You guys are missing the info!! These units will not run
with high standby B+. Scopes & EEPROM changes won't
fix it. I tried everything I could think of. Just read again. Rono.

RCA 25" M # 25GT536, chassis # CTC177AG. Unit was dead,
replaced STK-730-010 (shorted), R104 1.5 meg ohm (gone high),
C4105 10UF @ 250 Volt (gone leaky), checked/replaced CR4108
(130 volt line), changed C4402 (warped), 12 volts, & 5 volts standby
is fine, 5 volts to EEPROM, & tact switches, but 130 volt line is +146
volts dc. B+ to LA7610 main jungle IC +7 volts. B+ to horizontal output,
& drive is + 146 volts, & unit won't start. What did I miss? Rono.

See posting with binary attachment in alt.binaries.schematics.electronics
for excerpt from training manual and short description of basic SMPS
troubleshooting in the posting.

Didn't they cover SMPS basic operation in one of the electronics degree
classes?

David

"Rono" wrote in message
...
You guys are missing the info!! These units will not run
with high standby B+. Scopes & EEPROM changes won't
fix it. I tried everything I could think of. Just read again. Rono.

RCA 25" M # 25GT536, chassis # CTC177AG. Unit was dead,
replaced STK-730-010 (shorted), R104 1.5 meg ohm (gone high),
C4105 10UF @ 250 Volt (gone leaky), checked/replaced CR4108
(130 volt line), changed C4402 (warped), 12 volts, & 5 volts standby
is fine, 5 volts to EEPROM, & tact switches, but 130 volt line is +146
volts dc. B+ to LA7610 main jungle IC +7 volts. B+ to horizontal output,
& drive is + 146 volts, & unit won't start. What did I miss? Rono.

Ok Maybe a break on the board or you have missed a bad component.

kip
"Rono" wrote in message
...
You guys are missing the info!! These units will not run
with high standby B+. Scopes & EEPROM changes won't
fix it. I tried everything I could think of. Just read again. Rono.

RCA 25" M # 25GT536, chassis # CTC177AG. Unit was dead,
replaced STK-730-010 (shorted), R104 1.5 meg ohm (gone high),
C4105 10UF @ 250 Volt (gone leaky), checked/replaced CR4108
(130 volt line), changed C4402 (warped), 12 volts, & 5 volts standby
is fine, 5 volts to EEPROM, & tact switches, but 130 volt line is +146
volts dc. B+ to LA7610 main jungle IC +7 volts. B+ to horizontal output,
& drive is + 146 volts, & unit won't start. What did I miss? Rono.

Rono:
Us guys are trying to give you repair suggestions with the info you post.
You have the television in front of you with your test equipment. Standard
troubleshooting based on the info you gave would suggest SMPS problems?????
or jungle not providing startup HPulses to HDrive xstr, HDXfmr and base of
HOT. Have you scoped for startup Hpulses..... maybe that is the missing
info we are not seeing in your post.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -


"Rono" wrote in message
...
You guys are missing the info!! These units will not run
with high standby B+. Scopes & EEPROM changes won't
fix it. I tried everything I could think of. Just read again. Rono.

RCA 25" M # 25GT536, chassis # CTC177AG. Unit was dead,
replaced STK-730-010 (shorted), R104 1.5 meg ohm (gone high),
C4105 10UF @ 250 Volt (gone leaky), checked/replaced CR4108
(130 volt line), changed C4402 (warped), 12 volts, & 5 volts standby
is fine, 5 volts to EEPROM, & tact switches, but 130 volt line is +146
volts dc. B+ to LA7610 main jungle IC +7 volts. B+ to horizontal output,
& drive is + 146 volts, & unit won't start. What did I miss? Rono.

Rono whined:

You guys are missing the info!! These units will not run
with high standby B+. Scopes & EEPROM changes won't
fix it. I tried everything I could think of. Just read again. Rono.

Even if the advice you get is wrong, you should be more grateful to
this group which has answered lots of your questions. As it turns
out, the information you did receive WAS CORRECT.

RCA 25" M # 25GT536, chassis # CTC177AG. Unit was dead,
replaced STK-730-010 (shorted), R104 1.5 meg ohm (gone high),
C4105 10UF @ 250 Volt (gone leaky), checked/replaced CR4108
(130 volt line), changed C4402 (warped), 12 volts, & 5 volts standby
is fine, 5 volts to EEPROM, & tact switches, but 130 volt line is +146
volts dc. B+ to LA7610 main jungle IC +7 volts. B+ to horizontal output,
& drive is + 146 volts, & unit won't start. What did I miss? Rono.

