RCA RPTV CTC169PT wont't power up

[JoeNeZZ]

I have a ctc169pt chassis that won't power up
this unit has been worked on before as it appears that the H out
transistor & the PS IC have either been replaced or resoldered.

H out transistor appears to be ok (not shorted or open) in circuit,
however there is no voltage present at E C or B in stand by mode.

I checked a the diodes coming off the mains, they test ok out of
circuit, I replaced CR4118 even though it tested ok.

still no standby voltage.
I checked the big stand up power resister that comes off the mains (1.8
ohm 15 W) & it was open
I replaced the the resistor, applied power & measured for voltage & no
difference,
I checked the resister again & found the new one was now open, no
spark,smoke or heat,
it just quietly opened.

I have no experience with this chassis or any schematics for it.

does anyone have any ideas what the problem might be ?

Thanks in advance, Roger

 

[Chuck]

I have a ctc169pt chassis that won't power up
this unit has been worked on before as it appears that the H out
transistor & the PS IC have either been replaced or resoldered.

H out transistor appears to be ok (not shorted or open) in circuit,
however there is no voltage present at E C or B in stand by mode.

I checked a the diodes coming off the mains, they test ok out of
circuit, I replaced CR4118 even though it tested ok.

still no standby voltage.
I checked the big stand up power resister that comes off the mains (1.8
ohm 15 W) & it was open
I replaced the the resistor, applied power & measured for voltage & no
difference,
I checked the resister again & found the new one was now open, no
spark,smoke or heat,
it just quietly opened.

I have no experience with this chassis or any schematics for it.

does anyone have any ideas what the problem might be ?

Thanks in advance, Roger

Shorted power supply diodes or switched regulator output transistor.
If the transistor is shorted, replace the drive ic and check the
electrolytic capacitors around it for high esr. Replace all that have
high esr. Chuck

 

[JoeNeZZ]

Q4101 tested ok
Q4401 tested ok
CR4122 tested ok
CR1 thru CR4 tested ok
Replaced:
C4101, C4102, C4104, C4106, U4101, CR4118, C2, C9, C7K
still blows 1.8 ohm power resistor when power is applied
any ideas on what to check next ?
Thanks' Roger

 

[JoeNeZZ]

I traced the problem to a shorted Q37F on the heat sink of the
deflection board
Does anyone have an RCA part number & or a cross for this part the
number on the part reads "R138" but my part supplier has no listing of
it nore does NTE so it is probably an RCA house number.

Thanks, Roger