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.
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