DIYbanter - RCA RPTV: Chassis #PT169PGA Dead!!!

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RCA RPTV: Chassis #PT169PGA Dead!!!

Hello,
I'm working on a RCA RPTV, Chassis #PT169PGA. The problem is that it is
completely dead. I haven't had much experience with this chassis before, so
I'm asking for some assistance in troubleshooting it. I do not have a
schematic for this chassis. The problem that I am having is that I do not
have any secondary voltages at all, including no B+. I have the main
chassis board removed from the cabinet and I also have the HV lead
disconnected from the HV splitter and it is covered up in a paper towel tube
so I won't get zapped with 30KV. Will I be able to troubleshoot the power
supply of this TV without it being connected to the other connecting
boards??? I do have it connected to the external power supply board too.
Anyone have any suggestions or ideas on where to start looking for
problems??

Thanks!

Rocker wrote:

Hello,
I'm working on a RCA RPTV, Chassis #PT169PGA. The problem is that it is
completely dead. I haven't had much experience with this chassis before, so
I'm asking for some assistance in troubleshooting it. I do not have a
schematic for this chassis. The problem that I am having is that I do not
have any secondary voltages at all, including no B+. I have the main
chassis board removed from the cabinet and I also have the HV lead
disconnected from the HV splitter and it is covered up in a paper towel tube
so I won't get zapped with 30KV. Will I be able to troubleshoot the power
supply of this TV without it being connected to the other connecting
boards??? I do have it connected to the external power supply board too.
Anyone have any suggestions or ideas on where to start looking for
problems??

1. find a recent post from Sam Goldwasser here and find the URL for his
electronics repair FAQ. *read it* preferably at least twice. Feel free
to skip the Laser and small engine FAQs. If that doesnt give you some
ideas where to start with an unfamiliar D.O.A. chassis, you probably
shouldn't be trying this career.

2. 30KV will jump right through a paper towel tube and directly to the
nearest grounded object which could be you. If I need to run a chassis
with the EHT lead off, I always put the end in a 1 pint beer glass,
which is empty and absolutely clean (I always polish it inside and out
with some kithen paper moistened with methylated spirits before use).
The beer glass sits in a tin that I connect to the ground strap on the
tube just incase the glass should break down. I stay well away from the
glass as well. If you need to, a clothes peg is good for keeping the
lead in the glass.

3. We dont get many projection TVs over here, especially not with
seperate power boards but I have tested many 28" and bigger old Sony PSU
boards with a 240V 100W incandescent lightbulb as a load on the +B line.
Other brands didn't usually have a seperate power board. If you are
expecting more than 110V on your +B I'd suggest 2 110V bulbs in series.

N.B. Many psus now have a control signal to put them in and out of
standby. If you are lucky this will be a voltage level but I've seen
quite a few recent sets where the microcontroller actually provides
drive pulses to the PSU chopper so the set wont run if the
microcontroller senses a fault. Usually there is either a seperate
standby transformer or some arrangement to make the PSU run for a couple
of cycles when the supply is connected to get some juice to the
microcontroller. The nastiest I've seen lately only powered the remote
reciver and the front panel button matrix and any pulse from them
triggered a brief burst from the PSU so the microcontroller could decide
wheter to stay on or shut back down. Needless to say, it was a real
bitch to troubleshoot even with the diagram.

4. It is almost always a bad idea to try to run a chassis witout all the
scan coils connected unless you have disabled the line output stage.

I hope for your sake someone who knows your chassis is listening :-)

--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk [at]=@, [dash]=- &
[dot]=.
*Warning* SPAM TRAP set in header, Use email address in sig. if you must.

Completely dead, no secondary voltages at all; check for shorted horiz output
transistor or caps near it; if OK, rebuild power supply (several suppliers make
kits with most of what you'll need). This set has 140+ volts on horiz output
while in standby, be CAREFUL!!!

On Mon, 13 Dec 2004 16:04:12 -0600, "Rocker" wrote:

Hello,
I'm working on a RCA RPTV, Chassis #PT169PGA. The problem is that it is
completely dead. I haven't had much experience with this chassis before, so
I'm asking for some assistance in troubleshooting it. I do not have a
schematic for this chassis. The problem that I am having is that I do not
have any secondary voltages at all, including no B+. I have the main
chassis board removed from the cabinet and I also have the HV lead
disconnected from the HV splitter and it is covered up in a paper towel tube
so I won't get zapped with 30KV. Will I be able to troubleshoot the power
supply of this TV without it being connected to the other connecting
boards??? I do have it connected to the external power supply board too.
Anyone have any suggestions or ideas on where to start looking for
problems??

Thanks!

That's probably the most common television chassis ever produced. (At least in
my area) You should have 140V and 15V in standby, even before the set's powered
up. If it's missing, or the wrong voltage, that will need to be corrected first.
Also, make sure the H.O.T is not shorted. Once the standby voltages are
stabilized, only then should further troubleshooting be attempted.

