LA 7612N - RCA jungle IC

[Arnold stewart]

Re: RCA Chassis CTC197CE2, Model F32683SB
The jungle IC is an LA7612N. TV has sound but no video & no OSD.
Orignially TV would click three times and do nothing. I changed the
flyback. Now I have a raster & sound, but no video. Does anybody know if
the LA7612N has the same pinouts as the LA7610? If not, could you tell
me what pins have the RGB outputs? (I may also have a corrupted eeprom,
however TV turns on, changes channels, & volume functions normally.)

 

[JURB6006]

Go to bdent.com and get a user and pass, it's free. You can also get datasheets
at datasheetarchive.com, but they are slow. Might not matter if you're on wire,
but if you got highspeed internet, is't, well, like the old days. Very slow.

You're probably headed in the right direction though, wouldn't be the first
time a bad fly fried the ABL network and blew out the video circuit.

JURB

 

[Arnold stewart]

I've tried bdent.com They don't have anything on the LA7812. I'll try
datasheetarchive.com
Thanks.

 

[David]

I think what you will find (in the far reaches of my memory) will be
either a shorted zener or open resistor on the ABL line, or a missing
h-sync return pulse to the system control for that symptom on that
chassis.

David

 

[Boris]

Hey Arnold,
Have you read "RCA/GE TV (CTC175-187+) Solder Connection and EEPROM Problems" - it basically says that RCA EEPROM problems are very
common and can extend to much more than trivial outcomes. However, I do tend to agree with you that it is very unlikely that only
the video is completely out due to bad EEPROM.
http://www.repairfaq.org/sam/rcatune.htm

It may also be useful to take a look at the RCA197 service manual
http://schforfree.seedhost.com/archive/?path=Video/products

I would like to use this post to also ask a few enlightenment questions:
1. What is the function (and acronym) of the ABL circuit? Perhaps I know about it, but confuse the English name, or might have never
heard of its function...
2. How do you "change the flyback"? Do you mean the cable or the whole transformer? I've heard people referring to the fat red
high-voltage cable as "flyback" and it (typically) cannot be changed. In this case, is there a special term for the big transformer,
tied to the HOT collector?
3. Regarding David's message: "missing h-sync return pulse to the system control" - where is this pulse taken from? What's the
purpose - feedback that the HOT is working fine?
4. I've heard there is a way to cut off the HOT circuit, connect a regular bulb and test the power supply alone. I never dared to do
that, however, being afraid of corrupting a feedback from the HOT to the power supply and blowing off the whole TV/monitor. Can
onyone comment how does this bulb trick work (may be a detailed link)?

Best regards,
Boris

 

[Arnold stewart]

Hey Arnold,
Have you read "RCA/GE TV (CTC175-187+) Solder Connection and EEPROM
Problems" - it basically says that RCA EEPROM problems are very common
and can extend to much more than trivial outcomes. However, I do tend to
agree with you that it is very unlikely that only the video is
completely out due to bad EEPROM.
http://www.repairfaq.org/sam/rcatune.htm

It may also be useful to take a look at the RCA197 service manual
http://schforfree.seedhost.com/archive/?path=Video/products

I would like to use this post to also ask a few enlightenment questions:
1. What is the function (and acronym) of the ABL circuit? Perhaps I know
about it, but confuse the English name, or might have never heard of its
function...
2. How do you "change the flyback"? Do you mean the cable or the whole
transformer? I've heard people referring to the fat red high-voltage
cable as "flyback" and it (typically) cannot be changed. In this case,
is there a special term for the big transformer, tied to the HOT collector?
3. Regarding David's message: "missing h-sync return pulse to the system
control" - where is this pulse taken from? What's the purpose - feedback
that the HOT is working fine?
4. I've heard there is a way to cut off the HOT circuit, connect a
regular bulb and test the power supply alone. I never dared to do that,
however, being afraid of corrupting a feedback from the HOT to the power
supply and blowing off the whole TV/monitor. Can onyone comment how does
this bulb trick work (may be a detailed link)?

Best regards,
Boris

Thanks for the website. In reply to your questions:
1. ABL stands for automatic brightness limiter.
2. In changing the flyback the whole transformer is replaced.
3. The pulse is taken from the flyback transformer and used by the
system control.
4. By removing the horizontal output transistor you will no longer get
high voltage, but the power supply will not have enough load on it to
tell you if it's working properly. Connecting a 100 watt light bulb
between ground (or emitter of the HOT) and collector, sufficient load is
placed on the power supply.

 

[ArnoldStw]

Re: RCA Chassis CTC197CE2, Model F32683SB
The jungle IC is an LA7612N. TV has sound but no video & no OSD.
Orignially TV would click three times and do nothing. I changed the
flyback. Now I have a raster & sound, but no video. Does anybody know if
the LA7612N has the same pinouts as the LA7610? If not, could you tell
me what pins have the RGB outputs? (I may also have a corrupted eeprom,
however TV turns on, changes channels, & volume functions normally.)

I have obtained much more information since this post. The LA7610 and
LA7612 do not have the same pinouts.
In my original post I said that I had a raster but no video. What I
should have added is that I had a raster with retrace lines visible on
the screen no matter where I set the screen control on the flyback,
that is until the screen was extinguished. The screen control can
adjust the voltage from 0 to approx. 550V
I have checked all voltages to the CRT and they check out normal. I
suspect I have a shorted tube.
As far as the set clicking three times and then doing nothing, RCA
explains it this way:
Dead Set - Degauss Relay clicks
If the television tries to start three times and then stops (you can
hear the clicking sound of the Degauss relay energizing), this means
the EEPROM (U13102) and T4 Chip (U16201 - LA7612) are working
(hardware is OK). Therefore the problem is most likely power supply
and/or deflection related.

 

[john]

Make sure that when you installed that flyback that none
of the small parts near the flyback got sucked in your solder sucker.
Those around the base pads...
Also make sure that filter cap to the left does not have a broken trace.

kip