ctc203 B+ too high
 

CTC203J2 RCA Hospital Model #J20541

Intermittent 3 strikes symptom but "sometimes" starts up, turns on and
displays great pic and good sound but B+ seems to regulate about 10 - 15
volts too high.... about 154 vdc.
I found that if I reduce the B+ going to pin #2 of flyback by about 10 volts
with a 27 ohm resistor that it powers on just fine, every time, so I am
hoping that if I can reduce the regulated B+ to a lower correct voltage that
all will be OK and will work fine as it should without the voltage dropping
resistor.
I checked values of resistors and electrolytics ESR all around SMPS primary
(changed R14108, 0.1 ohm, 3W) and secondary without finding any significant
deviations from the norm. Resoldering around Flyback, HOT, L4401, HDr
xfmr, etc had been done and has been redone.

How do I reduce the B+ ..... adjust? component change?

TIA
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
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ctc203 B+ too high
 

On Thu, 12 Jan 2006 15:32:31 -0800, "sofie" wrote:

CTC203J2 RCA Hospital Model #J20541

Intermittent 3 strikes symptom but "sometimes" starts up, turns on and
displays great pic and good sound but B+ seems to regulate about 10 - 15
volts too high.... about 154 vdc.
I found that if I reduce the B+ going to pin #2 of flyback by about 10 volts
with a 27 ohm resistor that it powers on just fine, every time, so I am
hoping that if I can reduce the regulated B+ to a lower correct voltage that
all will be OK and will work fine as it should without the voltage dropping
resistor.
I checked values of resistors and electrolytics ESR all around SMPS primary
(changed R14108, 0.1 ohm, 3W) and secondary without finding any significant
deviations from the norm. Resoldering around Flyback, HOT, L4401, HDr
xfmr, etc had been done and has been redone.

How do I reduce the B+ ..... adjust? component change?

TIA

Sofie,

Check on secondary side, these SMPS use feedback regulation full time,
TL431 is the TO-92 size via 2 1% (green bodies) resistors and
regulates SMPS circuit via optisolator.

Like mine, I had one run high, was in that secondary side feedback
circuit.

ATC113 uses same SMPS, horizontal and vertical designs as CTC203.

Cheers, Wizard

ctc203 B+ too high
 

As I recall some of the early ctc203 SMPS had a goldenrod service
bulletin on the transformer pads lifting and the ultra small circuit
traces going open.

SMPS not regulating or regulating high, always check the feedback
circuit components.

ctc203 B+ too high
 

Wizard:
I am having a similar problem like the one that Sofie described.
I replaced both optos and the TL431 and still the B+ seems high..... it
appears to be regulating OK... I can vary in AC line input from 90 to
130 volts and the B+ stays within a few volts of 156, with or without
the flyback load. All other parts that I could identify in the
secondary feedback circuitry... diodes, electrolytics, etc test OK.

Did you find a faulty component or did you adjust slightly the balance
of R1 / R2 ?
How did you get the B+ lowered? ..... what is the correct B+ voltage?

David:
..... the solder joints and the circuit traces are in perfect condition,
but I resoldered them anyway and checked the traces with a meter and
with a magnafying glass.

Thanks for your inputs.
electricitym
..
..

ctc203 B+ too high
 

sofie wrote:

How do I reduce the B+ ..... adjust? component change?

TIA
--


Dan, make sure the flyback wasn't replaced with a generic one at some
point. Excessive hv is normal for this. I usually add a 472 2KV disc
across the timing cap to reduce the HV when a generic is used.

John