On 13 Sep 2003 00:32:59 GMT, "Ol' Duffer" wrote:

Couple comments and a big update after this.


1. Vertical foldover is usually caused by failed bootstrap capacitor.

True, I have seen this so OFTEN in LA78xx IC series, usually running
with bad cap fries them but for some reason in RCA, this circuit
design is more tolerant of wimpy "bootstrap" but makes top drop down
cleanly appox 1" down. I called this pump up cap and customer
complaint got that fixed.

But what really get these TDA9302 & TDA8172 is bad solder connections
on IC itself (often seen this in philip sets).

2. These IC's need more drive than you might think. Input pulse
can look okay, but not be adequate if the preceding stage has
soft power supply.

Interesting, I'll check that against the schematics it has voltages
listed so will confirm.

Original repair I replaced: vertical IC & 26V supply resistor, now new
problem surfaced with this update.

Now to this UPDATE: Fixed that noisy waveform, the problem didn't go
away after I replaced that pump cap. There was open 1.5 ohm 2W
resistor that ties vertical IC output to the ground via a 0.22nF poly
cap. More like filtering than anything else. Made this looks like
bad pump but it is really noisy waveforms with lines and "foldover" at
top of screen.

Now I have new problem, Now fried that vertical IC after a minute.
Pix was PERFECT after that filter network was fixed. Burned out the
internal ramp circuit leaving retrace circuit intact and didn't burn
any of those fusible resistors.

When I have another good chassis with this type of RCA vertical
circuit, I'll beliefly uncouple that filtering network on that
vertical output and see what raw waveforms with good yoke looks like.

I do have RCA schematics for all chassis including old ctc169, 17x and
up on both cd and paper.

Cheers,

Wizard