11AK45, strange CUT-OFF issue

[3CX15000A7]

I was given a 4:3 JVC with a 11AK45A chassis (Vestel) recently with a strange fault:

First thing I noticed (on all sources including RGB) is that there's something wrong with the black level: shadows details are crushed and turning op the brightness will make the blacks grey.

Further investigation tells that the set is constantly adjusting the brightness by it's own, in "digital" steps: If I switch from a bright testcard to black, the grey will darken in "digital" steps. From dark to testcard, the picture brightens in digital steps. But the brightness seems never to be right (by a large margin)

Seems to be a problem with the automatic cuf-off, because the behavior only appears in 4:3 mode. Switching to 16:9 mode, the automatic brightness adjustment stops, but also the measure lines normally seen aren't present.

Switching the set from off to on in 16:9 mode will give a picture with wrong colors (very blue), when I switch to 4:3, the colors will correct to pretty normal in digital steps.

That the picture is blue while turning on doesn't surprise me, the blue gun is stronger than the red and green (measureing 0,9mA for red and green, 1,1 for blue) using a CRT tester. It's a Thomson A66EHJ13X01 tube. It measures not the best anymore, but there's plenty of light and OK focus in real life.

I am doubting if it is a malfunction becasue the effect seems to be digital. I now that the 11AK45 has the reputation to be terrible, but I can't think this is designed by purpuse. Why would you destroy one of the best CRT aspects, deep blacks with good shadow detail?

Going throught the service menu and adjusting the G2 doesn't fix it . .

Is there someone that has experience with this chassis and can tell me if this is normal?

[Red to black]

I repaired lots of these sets about ten years ago while they were still current models.
I cannot say that I came across your symptoms back then.
This is now though and it maybe that the tube (CRT) is a bit flat and the AKB (Auto greyscale) system can no longer cope with being outside of its parameters for the circuit.
The RGB driver chip (IC) on the tube base wasn't the most reliable either, might be worth changing, also check any hi value resistors here too.
I am quite surprised any are still working to be honest.

[3CX15000A7]

Here in the Netherlands those sets are verry common, they pop up at least a few times a month on dutch bidding platforms.

From the inside it looks it had a hard life, it's extreme dusty.

Following the schematic it has a tda6109 AMP. A very familar one I think, see these a lot in last gen CRTs. Will follow the beam info line and check the resistors.

about the tube: I have a müter bmr95. All the guns are far in the "good" zone (with blue .2mA better than red/green at 0.9mA), but the life test says it doesnt have long anymore. Can look if this set also has a resistor/coil to boost the heater to see the results.

could also regenerate it, but I don't know if Thomson tubes respond good to it? Recently I succesfull regenerate a philips EAK from a cp110 that was really dull, the result was spectacular.

[Red to black]

They were very common here in the UK too back in the day.
They suffered badly from eeprom corruption too, if you think this might be the problem ?
I will have the original JVC eeprom dump copied from an original brand new JVC default chip, I also kept a copy of one after they were set up geometry wise (UK sound standard of course) if you have a spare chip and the means to write to it. I could zip it up and post it here if required ?, I think I stored them as either bin or hex files

[3CX15000A7]

What were the symtoms of a EEPROM failure? There aren't memory problems on this particular set. But the fault looks very digital because when the brightness changes its in steps.

I think a spare chip wouldnt be too hard to get. Come back to it next week when I go further on the set

[Red to black]

All sorts of problems could be caused by the eeprom, anything you care to mention, they could get stuck in stby, geometry problems, sound problems, anything and everything really.

The eeprom on these weren't just used for storing the channels, all of the service mode parameters and option settings for the set were stored in it too.

[Welsh Anorak]

I'd second EEPROM trouble. You could set the geometry up for the various aspect ratios to find the picture would vanish on 4:3, or at least pulsate which could be what yours is doing.
Unfortunately I don't have the sheets any more where I wrote down all the parameters from a good set for various tubes.

[ben]

Another vote for the EEPROM. In my limited experience of these any 'weird' faults could be solved by replacing it and resetting the relevant parameters.

There was one really nasty corruption which I think led the line drive to go way out of spec and cause a trail of destruction in the line output stage. As has been said, I am surprised any are still around these days!

[Red to black]

Hi ben, I have actually had faulty eeproms neck the tube on these before, what seemed to happen is that the DC coupled frame chip got either 'bottomed' or 'topped' out passing DC of one polarity or other through the scan coils causing them to overheat and necking the glass! as well as usually destroying the frame chip.

