RCA Model F31632E1 (CTC 187 CK) Pincushion or power supply

[Ron Novini]

Have an unusual problem with an RCA Model F31632E1 (Chassis CTC 187 CK).
It appears as a pincushion problem which the customer experienced a year
before. Also it had a tendency to shutdown. When the set is turned on,
it takes a while before all four sides bounce in towards the center and
retreat to the outside. Once started, this effect perpetuates itself.
I did the normal tuner wrap. At the same time I replaced the damper
diode
CR4402, the pin diode CR4403, as well as CR4401. C4402,C4403, and C4405
checked good. The effect remain the same. However, it now took hours for
it to appear. I then replaced all the transistors on the pincushion
board
(Q4804,Q4806,Q4805,Q4851 as well as CR4851). I did not replace U4851
(LM311N). The effect remained. At this point, I began to notice when
the picture converged in and out, the on screen "Stereo" indicator would
also come on and off in timing with the convergence. At this point, I
suspected problems in the power supply. I replaced the horizontal out
Q4401, the B+ rectifier CR4106, the filter cap (which has a tendency
to go bad) C4105. I resoldered the pins on the regulator U4101 which had
been done at an earlier time. The problem still persists although it
seems to occur sooner. Has anyone ever encountered this time consuming
problem? Any help will be greatly appreciated. Thanks ahead. Ron.

 

[BWL]

May be the CPU; this set has all kinds of weird problems (no onscreen, loss of
audio, etc). RCA replacement CPU comes with the EEPROM; replace together.

 

[David]

Sounds like you missed the obvious and common starting point for the
problem. Contaminated pins on the horizontal driver transistor. Most techs
who do lots of these sets are well aware of this most common problem. If
they simply go resistive all kinds of horizontal size issues arise. If they
open up, typically the HOT will short rapidly. Plus there is a SFM resistor
on the emitter of the h-driver transistor that is known to go bad.
David

 

[Jason D.]

May be the CPU; this set has all kinds of weird problems (no onscreen, loss of
audio, etc). RCA replacement CPU comes with the EEPROM; replace together.

I would agree with this but to be 100% sure, check the I2C bus with
scope for clean signals, sufficient volts. If distorted or too low
this can happen. Can be weak 5V, conductive glue under the SMD
components that are on the I2C circuits.

This is all well with tuner grounds rework but I like to put a small
naked wire bent to L connecting to solder inside the tuner's shield to
the white ground wire stake (solder side) both are close to each other
at one corner. I put that small jumper to clear the bottom tin when
installed. Full-up jumpers per RCA is too much effort especially age
of these sets due to aging CRTs. Fewer and fewer of these onboard
tuners (17x/18x) coming in with healthy CRTs.

Did the grounds for micro ground shield? I always do both.

If you must swap these micro or eeprom or both do first thing: record
all the settings under 77 and 78 pass numbers. 76 is for deflection &
CRT adjustments but good idea to record the number 1 under 76, this is
horizontal frequency setting.

Cheers,

Wizard