Alan Harriman

OK...I have been working on TV's for the last 25 years or so and I do it as
a hobby. I know what to touch and what not to touch when servicing TV's.
Now...the problem I am having is this...I do not have any secondary voltages
whatsoever. Which means no 15V stand-by or 140V B+. The main problem I have
is that I don't have a schematic. I have a CTC169JS6 schematic which has
some of the power supply circuitry but isn't the same. The chopper circuit
is working , but the 10 us pulse that is needed for pin 2 for the PWM isn't
there. Where is this pulse generated from? Does anyone here have a schematic
of this power supply that I can get a e-copy of??? Thanks so much for any
more help or assistance you can provide.

Mac

"Alan Harriman" wrote in message
...
On Mon, 13 Dec 2004 16:04:12 -0600, "Rocker" wrote:

Hello,
I'm working on a RCA RPTV, Chassis #PT169PGA. The problem is that it is
completely dead. I haven't had much experience with this chassis before,
so
I'm asking for some assistance in troubleshooting it. I do not have a
schematic for this chassis. The problem that I am having is that I do
not
have any secondary voltages at all, including no B+. I have the main
chassis board removed from the cabinet and I also have the HV lead
disconnected from the HV splitter and it is covered up in a paper towel
tube
so I won't get zapped with 30KV. Will I be able to troubleshoot the
power
supply of this TV without it being connected to the other connecting
boards??? I do have it connected to the external power supply board too.
Anyone have any suggestions or ideas on where to start looking for
problems??

Thanks!

That's probably the most common television chassis ever produced. (At
least in
my area) You should have 140V and 15V in standby, even before the set's
powered
up. If it's missing, or the wrong voltage, that will need to be corrected
first.
Also, make sure the H.O.T is not shorted. Once the standby voltages are
stabilized, only then should further troubleshooting be attempted.

Alan Harriman

I have worked on several tons of this chassis .Check all secondary
diodes for short, Be sure HOT is not shorted. be sure chopper trans is
not shorted, see if have raw B+ on output if bridge rect. If all this
is ok check voltage on pin 16 of U4101 regulator IC should be around
11 volts If low IC probally shorted. I never turn this set on untill I
have proper standby voltage approx 146-148V On regulated line If you
get B+ voltage and it is high check C4102 2.2 mf off pin 6 of U4101
also check C4108 a 47 or 39 mf cap off the base of chopper xistor. Let
me know how you come out on this if nessary I can email power supply
schematic After over 54 years of TV service on primaraly RCA i'm very
comfortable with this set Charles Grob

Go here if what Charles has said ( Which should fix you up ) does not.

http://wa6ati.com/Ctc169.htm

kip

Also replace the 15uf cap that sit's next to the 2.2 charles mentioned. Some
sets use different values, all go bad the same way.
Go here if what Charles has said ( Which should fix you up ) does not.

I have worked on many 169 chassis. In your case as someone else said do
not try to fire up chasis with out yokes connected. Remove the entire
light box (with all cir bds & crt's main chassis can be slid out to be
worked on, May have to lenghten ground wire from chassis to HV Div
Block. 1st check raw B+ off the bridge rect Around 170v DC, check all
secondary rectifiers, Hor Out Xistor, chopper xistor,for shorted
condition. Do all this before trying to turn on. Next check standby B+
should be 143-146 v. if not there check pin 16 of U4101 IC should be
around 11v if very low IC is defective, If standby v is high check 2.2
mf off pin 6 of ic, also check 39 or 47 mf cap in base cir of chopper.
These are the most common problems, feel free to contact me for further
info if needed. Also if all chassis not interconnected set will not
have light on crt's (safety cir)
I could email schematic of power supply if you like, you really do need
it Charles Grob

This particular chassis has a 470pf cap in parallel with both CR4101 &
CR4106. According to the website that kip referred me to, these caps are
2.2uf electrolyctic. Did RCA put out a service bulletin updating these
values????.

"john" wrote in message
.. .
Go here if what Charles has said ( Which should fix you up ) does not.

http://wa6ati.com/Ctc169.htm

kip

Yes...I agree that C4102=2.2uf@100V and that C4104=15uf@63V and the cap to
the base of the chopper transitor is 39uf. However in the
http://wa6ati.com/Ctc169.htm website it says several times the following:

"I asked tech to connect his meter to the cathode of CR4116, then apply
power. The voltage shot up to 178 volts then began to drop. This indicated
there is no comparison voltage from the switch mode transformer to the Stand
by voltage sense input of the regulator U4101. I instructed tech to replace
CR4106 with the smaller of the two diodes & CR4101 with the larger diode in
the 207878 kit, plus replace C4103 a 2.2 mfd@100vdc. Unit was fixed with
these components.".

The cap in question here is C4103. The schematic that I have for a CTC169
chassis says that C4103= 470pf, 100V cap. So that's why I was questioning
which value was correct! Thanks!!!

"RonKZ650" wrote in message
...
This particular chassis has a 470pf cap in parallel with both CR4101 &
CR4106. According to the website that kip referred me to, these caps are
2.2uf electrolyctic. Did RCA put out a service bulletin updating these
values????.

You must not be looking at the right caps. 2 capacitors directly to the
left of
the reg driver IC need replacement, most are 2.2uf and 15uf, and one
capacitor
an inch or so to the right of the chip which is either a 39uf or 47uf.
They all
use electrolytics.