"Jason D." bravely wrote to "All" (10 Sep 03 03:48:33)
--- on the heady topic of "Big battle with WEIRD vertical deflection problem in =
PTK195 chassis."

If there are spikes in the output ramp then it would seem like a supply
filter electro problem to me. Have you checked what the supply noise
looks like on the scope? If not then the pump up might be off value.


JD From: (Jason D.)

JD Quickie on the type of vertical circuit:
JD For others who isn't famillar with this PTK195 as well as CTC197
JD chassis, this vertical circuit is virtually same in CTC17x, 18x, 203
JD and up using TDA8172 vertical IC.

JD This set came in with blown vertical IC and a very crispy 1 ohm 2W
JD resistor (snapped in two when I took it out) for 26V supply to the
JD vertical only. Fixed that up. Gee that's a FIRST for me to actually
JD have to replace that in RCA in my 1 and half years for a shop.

JD Well! This one really got me stumped, top most is bowed in,
JD non-linear lines and all shaking like mad while most of pix is
JD perfect. Got all my tools on that (scope, dmm and ESR meter) All the
JD 26V and 13V supplies are quiet and smooth, caps checks good EXCEPT: on
JD scope on output of vertical IC I see this like this:

JD Retrace pulse as it should be, then a normal clean ramp down to appox
JD mid way then I see high frequency noise centered around that ramp down
JD to the bottom just before the retrace pulse I see few sharp tall thin
JD spikes. Reminds me like this imagine chroma waveform without steps
JD with half top the pix b/w and half bottom in color.

JD Even I subbed a good yoke on each of R, G, G yoke connectors in turn
JD with no luck hoping to catch a bad yoke.

JD When this that JURG6006's came up with this vertical IC problem on
JD "Subject: Mit. VS5010 intermittent shutdown" my attention snapped up
JD and had to post mine too.

JD That vertical noise is confusing the top convergence area so bad that
JD top part is jumping around: straight and bowed irratically.

JD BTW: I tried another RN14501 with no luck, the sawtooth input is
JD clean at that RN14501.

JD Cheers,

JD Wizard

.... Resistance Is Futile! (If 1 ohm)

On Wednesday, 10 Sep 2003 09:34:32 -500, "Asimov"
wrote:

"Jason D." bravely wrote to "All" (10 Sep 03 03:48:33)
--- on the heady topic of "Big battle with WEIRD vertical deflection problem in =
PTK195 chassis."

If there are spikes in the output ramp then it would seem like a supply
filter electro problem to me. Have you checked what the supply noise
looks like on the scope? If not then the pump up might be off value.


In RCA's PTK195 (based on CTC195) projector still under warrenty:

Came in with blown vertical IC and crispy 26V supply resistor changed
both and saw noisy waveforms.

Changed pump cap, no difference, finally found the 1.5 ohm 2W is open.
This resistor is connected to .22nF 100V to ground from the output of
TDA8172 vertical IC. Changed both cap and resistor. Got perfect
vertical waveforms. Now I have a cooked vertical IC after a minute.
Now I know why: one of yoke is bad.

RCA using this vertical IC TDA9302 and TDA8172 very rarely blow so if
you see one with blown one, be suspicious because this is when
something is killing that vertical IC. A half-dried pump cap doesn't
faze vertical IC, customer complaint with squished top pix got that
fixed instead. Usually often is tuner & micro grounds if the pump cap
isn't the problem.

Back to this damned projector, how can I tell which yoke is guilty?

Cheers,

Wizard

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