Pentranic Model 1125 / CH-288 High Voltage Shutdown problem

[vf1100c]

I have a 25" Pentranic monitor that powers up and makes a ticking sound. It sounds like a relay clicking on and off. I assume that it is in High Voltage Shutdown mode. The chassis had a broken POT on the adjustment board, VR4 H-HOLD. I have replaced the POT, but the chassis still does not power up.

I have removed the HOT, which includes the extra protection diode, and it appears to function properly with my DMM set to diode check. I have also ohmed out the yoke, with resistances of 2 ohms and 5.8 ohms. Are these the proper DC readings for this chassis?

I have also been working with a schematic labeled "Model 1127, 1527, 1532 -> CH-288 CGA". It seems that my flyback (marked MHF023-45) does not match the schematic. According to the schematic, Pins 1,2,9,10, and 11 should have continuity as should Pins 3,4,5,7,and 8. I removed my flyback and it measures continuity on Pins 1,9,10, and 12, as well as Pins 2,3,4,5, and 8. Does this mean that my flyback is bad, as Pin 2 is on the other winding? Or is my schematic wrong for this model?

Any advice on getting this chassis out of shutdown mode would be appreciated.

[grantspain]

is the hdt(hot) a bu2525af?

[vf1100c]

I will have to double check when I get home, but I think that it was a BU2520DF.

[Rickn]

Hi Chris, take out the HOT, then connect a normal light bulb, say 60 watts in series with the collector foil pattern and ground.

Now the bulb is the load instead of the HOT

Now fire it up.

Does the bulb light, if so check the B+ at Cathode D901, somewhere around 115VDC is normal.

If you have all this then we have a problem in the horizontal circuit.

Let me know how this fairs and we can try a few more things.


Good Luck

Rick Nieman
Rick@Niemandispays.com
www.Niemandisplays.com