ADI 931G monitor help needed.

[Ken]

Can anyone help?

I'm in the process of repairing an ADI 931G monitor but I can't find a
schematic anywhere. Basically (so far) I have discovered Q807
(BU2527AF) blown. Q831 (BU2520AF) blown and R866 (0.18 Ohm) safety
resistor open circuit.

Replacing the above results in Q831 blowing immediately but if I limit
the current through R866 by replacing it with a 100W household light
bulb the monitor fires up and settles with Q831 collector at approx
60V (this picture's not too good though!). Without limiting the
current Q831 sees 200V. Anyone seen similar problems before or have
any idea where I can get a schematics? - the only voltage reference
point I can see on the whole board is for a 75V rail which is
currently running at ~75.5V..

Any help is much appreciated.

thanks

Ken

 

[John Gill]

Have you checked the flyback ? My flyback test is as follows:
1. Measure the resistance from the HV anode to ground. It should
read open circuit. Any resistance ususally means it is bad.
2. Check the capactance from anode to ground. It should read about 2.5
to 3 nano-farads. I usually assume 1.5 to 5 is OK.
3. Check the primary winding with a flyback ring tester.
Note: these tests will not always find a bad flyback.
I also check the following:
4. I check any electrolytic capactors near the horizontal driver transformer.
5. Check for any shorted FET's or bad electrolytic capacitors in the
circuit that supplies the B+ voltage to the flyback (and HOT).
Hope this helps...
John



kenhunt@btinternet.com (Ken) wrote in message news:<51501f.0311111446.2979e52d@posting.google.com>...

Can anyone help?

I'm in the process of repairing an ADI 931G monitor but I can't find a
schematic anywhere. Basically (so far) I have discovered Q807
(BU2527AF) blown. Q831 (BU2520AF) blown and R866 (0.18 Ohm) safety
resistor open circuit.

Replacing the above results in Q831 blowing immediately but if I limit
the current through R866 by replacing it with a 100W household light
bulb the monitor fires up and settles with Q831 collector at approx
60V (this picture's not too good though!). Without limiting the
current Q831 sees 200V. Anyone seen similar problems before or have
any idea where I can get a schematics? - the only voltage reference
point I can see on the whole board is for a 75V rail which is
currently running at ~75.5V..

Any help is much appreciated.

thanks

Ken

 

[Ken]

jdgill@juno.com (John Gill) wrote in message news:<71016e83.0311120737.3f41ab2f@posting.google.com>...

Have you checked the flyback ? My flyback test is as follows:
1. Measure the resistance from the HV anode to ground. It should
read open circuit. Any resistance ususally means it is bad.
2. Check the capactance from anode to ground. It should read about 2.5
to 3 nano-farads. I usually assume 1.5 to 5 is OK.
3. Check the primary winding with a flyback ring tester.
Note: these tests will not always find a bad flyback.
I also check the following:
4. I check any electrolytic capactors near the horizontal driver transformer.
5. Check for any shorted FET's or bad electrolytic capacitors in the
circuit that supplies the B+ voltage to the flyback (and HOT).
Hope this helps...
John



kenhunt@btinternet.com (Ken) wrote in message news:<51501f.0311111446.2979e52d@posting.google.com>...
Can anyone help?

I'm in the process of repairing an ADI 931G monitor but I can't find a
schematic anywhere. Basically (so far) I have discovered Q807
(BU2527AF) blown. Q831 (BU2520AF) blown and R866 (0.18 Ohm) safety
resistor open circuit.

Replacing the above results in Q831 blowing immediately but if I limit
the current through R866 by replacing it with a 100W household light
bulb the monitor fires up and settles with Q831 collector at approx
60V (this picture's not too good though!). Without limiting the
current Q831 sees 200V. Anyone seen similar problems before or have
any idea where I can get a schematics? - the only voltage reference
point I can see on the whole board is for a 75V rail which is
currently running at ~75.5V..

Any help is much appreciated.

thanks

Ken

Thanks John. I'll give this a try. Hopefully the schematics are on
their way to me as well.

Ken