Tosh 55G90

What kind of TV is it?

I've killed clock and data on a running chassis a couple of years ago as a test, and the TV continued to run, but I don't remember which jungle (I think it was a Sanyo).

I figured the model number would give you that, TP55G90 is a Toshiba with a chassis in the TAC99XX series, built in the nineties.

If what you say holds true on this set, all I need to know now is the method. Force source, sink or actually interrupt the signal. ???

I am not 100% sure, but pretty sure I have also disconnected the focus from the fly, eliminating that arcing as a cause. I scoped the outputs from the jungle and they were still doing it, even though you could'nt see it on the screen. Just how did you kill clock and data ? If it helps, this set uses a TA1222 jungle and a TMPA8700 series micro (orig was a -111CN, replacement is -121CN)

Can you recommend a method to do this that is chip friendly and not prone to cause damage or flag some other fault mode, thus rendering confusion ? Others are starting to tell me to get out of the digital domain and look elsewhere, but the timing is just too perfect and steady. At the very least I would like to run one test to prove whether it's in the digital domain or not. Killing clock and data is the only way I can see. It is the only way to isolate it and get a valid yes or no.

Incedentally, since the jungle has been changed, I think just killing the data line should yield the results I need. What say you ? This is however a Toshiba chipset, not Sanyo.

I've noticed that it is constantly busy, unlike some other sets. Perhaps one of the other chips in the system is giving an improper handshake and causing a partial systyem reset. What if one is responding to the address of the jungle, but in gibberish. ?

Thank you, I think my next step is to do it, isolate, kill or shunt the data somehow.

Sidestepping myself here, why would the bus be active continuously ? There shouldn't be a valid reason for that. Quite a few chipsets address the needed parameters when you adjust the controls and then pretty much shutup, except maybe or a BLIP-BLIP, ,,,,,,, BLIP-BLIP.

Why would the bus have to be so busy when you are not chaging anything, nor even addressing any functions ? XDS maybe ?

I guess it is possible, but I'm not sure if this set even has XDS. Might be too old.

I see no bus expander or MUX/DEMUX chip around, maybe that's why there is always activity ? Now we're back to why I put a $120 micro in it. Could this be one of those rare times I should go into the options mane, write down the settings and start turning things off ? Perhaps someone has been in there.

It looks like the EPROM has been changed, maybe the guy who did it threw the "special instructions" in the trash which said "Make sure you set option code CS02 to 0F0 before attempting to autoprogram the set. Failure to do so will make it nessecary to replace the EPROM and perform this function as described herein.

Failure to do so may result in a blanking of the video every 8.37341 seconds."

That would floor me, and I don't think it's likely, but it is entirely possible.

If this is what the game has become so be it.

Thanks again.

JURB

Hehe...my bad. I looked at the post, not the title.

I did it by unsoldering the SDL and SCL lands at the IC, leaving the 5v pull up resistors intact on the board. I temporarily reconnected them with a couple of common sewing pins, and pulled them out once the TV was up and running. As for whether it would be chip friendly, I can only say that it didn't do any harm to the one I tried. Your mileage may vary. :)

you

Oh boy, don't you love tackling something that's already been futzed with? I've had several TVs with bad eeproms that I could restore partial or even full operation by temporarily removing the eeprom from the circuit (RCAs obviously are the glaring exception) as a test. I'd try it in your case. If the flashing goes away, there may be an option bit that may need to be set.

John

with?

I'm lucky thus far, everybody who worked on it was competent. I know them. Nobody has any more ideas. They didn't give up easily, and neither will I, but I'm here now and it's in my lap.

I did say the EPROM looks like it's been changed, or at least the solder does. Not bad but it's shinier. I wonder just how many sets can run with no EPROM. Last one I can be sure of is a CTC140. Maybe a CTC169.

It's very interesting you bring this up, here's a true anectode for ya: One day I got your typical tuner grounds and EPROM job on an RCA. However it happened I changed the EPROM with the set plugged in. Fired the set up and it was exactly like it was before. I expected the H freq to be out etc., until I realized that I hadn't unplugged the set.

I'm getting close to thirty years in this gig, and that has happened more than once. More than half of the times no damage ocurred (though I'll never be able to explain why for sure)

It's got to be a combination of luck and my soldering technique. I can change a 64+ pin IC maybe ten times without collateral damage, but I don't think that's special. I think most techs should be able to do it. In some cases maybe the thing was dead shorted anyway so nothing I could do could zap anything, except me of course.

This is what happens when you get called away from the bench for other matters.

I will figure out a way to stop data from getting to the jungle IC, I need to prove I'm on the right track now, or back up.

Of course at this point I have eliminated or checked so many things I really don't know what exactly I should back up to !

Even if interrupting data to the jungle stops the symptom, now could it possibly be any chip on the bus ? Micro, jungle and EPROM ruled out, then what, take the tuner out ? Find the audio processor, closed caption and possibly even XDS ?

What a game. In coming years I can see we are going to need drastically better methods.

I need to know for sure if it's digital, but I'm not going to attack the EPROM yet because it has no problem storing parameters.

Hmmmmmmmmmmmmmmmmmmmm

Just thought of something. What if it's set to 50Hz sweep ? Could it be triggering the vertical alright but runs out of range and blanks when it THINKS it's resetting the sync countdown ? It is not though, the OSD is perfectly stable and remains interlaced, but maybe it THINKS it's out of sync ?

I will try what we have discussed, but first I think I'll have one more look at the service menu.

I might have to temporarily turn this job away, but I am by no means scared of it. Remember I'm the one who had to adjust vertical centering to fix a problem with greyscale, and had to reconnect a speaker to get high voltage.

While I like the challenge, there is a customer out there waiting.

Thanks again, I'll let you know how the results of what I do next turn out.

JURB

Aha ! ;

Disconnection the SDA line to the jungle stops the problem.

I have reconnected it and thusfar have disconnected everything I could find on those lines (SDA1 and SCL1) to no avail. Neither print that I have matches, but between the two of them I got enough on the chipset to proceed. There is some kind of "level shifter" circuit between SDA/SCL1 and 2 so I copmpletely isolated them. All of this didn't affect the problem. I even disconnected the tuners and sure enough, the snow was blinking out every eight seconds.

There is a rather large "OSD processing IC" something 90091 (MB ?) which I DLed the datasheet for but was having a hard time IDing the SCA/SDL, I think it's processed partly somewhere else, but I did lift the pins of all the Vccs to it but it still didn't fix it.

I think on my next runin with this dog I'll actually disconnect the SDA1 pin from the micro. The reason that I didn't head for the EPROM is that it does not share the SDA/SCL and there is no constant activity on the bus. Of course it could be telling the micro to do something wrong, so if the SDA from the micro interrupted stops it, it probably is the EPROM.

Next time around it'll be another thread, we're going to get some money made the reat of the week if possible.

Thanks again.

JURB

The fix is to initialize the eprom. Follow the proceedure that is outlined in the service manual for replacement of QA02

Cheers

Jim