The controls for picture width and pincushion do nothing from 0-100%. This happened when a defective switch in a power strip power cycled the monitor 5 or 6 times in a row rapidly. Does anyone have a schematic or suggestions? Thanks, Joel

Hi if this is The Tatung chassis version of the D5259A then check the double diode in a single package near the HOT.

The reference maybe D434 the lower diode in the circuit will likely be S/C.

Rich B

The D434 double diode seems fine in circuit - around .44V drop across each diode and nothing the other direction. Any other ideas? Thanks, Joel

If its a DMV32 or DMV56 type dual diode package, or other high speed switch type, then you cant go by voltage drop. The switch time can degrade , and not be in spec.

It's a DMV32 and none of my normal sources seem to list it. Any ideas on where to get one? Thanks, Joel

Hi remove Q470 if it goes narrow then the diode is OK and the fault is in the control circuit if it stays wide then the diode is most likely but check C435 and C471.

Because you describe the failure mode it is most likely a component short rather than a capacitor value gone low.

Rich B

Thanks for the info Richard. I won't be able to work on this until later - possibly Monday. I'll let you know what I find. Thanks for the super help! Joel

Here's what I found -
Removed Q470 - no change
C471 measures 2.2uf & less than .4 ESR
C435 measures 7.76nf & infinity ESR - I don't think my meter is capable of measuring this cap?
Do you show what value C435 should be?
Removed C435 screen slightly ~.5" wider
Replaced C435 with more capacitance and screen also slightly wider
Reduced Capacitance and screen slightly wider
It seems that any change to C435 makes the screen wider
The control for width does nothing in any of these configurations - Remember also that pincushion does nothing either. Thanks for all the help, Joel

Hi you should not run this with C435 removed so maybe your diode is now blown,

C435 controls the % of flyback voltage across D434 lower diode, C434 I have as 1n6 & C435 as 7n5 but these depend on the scan coil and FBT, C434 & C435 are polypropylene caps and will have excellent ESR.

If you have an ultra fast 400V 3A diode better than 50nS trr then you could remove the leg to gnd of D434 and fit a diode from gnd to the junction of C435 & C434 with the band away from gnd i.e. pointing away from gnd on the circuit leave Q470 out.

Rich

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