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

[Brad]

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

Before you type your password, credit card number, etc.,
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[Franc Zabkar]

On Tue, 07 Oct 2008 14:11:55 GMT, bpetria@verizon.net (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.electronics.repair/browse_thread/thread/32d506ba1116e361/a91d1f36e403d846?lnk=st&q=#a91d1f36e403d846

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/downloadsm/31473/RCA_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.

 

[Brad]

Hi Franc,

C14101 in this chassis is a .82uf non-electroylitic type of capacitor which
tested good.

I checked 13Vr source components (good), but not 16V yet.

I downloaded CTC203 *. RAR (part1) from www.eserivce.info.com, but there
is an error reported by "UnPacker" (handles .RAR files).

If I repair this TV, I will let everyone know what caused this problem.

Brad

On Wed, 08 Oct 2008 06:05:04 +1100, in sci.electronics.repair you wrote:

On Tue, 07 Oct 2008 14:11:55 GMT, bpetria@verizon.net (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.electronics.repair/browse_thread/thread/32d506ba1116e361/a91d1f36e403d846?lnk=st&q=#a91d1f36e403d846

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/downloadsm/31473/RCA_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

 

[Franc Zabkar]

On Wed, 08 Oct 2008 16:26:00 GMT, bpetria@verizon.net (Brad) put
finger to keyboard and composed:

Hi Franc,

C14101 in this chassis is a .82uf non-electroylitic type of capacitor which
tested good.

I checked 13Vr source components (good), but not 16V yet.

I downloaded CTC203 *. RAR (part1) from www.eserivce.info.com, but there
is an error reported by "UnPacker" (handles .RAR files).

If I repair this TV, I will let everyone know what caused this problem.

Brad

I managed to unpack the archive with Winrar, but you need to download
all 6 parts first.

http://www.eserviceinfo.com/download.php?fileid=31473
http://www.eserviceinfo.com/download.php?fileid=31474
http://www.eserviceinfo.com/download.php?fileid=31475
http://www.eserviceinfo.com/download.php?fileid=31476
http://www.eserviceinfo.com/download.php?fileid=31477
http://www.eserviceinfo.com/download.php?fileid=31478

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

 

[Brad]

Hi Franc,

I downloaded all parts and now I have the manual (THANKS).

I have to work on other TVs now. I will go back to that one later.

ERROR in Model Number:

The model number is J20541 (I forgot the "J").

Brad


On Thu, 09 Oct 2008 06:53:51 +1100, in sci.electronics.repair you wrote:

On Wed, 08 Oct 2008 16:26:00 GMT, bpetria@verizon.net (Brad) put
finger to keyboard and composed:

Hi Franc,

C14101 in this chassis is a .82uf non-electroylitic type of capacitor which
tested good.

I checked 13Vr source components (good), but not 16V yet.

I downloaded CTC203 *. RAR (part1) from www.eserivce.info.com, but there
is an error reported by "UnPacker" (handles .RAR files).

If I repair this TV, I will let everyone know what caused this problem.

Brad

I managed to unpack the archive with Winrar, but you need to download
all 6 parts first.

http://www.eserviceinfo.com/download.php?fileid=31473
http://www.eserviceinfo.com/download.php?fileid=31474
http://www.eserviceinfo.com/download.php?fileid=31475
http://www.eserviceinfo.com/download.php?fileid=31476
http://www.eserviceinfo.com/download.php?fileid=31477
http://www.eserviceinfo.com/download.php?fileid=31478

- Franc Zabkar

 

[Brad]

Hi,
UPDATE:

I didn't locate the source of the problem (see below) after testing many
parts, but I used a "patch", after the owner gave permission, to restore the
proper B+, which I assume is +130V (HV now around 25KV). Note: I do
not have SM.

"Patch" to Restore Reg B+ to 130V:

880K (resistors combo) across R14115, 143K.

Thanks to Franc Zabkar for the training manual source (see below).
It has partial schematics.

I found a few others on the web that had the same problem, one
had exactly the same "+154" volts, however no one posted a solution. One
person said he had that problem and he said the problem lies on the secondary
side of the transformer in the feedback circuit, but he didn't say what
part(s) he replaced (if he fixed it?). Of course, this is what I suspected in
the beginning, and I checked many parts in the feedback for the
regulator, also the regulator reference circuit, and many parts around the
regulator on the primary side. I checked +13V and +16V sources, which were
about a volt+ high until I installed the "patch".

Next, I would have to replace semi-conductors, although I tested them in
circuit, to see if one of them is the problem, but there is a limit to how
much time, and the customer is willing to pay me to fix this 20" TV. I
already spent too much time on this repair project.

Brad

On Tue, 07 Oct 2008 14:11:55 GMT, Brad wrote:

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

Before you type your password, credit card number, etc.,
be sure there is no active keystroke logger (spyware) in your PC.

Response from Franc regarding the source for the training manual:

I managed to unpack the archive with Winrar, but you need to download
all 6 parts first.

http://www.eserviceinfo.com/download.php?fileid=31473
http://www.eserviceinfo.com/download.php?fileid=31474
http://www.eserviceinfo.com/download.php?fileid=31475
http://www.eserviceinfo.com/download.php?fileid=31476
http://www.eserviceinfo.com/download.php?fileid=31477
http://www.eserviceinfo.com/download.php?fileid=31478

- Franc Zabkar
--

 

[Franc Zabkar]

On Mon, 13 Oct 2008 20:13:23 GMT, bpetria@verizon.net (Brad) put
finger to keyboard and composed:

I didn't locate the source of the problem (see below) after testing many
parts, but I used a "patch", after the owner gave permission, to restore the
proper B+, which I assume is +130V (HV now around 25KV). Note: I do
not have SM.

"Patch" to Restore Reg B+ to 130V:

880K (resistors combo) across R14115, 143K.

I would have measured the values of the three resistors (R14115,
R14116, R14126) and computed the expected B+ voltages in run and
standby modes. The junction of the potential divider would be at 2.50V
in all modes, and R14126 would be switched out of circuit in run mode.

AFAICS, a clue as to what is happening would be in whether or not the
B+ rail drops when switching from standby to run mode. If not, then
one or the other of the +16Vs or +13Vr transistors could be faulty.

It seems to me that if one of the components is marginal, then your
kluge may come back to bite you if that component deteriorates
further.

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