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20" White Westinghouse...no power

G

George

Jan 1, 1970
0
20" White Westinghouse
TV Model WVT-61901
Year Jan 1999

Will not power up. Just stopped working one day. Brought down to
workshop, plugged it in and it worked. Back upstairs and wouldn't
work next morning. Now won't power up at all.

Checked bridge...ok. Found 5W 1.8K power resistor that reads 2.5K.
Is this normal for these large resistors to be off by so much? It
feeds a zener and capacitor circuit so i'm thinking it's part of some
low voltage circuit which might explain the problem ??

Don't have one handy and not close to town so wondering anyone's
thoughts on this.

thanks.
 
S

Sam Goldwasser

Jan 1, 1970
0
20" White Westinghouse
TV Model WVT-61901
Year Jan 1999

Will not power up. Just stopped working one day. Brought down to
workshop, plugged it in and it worked. Back upstairs and wouldn't
work next morning. Now won't power up at all.

Checked bridge...ok. Found 5W 1.8K power resistor that reads 2.5K.
Is this normal for these large resistors to be off by so much? It
feeds a zener and capacitor circuit so i'm thinking it's part of some
low voltage circuit which might explain the problem ??

Did you disconnect at least one end of the resistor? It might be open
and you're the resistance of other parts in the circuit.

Resistors shouldn't be that far off. However, I doubt the incorrect
resistance is the problem. Did you actually check that the resistor
is marked 1.8K? Often, the manufacturer will put in a part with a
different value than in the schematics or labeled on the PCB as a design
fix or improvement.

Assuming the resistor itself is marked 1.8K, then it's likely changed
value due to overheating or some other cause. Have you checked the
zener and any other parts it's feeding?

--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
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Important: Anything sent to the email address in the message header is ignored.
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G

George

Jan 1, 1970
0
Hi Sam...thanks for the response.
Did you disconnect at least one end of the resistor? It might be open
and you're the resistance of other parts in the circuit.

I completely yanked it and get this 2.5K reading. It is very clearly
labeled on the resistor as 1.8K Ohm 5W...it's a good sized ceramic
thing.
Assuming the resistor itself is marked 1.8K, then it's likely changed
value due to overheating or some other cause. Have you checked the
zener and any other parts it's feeding?

This power resistor is fed from a diode giving a half-wave rectified
120V voltage into one side of it...and on the other it connects into a
zener and then a a 680 ohm 1/4W resistor....those check out fine with
a reasonable resistance.

I think i'll source to try and source one of these 1.7K 5W
resistors...can't cost that much. Maybe it's dropping too much
voltage? I don't have a schematic or a part number for the zener to
really tell.

Any more ideas more than welcome...thanks!!
 
S

Sam Goldwasser

Jan 1, 1970
0
Hi Sam...thanks for the response.


I completely yanked it and get this 2.5K reading. It is very clearly
labeled on the resistor as 1.8K Ohm 5W...it's a good sized ceramic
thing.


This power resistor is fed from a diode giving a half-wave rectified
120V voltage into one side of it...and on the other it connects into a
zener and then a a 680 ohm 1/4W resistor....those check out fine with
a reasonable resistance.

I think i'll source to try and source one of these 1.7K 5W
resistors...can't cost that much. Maybe it's dropping too much
voltage? I don't have a schematic or a part number for the zener to
really tell.

It's certainly worth trying, easy and cheap enough.

What else is it feeding?

--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
+Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
| Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

Note: These links are hopefully temporary until we can sort out the excessive
traffic on Repairfaq.org.

Important: Anything sent to the email address in the message header is ignored.
To contact me, please use the feedback form on the S.E.R FAQ Web sites.
 
D

dkuhajda

Jan 1, 1970
0
20% tolerance power resistor. Could have been as high as 2.2K ohm. Was
the meter properly calibrated recently? If not, the assumption about it
being 2.5K could be wrong.

That tv is a Daewoo made elcheapo. The 2K resistor is a dropping resistor
for the standby power source circuitry. If the proper voltage is measured
on the zener diode with the tv safely plugged into an isolation transformer
for disassembled testing, there is no problem in that part of the circuit.

A bit more standard tv set troubleshooting is in order to narrow down the
problem.

David
 
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