To the OP, unfortunately you cannot just fit a blank memory chip of the same type number, or even one from a different brand of 11Ak45, or the same chip from a different make of set, if it was a JVC version then you needed a JVC default eeprom, likewise for the Hitachi, Toshiba, Sharp and Bush versions.
Now buying the eeproms from the manufacturer pre-programmed with default values was expensive!, about 40 times more expensive than a blank chip cost! and you still needed to fully align the set geometry wise in all modes! as well as greyscale plus alter any option codes for features.
I only ever bought each type once, as I had the means to copy,read and write to and from these chips with an eeprom prgrammer, this meant I could save a working copy and buy cheap blank chips in future.
On the JVC version at least I saved a copy of the default one plus a copy of one that had been set up afterwards, which would only require minor adjustments on other sets of the same make and type compared to the default one, thus saving me much time.
I probably did the same for the other makes too.

The chips for these sets are pre-programmed, both with a header address file (so the sets micro can read from it) and default working parameters for each manufacturer, there are quite large discrepancies in the data supplied on them between manufactures brands.

[FIXITNOW]

I have a few EEprom files as well i guess we will need the full model number. and with luck one off us may have the file for this set which will at least get you started

[3CX15000A7]

The full model number is: AV-28KT1SUF with a Thomson A66EHJ13X01 tube. Chassis full name is 11AK45 A. It's a 4:3 set. I can note the geometry settings from the present chip.

I have to admit, I had to (re)do some geometry settings. The 16:9 mode was badly set up, with much too much blanking and some other misalignments. Maybe also caused by the EEPROM.

I ordered some EEPROM chips. I think I know someone with a programmer.

Does someone know what caused the common corruptions? A badly regulated PSU?

Thanks for the help so far

[FIXITNOW]

its here on the web as a bin file
https://elektrotanya.com/jvc_av28kt1.../download.html

also added here

[3CX15000A7]

Thanks!

Is the 11AK45B5 file compatible with a 11AK45A? My set is the A variant.

[Welsh Anorak]

No idea why they failed - they just did. Never had one fail on an AK49.
You'll need the list of values for the new EEPROM - and a spare afternoon! Even for the correct chassis and CRT they were still wildly out. Be prepared to compromise.
Had several kill the CRT, but always Samsung tubes.

[G6ONEDave]

The eeprom and cpu type chips failed in a lot of different tv sets. At least one manufacturer used to supply a repair kit with the replacement chips and a tin plate shield plate, sometimes also included the odd resistor and capacitor. The theory was that the chip/s had become faulty due to static charge from the crt. So the then remedy was to fit the tin shield over the top of the chip/s and connect the shield to chassis 0v. I prove that the diagnosis was correct, but I never had a repaired/modified tv set return for the same issue.

[FIXITNOW]

Originally Posted by 3CX15000A7

Thanks!

Is the 11AK45B5 file compatible with a 11AK45A? My set is the A variant.

according to web should be close but will need tweaking

fit a socket in board use old one in service mode for settings
then new file and tweak as required

once done read out so you have a back up for next time
You can get cheap programmer for 24c chips off ebay etc

[Welsh Anorak]

I remember with these you needed to switch to 4:3 to check the EEPROM. If the picture disappeared you needed to switch off quickly as the line stage would self-destruct - or worse!
I think the TV referred to in post #15 was the Philips G90 series. The shield fitted over the micro and the EEPROM and was earthed with the small wire that was supplied fitted to it. Later sets such as the GR1AX had one fitted as standard. No SCART on these, but that's another thread's topic at the moment..

[AC/HL]

Sounds like LCD arrived none too soon.

[Red to black]

Just as well FIN found the correct Bin file on ET, as when I looked at the JVC ones I had saved they were for the more common (in the UK at least) wide screen 16:9 versions.

[3CX15000A7]

Originally Posted by Welsh Anorak

I remember with these you needed to switch to 4:3 to check the EEPROM. If the picture disappeared you needed to switch off quickly as the line stage would self-destruct - or worse!
I think the TV referred to in post #15 was the Philips G90 series. The shield fitted over the micro and the EEPROM and was earthed with the small wire that was supplied fitted to it. Later sets such as the GR1AX had one fitted as standard. No SCART on these, but that's another thread's topic at the moment..

What exactly do you mean by "check the EEPROM" ?

When I go through the service menu, staying on some widescreen settings makes the picture dissapear. Is this the point I have the risk to self destruct?

@AC/HL
LCD's that took over when CRT went out were picture wise the most terrible sets . . I remember that in a few years all CRT's were gone. My first LCD (Samsung around 2010) was the worst set ever. When I moved my head, the corners turned grey. Black was grey overall, red was orange, light output was avarage, motion was blurry, a very agressive AR coating makes everything dull and with the then available SD signal everything looks very jagged and digital processed. Those Vestel sets were really high-end compared to LCD .

@Red_To_Black
Netherlands was very late with adopting 16:9, I think it was arround 2008 most broadcast were. For years, the testcard was most broadcasted in widescreen