As I have previously mentioned, at times I was having what I suspect were signal integrity issues due to the messy wiring through the adapters, wires, breadboard etc running at 25mhz. I wanted to get a proper connection in place and know the signal quality is okay before investing time in trying to perfect the image on the display.
I am inexperienced with PCB design, and I was being impatient and wanted to get SOMETHING quickly so I was certainly sloppy with this layout and made a gamble on the colour wiring. I am fairly confident the MSB’s are correct, so at a minimum I can cut the other traces to at least use it to see if signal quality has improved and work on physical placement. The pin header is to power the led backlight and tft gate drivers (vcom/vgl/vgh) externally until I can verify what we need to put on the PCB itself. The boards are on the way and will be delivered in a couple days.
Some progress with connecting the AT050TN22 v1. As with previous tests, this only has the MSB for each colour connected. I will be sending out for a pcb prototype this week to test further. It looks quite good in person, and there is no flickering.
The style is very sloppy, this was put together in a rush very late to debug the chip. I may improve it later on as it did prove helpful. The assembly version written at https://garakutaen.sakura.ne.jp/ is excellent, however my assembly knowledge is not strong enough to make some of the changes I needed so it was easier to write in C.
The current values configured are for the AT050TN22 V.1 but are not confirmed to be correct.
You can use this program at your own risk. If you have any questions leave a comment.
UPDATE 2020/07/18: I have found some of the original OEM tools for debugging so the need for these custom programs for debugging may be no longer. I am going to maintain a page of all the tools I can find HERE.
So progress has been made with the electrical interface, there is still some work to do but I am at the stage of producing the PCB to connect the lines and generate the voltages. This brought the issue of, how much space do I have? and it turns out not really any.
The original Citizen is about 6mm thick except for the driver end where it requires about 9.5mm clearance due to capacitors. For this reason the rear body of the PC110 is expanded out to accomodate.
The AT050TN22 is also about 6mm thick, except where the driver board is attached which I believe is 6.2mm.
The AT050TN022 a useful feature of allowing us to select the horizontal and vertical scanning direction, Pin 39 Left/Right and Pin 40 Up/Down. This allows us to orientate the module in whatever way we need.
So my thought is to fold the ribbon cable so it comes out at the edge where we have additional clearance. the 30pin FPC connector would be on the bottom layer and the 50pin FPC on top layer. With some good planning the required components for generating the driver voltages and controlling backlight could also fit here, but if not there is lots of space on the other side where the old inveter was.
I am unsure if these folds in the ribbon cable may cause signal integrity issues with the 25MHz clock line zigzagging. Some testing will be needed.
With different folding we can position it to accommodate any layout restrictions on the PCB.
I ordered a VGA driver/controller board that is sold with/for the AT050TN22 v1 so I could verify how they are generating the timing and maybe learn an easier way to generate the needed voltages.
PIN37 (DCLK) is measured at 39.4042 MHz PIN9 (DE) is measured at 33.6341 KHz PIN8 (MODE) is pulled high PIN10 (VS) is is measured at 37.9157 KHz but ignored by display PIN11 (HS) is measured at 70 Hz but is ignored by display
Full length of DE pulse is around 16us (very lazy I eye-balled cursors)
I got the AT050TN22 V.1 in the mail finally from Aliexpress. I wanted to do some testing straight away so I quickly put together an adapter board for the 30pin to 50pin. I only connected the MSB for the colours as my main immediate concern is timing.
Downside of this unit vs the WVGA unit is we need to provide the voltages to drive the tft externally VCOM, VGH(+15V),VHL(-10V),AVDD, etc. This will need to be integrated into the adapter board, along with the +10V for the backlight which ideally will be powered and controlled by the inverter supply to maintain Fn- control of the brightness/contrast (vcom a/c)
I am currently playing with a TI TPS65100 for voltages, however most likely will implement something similar using passives if I can learn enough to cobble together something.
For timing in my initial tests I seemed to need to meet a minimum pixel clock of 25MHz to get an image but this was very preliminary. I also experimented with DE modem vs HV mode. It is not the easiest as we only have access to the pins from the CT65535 that were brought out for the original CSTN display.
For my initial attempt, I have used the WVGA (800×480) screen taken out of DTN-X680 GPS that I purchased online. Following instructions from https://garakutaen.sakura.ne.jp/index.html I created an adapter to connect the 30pin flat flex of the PC110 to the 40pin flat flex of the X680 display. I then used the CT65535 program from above to update the registers to switch over to the LCD. Generally it works, however I did not spend too much time on this yet as I want to more closely explore a closer matched screen I found (AT050TN22V1). There is a flickering which is not acceptable, I believe this is strictly related to the parameters used for timing / signal output on the ct65535 and not the quality of my wiring and could eventually be corrected. My main issue with this screen is the fact is the wrong aspect ratio and cannot take up the full display window.
The following is a gallery is my various attempts and failures:
I spent some time removing top layer however the second layer would not come off together so I had to spend time carefully scrapping it away.
After I had removed enough I powered the screen up and used a polarizing lense to look for any contents. I was unable to see anything and I noticed some cracks, presumably I caused this while attempting to remove the layers. In any case I called this a failure and ended it here.
I have several more of the failed screens, at a later date I may attempt again carefully removing the “rotten” layers and applying a new polorizing film. Although the tft upgrades are nice, I would like to one day have a working unit with the origional display.
I’ve searched high and low, and there does not seem to be a drop-in compatible replacement module. There are some sites that list stock for the citizen origional module, however when I contact them to ask if it is “new old stock” i.e. they have been on a box and likely also failed, they tell me they no longer have it.
So it seems, replacement route involves installing a different display (TFT) along with an adapter. I will explore this route in other posts.
Here is a look inside the dock / port replicator. Just looking around to see what is in there. As expected nothing too interesting.
The one thing I was interested to see/confirm was what the pin with the repair jumper wire connected to. It was pin#13 on J4 inside of the dock which I believe is considered pin88 on the overall connector. It connects GND, and jumps over to D2 dual diode package.