Need some advice...21inch monitor.

[Kees]

KDS VS-21E, FCC-ID evokd-2100k

HOT Q415 short, after replacement it blows again.
When i feed the horizontal stage from an external power supply picture is
ok.
Checked internal supply with a light bulb. Looks ok. Voltage is approx. 35
volts.

Please help,
Thanks
Arold

 

[James Sweet]

KDS VS-21E, FCC-ID evokd-2100k

HOT Q415 short, after replacement it blows again.
When i feed the horizontal stage from an external power supply picture is
ok.
Checked internal supply with a light bulb. Looks ok. Voltage is approx. 35
volts.

Please help,
Thanks
Arold

35v? Shouldn't it be more like 90-180v?

 

[Kees]

This monitor has a separate HOT for the high tension part and one for the
horizontal deflection.
The supply voltage for the HT part is approx. 200V. The HT is working fine.

 

[John Gill]

"Kees"
Some monitors use a separate chopper circuit to provide the operating
voltage for the horizontal sweep. I would look for an FET transistor
on a heat sink near the horizontal sweep output transistor. Also check
the capacitor, zener didoe and any other parts in that circuit.
John

 

[Kees]

Hi John,

I already checked/replaced all parts in this chopper circuit.
(the chopper FET was gone as well, replaced by original part)
When I connect this circuit to a light bulb all looks ok.
Checked waveforms with an oscilloscope and as far as i can see this circuit
is working fine.

Kees