DIYbanter - RCA TV model 20541, chassis CTC203J2 with Excessive Reg B+

On Tue, 07 Oct 2008 14:11:55 GMT, (Brad) put
finger to keyboard and composed:

Hi,

I have a 20" screen RCA TV model J20541, chassis CTC203J2
(mfg 10/00) in my service shop (no SM).

TV tries to go on, but turns right off due to excessive HV. The
regulated B+ measured +154V which is too high.

I tested some parts in the voltage regulator circuit, but without a
schematic, I am "handicapped".

Did anyone fix a similar problem with this or similar chassis TV?

Thanks in advance, Brad

There is this old thread in the Google Groups archives:
http://groups.google.com/group/sci.e...1d1f36e403d846

It suggests that the fault may be in the feedback circuit on the
secondary side.

There is also the following manual at eserviceinfo.com.

148 page Thompson Consumer Electronics (RCA & GE) technical training
manual for RCA ProScan color TV model # CTC203:
http://www.eserviceinfo.com/download...CA_CTC203.html

I don't know how relevant the above manual is to your chassis, but I
notice that the manual does not specify a value for B+, which suggests
to me that it may vary between versions. Anyway, it looks to me from
the values of R14115 (143K), R14116 (2K), and R14126 (37.4K) that the
B+ in standby mode should be about 190V. In run mode the B+ is about
5% less, ie 181V (= 2.5V x 145K/2K). Your chassis, if it is similar,
may use different resistor values, and a different B+.

If you are seeing a B+ voltage which is about 10V too high in run
mode, then I'd check the +13Vr and +16Vs supply rails. Have you
checked C14101 (2.2uF)?

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.