Panasonic 27" Picture Problem

[Krankshaft]

Now here is a real wierd problem I have a Panasonic 27" CRT.

When I power it up I get sound the OSD channel selector appears I hear sound I can even bring up the OSD to adjust things but there is no picture.

Since I am getting sound for the selected channel the tuner is probably working fine.

Any ideas on this one?

The only thing I can come up with is a bad solder joint or dead section on one of the LSICs.

[PlainBill]

Re: Panasonic 27" Picture Problem

It would be fun to have a schematic and work this out in detail. Maybe a model number?

Your deductions so far are correct. The tuner and IF strip must be good if you have sound. With OSD you know that the CRT drive circuitry is good. What does that leave? You're right again, the most likely culprit is the video processor IC, or a component associated with it.

Now, does the set have video / input jacks? If so, try hooking something up to them and see what happens.

PlainBill

[i4004]

Re: Panasonic 27" Picture Problem

>Now, does the set have video / input jacks? If so, try hooking something up to them and see what happens.


exactly.

[Krankshaft]

Re: Panasonic 27" Picture Problem

Sorry for the lack of info been through one hell of a reformat toasted video card because of dead fan, bad hard drive with 4 bad sectors placed precisely to mess up the XP install, etc etc .

It's model number is CT-27G7DF

Chassis Number: JP363

Never thought to test out of component inputs. When I plugged my digital camera into the component input I again got sound but no picture.

I hope it's not the processor IC they are all SMT.

I can do it but I hate SMT . I'd rather drink a cup of acid after chewing on a razor blade .

[Wizard]

Re: Panasonic 27" Picture Problem

Do defineatly need service manual (full schematic).

Focus on jungle IC that take signals from all the sources (tuner, component, video, s-video) etc and output to the CRT board.

Make sure you have good soldering joints. Panasonic are famous for this and make sure there is no vertical problem as panasonic shut out the picture when vertical collapses enough.

Use solder quik to lift the SMD ICs.

Cheers, Wizard

[Krankshaft]

Re: Panasonic 27" Picture Problem

Wow that chip quick is pretty cool better pick some up.

Well I guess it's time to go hunting for cracked joints and fork it out for a service manual.

I had a vertical problem a few weeks back but it just turned out to be the power pin on the vertical IC cracked. I desoldered and resoldered the entire vertical IC.

FYI when the vertical goes out the video is cut from the CRT but the OSD is still visible on the vertical no sweep line.

[PlainBill]

Re: Panasonic 27" Picture Problem

I can do it but I hate SMT . I'd rather drink a cup of acid after chewing on a razor blade .

OK, tell us how you REALLY feel about smt?

PlainBill

[Toasty]

Re: Panasonic 27" Picture Problem

>>bad hard drive with 4 bad sectors placed precisely to mess up the XP install,<<

HDD Regenerator

I have an older FREE copy if you need. Have recovered many bad drives with this.

[Krankshaft]

Re: Panasonic 27" Picture Problem

Well I got the schematics I cut down the pdf so you don't have to download it all.



There is one LSIC that does everything it has 2 RGB outputs one for the OSD and one for the video signal. Oddly enough with no coax cable connected the OSD jitters with the snow that is not visible.

I have gone over it with a fine tooth comb and a strong magnifier looking for cracked solder joints I have even touched up the all of the SMT leads nada.

I'm thinking that I should replace IC001 a M65580MAP103 the EVERYTHING accept SAP audio decoding signal processing IC.



What do you guys think?

[i4004]

Re: Panasonic 27" Picture Problem

what happens if you bring external composite video signal and select it via remote (signal that goes to pin 20)?

[Krankshaft]

Re: Panasonic 27" Picture Problem

The same happens sound but no video.

[PlainBill]

Re: Panasonic 27" Picture Problem

That looks like the probable candidate. I'd say if the supply voltages look good and the surrounding components check out, that's the part to replace. Looking at the block diagram the external video signal and the video from the tuner come to this IC, are processed, then OSD is added. And it doesn't look like many external components are involved.

Now of course the problem is finding the part. I don't think Radio Shack carries them.

PlainBill

[kc8adu]

Re: Panasonic 27" Picture Problem

do you have a scope?
make sure there is video reaching that chip.
could be a switch issue or blanking due to bad vertical.
turn up the g2 and see if screen is full and no foldover,bad linearity,ect.
these chips seldom fail and when they do ist usually due to lightning.
i recently replaced a crt in a zenith system 3 for a customer.2 weeks later it lost video.problem was a small lytic that leaked and ate the traces near it.the juice wicked through the holes in the board and ate 2 small traces.

[Krankshaft]

Re: Panasonic 27" Picture Problem

Come to think of it a few weeks back it lost vertical sweep so I desoldered and resoldered the vertical IC. When it did though it blanked the video however the OSD was exempt and I saw it as a thin line.

I'll check that out.

Yeah I've got a Tek 475 and an iso transformer so I don't fry it or myself for that matter.

According to my tracing from the tuner the input video signal is TV IN (pin 26) right?

About 8 pins or so are covered by a gray silicone for some reason I guess I'll Dremel wire wheel it off if it's covering this pin.

There is a convienent test point at the tuner so I guess I'll probe there first then probe at the IC for the signal to see if it's there. In the back of the manual they list the proper waveform for comparision.

[i4004]

Re: Panasonic 27" Picture Problem

>According to my tracing from the tuner the input video signal is TV IN (pin 26) right?

yes, you also have that on ic datasheet...also check when composite is hooked, ie pin20, does it reach this ic?

[PlainBill]

Re: Panasonic 27" Picture Problem

Interesting. The schematic shows TV in is 26, Ext in is 20; s-video in is 22 and 24. The datasheet pinout agrees, the block diagram has Ext in as 20, TV in as 22, and s-video in as 24 and 26.

PlainBill

[Wizard]

Re: Panasonic 27" Picture Problem

Yes, turn up screen a bit to make raster show up and see anything that could point to vertical issues. Turn back down to original setting.

And before you condemn the IC. Go over with the scope first from inputs/tuners all the way to the IC and beyond. Input color bars so you get nice stairstep waveforms.

Cheers, Wizard

[Toasty]

Re: Panasonic 27" Picture Problem

PlainBill >>Now of course the problem is finding the part. I don't think Radio Shack carries them.<<

lol

No but MCM, HBF, and Encompass do. $22-$28

[Krankshaft]

Re: Panasonic 27" Picture Problem

Well here is an update I turned up the screen and there is definately a full raster there.

I scoped out the tuner and there is a signal there I'll scope out the RGB input and output of the IC tonight and see what happens.

[i4004]

Re: Panasonic 27" Picture Problem

ntsc tellys don't have rgb-in anywhere...

rgb output will show signal when osd is on, and nothing when it's off....

yes, everything points to that ic.......you could check the quartz( pins 35..and 79-80 for the cou core....ok frequency?), but if osd is working chances are it's ok...

oh, btw. what's the tube(crt) in that one?
if it's same as in my 25" model(videocolor) it really can last a long time...

if it went bad (this tv), i would probably invest up to 300$ to fix it, as i know even at 13 age years it beats many things (new tvs) on the shrinking crt market of these days...
quite amazing.....panasonic was obviously over-engineering these things...fuckin excellent!