Power supplies in TVs, VCRs, etc

[ljcox]

I attampted to attach the photos of the relevant section but they were too big.
Does anyone know how to zip jpeg photos in Windows XT?

Len

 

[ljcox]

Here are 2 photos of the relevant part of the Circuit.

I presume that the starting string is the 5 resistors of 220k. I measured them in circuit and all are correct.

I replaced CP011, CP025, CP031, CP032 & CP040 as they all had high ESR, but to no avail.

The only issue found so far is that RP028 and RP030 are 15 Ohm when I measured them in circuit with an Ohmmeter. So one or both must be high.

Any suggestions appreciated.

Len

 

[Nigel Goodwin]

Here are 2 photos of the relevant part of the Circuit.

I presume that the starting string is the 5 resistors of 220k. I measured them in circuit and all are correct.

I replaced CP011, CP025, CP031, CP032 & CP040 as they all had high ESR, but to no avail.

The only issue found so far is that RP028 and RP030 are 15 ohm when I measured them in circuit with an Ohmmeter. So one or both must be high.

Checking them in circuit will tend to give strange reading, particularly with a digital meter, disconnect one end of each resistor to test them.

You also might try testing the 4.7 ohm in the source of the FET, this provides current monitoring, if it's slightly high the supply high trip off.

 

[ljcox]

Here are 2 photos of the relevant part of the Circuit.

I presume that the starting string is the 5 resistors of 220k. I measured them in circuit and all are correct.

I replaced CP011, CP025, CP031, CP032 & CP040 as they all had high ESR, but to no avail.

The only issue found so far is that RP028 and RP030 are 15 <a href="#">ohm</a> when I measured them in circuit with an Ohmmeter. So one or both must be high.

Checking them in circuit will tend to give strange reading, particularly with a digital meter, disconnect one end of each resistor to test them.

You also might try testing the 4.7 Ohm in the source of the FET, this provides current monitoring, if it's slightly high the supply high trip off.

Thanks Nigel,
I put a short across the ends of the 220k resistor string (they are surface mounted resistors) to measure them.
This eliminated the vaguries due to the supply impedance. Across each resistor I measured about 176k which is correct (220k // 880k). (4 resistors in series across one)

To measure RP028 and RP030, I oriented the meter so the CB junction of TP022 would be reverse biassed.

So I feel the resistance readings are correct.

I think I did check the 4R7 so I'll re-check it.

Len

 

[ljcox]

Edmond,
Here are the photos you requested in the PM.

Thanks for the help.

Len

 

[positive logic]

in tv, the faults maybe in regulator or horizontal output transistor. there are also faults that the over current protection and over voltage protection kick-on.
If horizontal output transistor is good the fault maybe in regulator circuit which drive the switching transformer.
in feedbak circuit, try to check the opto-isolator/relay.