520DX and replaced it with a BU508D (had on
hand) and also Q304 an IRF640 (was 634) and tried a 740 (on hand).
Also I replaced the diode D305 and the 4 470p/2kV caps across the HOT's C-E.
I got a picture for about 5 secs, there was a short blink and then back to
nogo status
When in this condition and I power on:
the HORV signal from IC304 tda4855 driving this circuit appears for a few
seconds then stops.
There is a signal on the BU2520 base before HORV stops.
I can see a switching signal on Q304's gate.
45V on HOT emitter
There is a slight fizzing sound...perhaps heating of the FBT primary?

Should I replace the HOT and Mosfet with the correct type and see what
happens?
Is there some other component I should check before I do this?

Thanks in advance
Russell (wish I had a variac!)
 
I must go by your description. I have not worked on the model you have. I
am sure, you need the correct HOT for sure. The flyback most likely has to
also be replaced. I have seen this before, but not in the make of monitor
you have.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
=========================================


"Verdons" <spamverdons@tpgi.com.au> wrote in message
news:3fc08c8f$1@dnews.tpgi.com.au...
I am attempting to fix this 19" monitor. I have found a schematic on a
Russian site :) part of the eht section is scanned and viewable here
http://users.tpg.com.au/users/verdons2/7279.htm

Symptom: no EHT /green light on.
I have disconnected the smps from main board and it runs ok.
I have checked caps around Hor out and they look ok with regards to ESR.
I can find no bad joints around the FBT or HOT drive Txfmr.
I checked the FBT and it rings well, the 3000p cap on the eht lead measures
ok.
I pulled out the Q313 HOT BU2520DX and replaced it with a BU508D (had on
hand) and also Q304 an IRF640 (was 634) and tried a 740 (on hand).
Also I replaced the diode D305 and the 4 470p/2kV caps across the HOT's C-E.
I got a picture for about 5 secs, there was a short blink and then back to
nogo status
When in this condition and I power on:
the HORV signal from IC304 tda4855 driving this circuit appears for a few
seconds then stops.
There is a signal on the BU2520 base before HORV stops.
I can see a switching signal on Q304's gate.
45V on HOT emitter
There is a slight fizzing sound...perhaps heating of the FBT primary?

Should I replace the HOT and Mosfet with the correct type and see what
happens?
Is there some other component I should check before I do this?

Thanks in advance
Russell (wish I had a variac!)
 
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