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Toshiba PD1843 15khz dim image/low brightness

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chriszhxi

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31khz/24khz brightness is fine, but 15khz brightness is too low, adjustment wouldn't help, any suggestion?
 
Turn up the voltage from the flyback and then adjust 31khz / 24khz brightness down from the remote?
 
Could this be related to a mismatch of the input signal (VGA/jamma) and which header on the chassis is being used as well?
 
nem said:
Turn up the voltage from the flyback and then adjust 31khz / 24khz brightness down from the remote?
Click to expand...
The brightness difference is too big, if I bring up brightness, the black part would be too bright, there got be something wrong with the chassis.
 
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tiff_lee said:
Could this be related to a mismatch of the input signal (VGA/jamma) and which header on the chassis is being used as well?
Click to expand...
I'm using VGA input and the black input connector on the chassis which is amplified, maybe it's the amp got problem handling 15khz signal but I'm not sure.
 
The MCU on the Toshiba PF is responsible for controlling the I2C bus and changing the settings in the
  • Video Amp-LM1269NA
  • Deflection IC - NEC C1888FCT (NEC uPC 1888 )
All the settings in the OSD are just the MCU configuring either the video amp IC or the Deflection IC via I2C. The MCU saves the settings in a serial EPROM, that is also on the I2C bus. I have seen several cases where the serial EPROM gets corrupted and the MCU is unable to change the setting. Often times its the Brightness or Contrast that gets corrupt and set to a really low value, resulting in a very dim picture that is unable to be corrected.

What you can do is take the serial EPROM off the I2C bus and the MCU will load default settings. You can then put the serial EPROM back on the I2C bus, and go through all the settings in the OSD. By changing each setting, the MCU will be writing out the new value to the EEPROM. You can esentially re-write all the saved settings to the serial EPROM and overwrite any corrupt values.

In the photo below I have replaced the wire jump link with a pin header. I have no jumper on the pin header, so the serial EPROM is removed from the I2C bus.


IMG_2367.jpg



With the monitor still powered on, re-install the jumper. This will put the serial EPROM back on the I2C bus. Once you re-install the jumper, go through all the OSD settings and change each value by 1, you can change it back to the original setting, but by at least toggling the value, the MCU will write it to the serial EPROM and should fix the corruption.


IMG_2366.jpg




I have seen about a dozen Toshiba chassis where the contrast value gets corrupted and once its corrupted you cant change it with the MCU. The corrupt contrast value makes the monitor super dim and the OSD is unable to change the value. The steps I outlined above have seemed to fix the corruption in the chassis that I have come across.
 
dewmansnk said:
The MCU on the Toshiba PF is responsible for controlling the I2C bus and changing the settings in the
  • Video Amp-LM1269NA
  • Deflection IC - NEC C1888FCT (NEC uPC 1888 )
All the settings in the OSD are just the MCU configuring either the video amp IC or the Deflection IC via I2C. The MCU saves the settings in a serial EPROM, that is also on the I2C bus. I have seen several cases where the serial EPROM gets corrupted and the MCU is unable to change the setting. Often times its the Brightness or Contrast that gets corrupt and set to a really low value, resulting in a very dim picture that is unable to be corrected.

What you can do is take the serial EPROM off the I2C bus and the MCU will load default settings. You can then put the serial EPROM back on the I2C bus, and go through all the settings in the OSD. By changing each setting, the MCU will be writing out the new value to the EEPROM. You can esentially re-write all the saved settings to the serial EPROM and overwrite any corrupt values.

In the photo below I have replaced the wire jump link with a pin header. I have no jumper on the pin header, so the serial EPROM is removed from the I2C bus.


IMG_2367.jpg



With the monitor still powered on, re-install the jumper. This will put the serial EPROM back on the I2C bus. Once you re-install the jumper, go through all the OSD settings and change each value by 1, you can change it back to the original setting, but by at least toggling the value, the MCU will write it to the serial EPROM and should fix the corruption.


IMG_2366.jpg




I have seen about a dozen Toshiba chassis where the contrast value gets corrupted and once its corrupted you cant change it with the MCU. The corrupt contrast value makes the monitor super dim and the OSD is unable to change the value. The steps I outlined above have seemed to fix the corruption in the chassis that I have come across.
Click to expand...

Thanks for the info. In my case, I can set both brightness and contrast and they are changed correspondingly on screen, chassis will also remember them, it's just the brightness or contrast is low even set at max value, and only at 15khz.

I don't have parts could be used as a jumper right now, do I need to put the EPROM back while chassis is on or I can do it when chassis is off? what about just replace the EPROM?
 
It seemed like the EEPROM was fine in the instances I ran into, just the MCU writes out garbage data for some reason and corrupts the EEPROM. If you can adjust the contrast/brightness with the remote board, then I don't think you are running into the EEPROM corruption. In the cases I had seen, the brightness/contrast was stuck and the OSD was reporting it at 100 and it was not changeable with the remote board. Also, the corruption seemed to only affect a single scan rate - if 15Khz was affected, usually 31Khz was just fine. This make sense since the MCU stores unique values for each scan rate (15, 24 ,31)

If the EEPROM has corrupt values, you need to put it back in circuit while the chassis is on. If you put the EEPROM back on the I2C bus with the chassis off, then the MCU will load the corrupt value when it powers on, and it will be in the failed state. Removing the EEPROM from the I2C bus before power on allows the MCU to load defaults from its own internal memory, then putting the EEPROM back on the I2C bus while the chassis is on allows the MCU to write out good values to the EEPROM.