The 177 series doesn't regulate at 130, it regulates more like 140 VDC.
This particular smps type doesn't tightly regulate the B+ at standby,
so 145-147 is normal. Once the TV starts and current loads the supply,
it will regulate to within +/- 1 volt at 140.

So if this TV fails to attempt a start with the standby voltages
nominal, you must check a couple of things (and I must repeat myself).
The micro needs to have viable clock and data lines, which need to be
checked with a scope. The micro needs 5 volts and reset line at proper
voltage, and it needs a running clock (plus more). The micro queries
the eeprom, so the SDL is active for about a second at plugin. If the
data doesn't appear at all, you have a system control problem. If the
data appears and doesn't stop after 1 second, the micro isn't
communicating with the eeprom, and is continually trying. The eeprom
could be bad (as another poster suggested), or there is an open
circuit between the micro and eeprom.

If the data appears and stops after 1 second, the system control is
most likely OK, and you need to check the horiz output pin of the T
chip for horiz drive. If it appears, follow the signal to the horiz
drive\output circuit.

If no drive appears, scope the clock and data lines to the T chip. If
they are OK, the T-chip could be bad, the horiz drive Vcc is missing,
or the horiz freq determining components off the T chip are bad.

John

You guys are missing the info!!

We are missing info that YOU must provide. If clock and data are clean,
what do you have at the collector of the horizonal DRIVER ?. Do you
have a flatline at B+, a normal waveform, or that =BC sine wave you get
when the secondary is open ?

You should be watching the scope as you try to turn it on, to determine
if it's going into immediate shutdown. This can happen silently, and
very fast.

This business is not succeeded in by remembering what it was last time.
You succeed in this business by figuring it out. Then of course you
remember it, but I simply can't be your eyes and ears, and hand to
guide the DVM or scope probe.

If you're not into scopes, the SDA and SCL lines on the EPROM should be
a few tenths under Vcc, and equal. If the discepancy is more then 0.3V
and unequal you most likely have a bad EPROM. If changed and the
symptom persists, one of the chips on the bus has a bad I2C interface.

You might just have a bad fly, the HOT waveform will tell you that.

You might also give second thought before the next time that you say
that "WE" have missed something. Last I checked now, four respodents to
your post are quite skilled (I guess that includes me in this case). I
don't really know Kip, but in this case he made a valid point, as far
as David, Dan and John go, they are definitely the kind of techs that
each successful shop needs at least one of to thrive. (or even survive)

FWIW, you need a scope and to know how to use it, then you wouldn't
have even asked the question. One positive thing, you only need about a
20Mhz scope for most TV work, they are cheap.

Don't sweat it, live and learn, learn and live.

JURB

On Mon, 23 May 2005 01:12:04 -0230, "Rono" wrote:

You guys are missing the info!! These units will not run
with high standby B+. Scopes & EEPROM changes won't
fix it. I tried everything I could think of. Just read again. Rono.

RCA 25" M # 25GT536, chassis # CTC177AG. Unit was dead,
replaced STK-730-010 (shorted), R104 1.5 meg ohm (gone high),
C4105 10UF @ 250 Volt (gone leaky), checked/replaced CR4108
(130 volt line), changed C4402 (warped), 12 volts, & 5 volts standby
is fine, 5 volts to EEPROM, & tact switches, but 130 volt line is +146
volts dc. B+ to LA7610 main jungle IC +7 volts. B+ to horizontal output,
& drive is + 146 volts, & unit won't start. What did I miss? Rono.


Rono, 146V in standby is normal. These chassis usually run between
130 to 140V B+ depending on models using this chassis.

Unsolder the transformer and measure all the resistors to be sure,
replace 10uF 63V in two locations; both are on both sides of that
STK-730, one for SMPS, one for horizontal area. I find them bad nearly
80% of time.

BUT, that can be caused by bad solder in tuner & micro grounds and
that means eeprom can be corrupt. Chipper check will fix this up by
reiniting the eeprom or replace the eeprom but that will be more
involved setting up other settings. UGH, that why I use chipper
check. and maybe have to align the tuner (57 of them for 19 channels
settings in groups of 3). Service manual is a must for consulting
when setting up eeprom contents.

By the way, get the horizontal driver transformer out and scrape pins
on it clean get waxy stuff out of holes, reinstall & resolder.
Carefully check that 2.4K off the emitter of the small SMD transistor
in the horizontal driver circuit.

Cheers, Wizard