Help! : CXA2120Q or Scrap Mitsubishi VZ5 to VZ8 signal boards!

Jeff, what makes you think this chip is bad. I have rebuilt many of these boards and never had one bad. The problems is almost always caps or damage from coolant.

Leonard

Original problem was the typical dark/poor picture caused by low 9V from Ic2p01.

Was reading 7V on the output , changed the IC and the caps ( All the caps by the regulators) and problem was solved.

Brought back lightbox to customers house , picture was quite a bit larger than it should be vertically and horizontally.

VSIZ adjusted height OK , but HWID had no effect.

Brought box back to shop , removing the focus lens & looking into the crt lens you can see where the normal phosphor wear and tear was on the face of the CRT and the set was now scanning beyond that Vertically and Horizontally.

Horizontal pulse width is at 14uS of so and does not vary at all when the HWID is adjusted. Scoping the output of the VCJ chip shows no change in the time of the drive signal

The fact that the Vertical is too big is a sign that is a Hdrive problem as it drive the High Voltage a bit higher also which is increasing overall raster size.

Sounds reasonable? Or am looking at this in the wrong way?

This set is dry as a bone...no coolant here!

========================== Jeff Stielau Shoreline Electronics Repair

Exactly which set and chassis is this?

Leonard

VS-60707 VZ8 chassis

================================= Jeff Stielau Shoreline Electronics Repair

Do you have the disc on this one?

Leonard Caillouet Electronics World

By disc , do you mean service manual? If so , yes. Training and Service manuals.

Pretty straight ahead design.....the one H-drive drives the discrete HV & H-sweep circuits.

As it varies the pulse width of the H-drive , HV and H-Sweep will increase or decrease.

If the problem was in just the H-Sweep circuit , I wouldn't have the oversize vertical raster....no? Keepin mind I can adjust Vertical size.....just cant adjust H-SIZE.

Any thoughts on what else might cause this?

========================== Jeff Stielau Shoreline Electronics Repair

Good old Murphy (for real, Elden Murphy, Murphy's TV) always said "the TV has one problem" In those days he was usually right, but now we know better.

Still, when you have a situation such as this, it is still most logical to look for ONE cause for the set of symptoms. In that light, yup, you got a "fun" one as BillJr would put it.

I know this is a different set, but it is reminiscent of the Sonys on which you can't adjust the Hphase. Apparently there are two feedback/references and when they are too different, the VCJ gives up on the parameter. On that set the problem was a small cap between the HOT collector and the VCJ, remember ?

Now comes this fact : That is a Sony IC.

And : They program some interaction between geometry functions. That is many set use HV level and load, as well as H and V feedback to dynamically correct the geometry under vastly varying loads. Even CRT beam density is figured in. (yes, if you regulate the HV absolutely rock solid, the raster will shrink at higher brightness ! )

So ; I would scrutinize any and all components that provide feedback from horizontal deflection to the VCJ. It could be completely gone. In that case the Hphase is probably off as well, but when it's overscanning you might not be able to tell.

Going on to a bit of supposition here, the convergence is easily able to correct the pincushion on the sides. The reason that there even is a pincushion circuit in the H deflection circuit is so they can apply this dynamic correction to keep the geometry rock solid while displaying i.e. an explosion in the dark.

Look for small lytics, and high value resistors that feed an actual sample of H sweep to the jungle. I'll lay 50/50 odds that when you find the bad component it will be wet. All it takes is a drop of coolant. I got fooled the other day because I hadn't noticed coolant on the board, and I DO look. I literally didn't know it until it sizzled from the heat of my soldering iron.

JURB

I will double check this area again. I have a used CXA2120Q on it's way to me also.

Although this is the first time I've seen this part fail, according to Mike at Prelco Parts , they are indeed a high failure part according to the fact that PTS has on going open purchase orders for as many of these as they can lay their hands on.

I even called PTS to get a price for a board or rebuild and they said they cannot fix these do to parts NLA

I mentioned to him that google searching for these reveals many suppliers overseas that claim to have thousands in stock. He states that most of these companies that claim to have them are relabeled junk parts

Anywho.......when me spare CXA arrives , I will put chassis back on the bench and double check feedback loops and drip scenarios one more time before I swap the flat packs.

Stay tuned!

-- ========================== Jeff Stielau Shoreline Electronics Repair