Also, the MCU itself seems to suffer from its own internal memory corruption. Removing the EEPROM from the I2C bus and powering on the chassis - I had seen cases where the R G B gain and cutoff values were different, where I would expect them to be the same.
 
dewmansnk said:
It seemed like the EEPROM was fine in the instances I ran into, just the MCU writes out garbage data for some reason and corrupts the EEPROM. If you can adjust the contrast/brightness with the remote board, then I don't think you are running into the EEPROM corruption. In the cases I had seen, the brightness/contrast was stuck and the OSD was reporting it at 100 and it was not changeable with the remote board. Also, the corruption seemed to only affect a single scan rate - if 15Khz was affected, usually 31Khz was just fine. This make sense since the MCU stores unique values for each scan rate (15, 24 ,31)

If the EEPROM has corrupt values, you need to put it back in circuit while the chassis is on. If you put the EEPROM back on the I2C bus with the chassis off, then the MCU will load the corrupt value when it powers on, and it will be in the failed state. Removing the EEPROM from the I2C bus before power on allows the MCU to load defaults from its own internal memory, then putting the EEPROM back on the I2C bus while the chassis is on allows the MCU to write out good values to the EEPROM.

Also, the MCU itself seems to suffer from its own internal memory corruption. Removing the EEPROM from the I2C bus and powering on the chassis - I had seen cases where the R G B gain and cutoff values were different, where I would expect them to be the same.
Click to expand...
Got it fixed!

First I replaced the L01A EEPROM (got from another spare PD1843), 15k was still dim and even darker than before, but I found out that contrast was locked at 100 this time, can't adjust it.

So I managed to make a temporary jumper from what I got, followed your instruction, turned on without the jumper connected, and 15k is back to normal!

I put the jumper on, made changes through all adjustments, rebooted with jumper on, it's still good, problem solved.

a.jpg

Looks like it's still related to EEPROM and MCU, it's kinda weird I could adjust contrast at first place, likely it was not corrupted, maybe the EEPROM stored like offset data in it?

Anyway thanks for help!
 
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Glad that fixed the issue. Looks like you ran into a different failure mode the first time around. The contrast being locked at 100 is the one I am used to seeing. I had been meaning to update my Tosh PF thread with this EEPROM fix, guess I need to get around to doing that.
 
Bumping this up, I have a PB9929 which is displaying the OSD but no video. I've confirmed with my scope that a video signal is going into the M52337SP input pins, and I've replaced that IC with a spare and had no change, so the amp itself is presumably fine. The OSD settings aren't making a difference at all, so I'm guessing the EEPROM is corrupt. The PB9929 design is different from the PD1843, but I did try disconnecting the jumper connected to the EEPROM's SDA pin, reconnecting the jumper, and changing the settings with no success. I would assume lifting SDA would remove it, but maybe I'm wrong.

@dewmansnk any ideas before I cut all the traces and wire the sub contrast and sub brightness pins up to pots? lol
 
trashedcabs said:
Bumping this up, I have a PB9929 which is displaying the OSD but no video. I've confirmed with my scope that a video signal is going into the M52337SP input pins, and I've replaced that IC with a spare and had no change, so the amp itself is presumably fine. The OSD settings aren't making a difference at all, so I'm guessing the EEPROM is corrupt. The PB9929 design is different from the PD1843, but I did try disconnecting the jumper connected to the EEPROM's SDA pin, reconnecting the jumper, and changing the settings with no success. I would assume lifting SDA would remove it, but maybe I'm wrong.

@dewmansnk any ideas before I cut all the traces and wire the sub contrast and sub brightness pins up to pots? lol
Click to expand...
To follow up on this, the cause of the fault was a bad MCU. I swapped one from a parts chassis and everything works again. Hopefully one day we can get a dump of the ROM so we can program new ones!
 
trashedcabs said:
To follow up on this, the cause of the fault was a bad MCU. I swapped one from a parts chassis and everything works again. Hopefully one day we can get a dump of the ROM so we can program new ones!
Click to expand...
MCU ????
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OK I'm going outside 🐌🐌🐌🐌😋😅
 
Mentioned this in a DM earlier but the PE0493 I was working on today had stuck contrast on all resolutions. Removing the eeprom from the bus reset all settings except contrast which remained locked. I pulled the eeprom off the board and manually overwrote all bytes with a nice medium value of 80, and once installed back on the board my contrast control worked again. Not sure why the MCU was unable to write this to the eeprom but I guess this is a last ditch solution if removing it from the bus doesn't work!
 
Hi! trashedcabs :)

Hi could you make a diagram with photos of the procedure to follow ?

THANKS :thumbup:
 
chacal231077 said:
Hi! trashedcabs :)

Hi could you make a diagram with photos of the procedure to follow ?

THANKS :thumbup:
Click to expand...

It's pretty much exactly as it sounds. Desolder the EEPROM, put it in your chip programmer, overwrite all bytes with a value of 80, flash it, solder it back on. It's a surface mount chip on the back of the board with the model L01A.
 
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