MP3Car.com - View Single Post - Lilliput FA841, 14 Pin Centronics pinout (verify plz) and several problems

h3rk · 04-13-2008, 04:05 PM

Here's my troubleshooting progress so far.

I've checked continuity across that FFC connector, it's definately a problem, it needs pressure to keep reliable continuity across it but I don't think it's my only problem. (As of yet I don't exactly know what my problem is... maybe spending so much time fussing with this lilliput board

.)

I've found the parts of the circuit that comprise touch controller: (the bit in the OP about having an 'upgraded controller' was a bit off, but that's what I understood from my correspondence with MCT. Monitors and LCD's have never been something I've spent much time digging into, so I'm learning much as I go).

This is a chip by Cypress, an enCoRe™ USB Combination Low-Speed USB and PS/2 Peripheral Controller. (datasheet)

I traced the centronics female connector pins 6 and 14 to this point before, looked up the chip, and didn't go any further it seemed right to me, but since I can't get things to work still, I go deeper. Again I've verified continuity from the centronics female connector pins 6 and 14 to pins 15 and 16 shown just above. Vcc is supplied onboard through the filtered regulated circuit which employs a LM7805.

At that circuit, I found 4.95Vdc, but closer to the USB circuit (pin 14) I'ts only 4.36Vdc, I was expecting less of a voltage drop. Both pins 9 and 10 are to ground as it says they should be in the data sheet. In fact if you look at this section of the board, and then look at TVI's USB 4-wire controller, they look very similar.

I am also figuring that the output of this circuit has to be functioning at least well enough to identify itself as a universal touchscreen controller in my device managers.

So now I move on to the rest of the circuit, now I haven't traced it all out yet, but it seems to me that the small chip nearest (lower corner) the CY7C63743 is part of an external clock circuit with the 6Mhz crystal oscillator. Please feel free to chime in and upgrade me though.

What's left is the input circuit: P0[7:0] and P1[7:0] and their connections.

On one side there are a few pins tied 3 202 smd resistors in parallel with eachother and seperated from gnd by that c104 cap to ground. I'm not sure if that's right (haven't probed too deep), I really have no idea how they coded the chip, and what they would use that for.

But on the other side of the chip there are several (4) more inputs from another chip whos markings I do not recognize, which I expect to be some A/D converting type of thing. It gets it's inputs from those items marked MC, I'm assuming some sort of transistor switches that fire when you touch the screen. ? (maybe memory cell? locking in the voltage from the last press until it can be looked at?)

When I take voltage readings on each of these pins, the top (in the picture above) is 4.36V, the bottom is 0V and the other 2 are... mostly they read around 0.020-0.050Vdc. I'm guessing they are the sensing pins. Which is like what little I know of how these 4wire sensors work.

No matter how well I seat and compress the flimsy little ffc connector, nothing responds. I did take continutity across it as previously stated, and I get 0 ohms *4. I did see a bit of voltage at one of the middle 2 pins once, but I can't really reproduce it.

What kind of voltage should I see?

As I understand it, the sensing wires pass along a voltage that drops fairly linearly across each dimension. I can't see that.

I secured the monitor and removed the touchscreen connector from the controller board. I checked continutity between all pins, and there was no continutity from the top pin or from the bottom pin to any of the other pins pressing the screen or not. But the two center pins had continuity to eachother when (only) I press the touchscreen. And this is through the FFC connector. lower left is like 250 ohms and upper right is 1200 ohms. Resistance varies directly with distance from the lower left.

I wasn't super sure what I expected to see, but I wasn't really expecting it to go like that.

Does that look right?

I also tested directly to the FFC ribbon traces, and got the same thing.

So there, I kind of quickly scanned through through the whole setup, and I'll have a picture up of the FFC connector and how it's connected soon, I forgot to take one of that. I'm also going to try to read up more on resistive 4 wire touchscreens and how the touchscreens 4 wires should be. What I saw really doesn't seem right to me. More on that later, I guess.

So...what should I do?

I'm thinking about just getting a whole different controller~$42, plug it into USB maybe get another FFC connector from digikey (hopefully one that's less flimsy and easily seperated) and a small PCB to solder to. if that doesn't work, maybe a new touchscreen (maybe one of the ones at TVI as well, I'm sure they work together) ~$56 for 8.4".

Then again, that NEC does look good (I just found the NEC 8.4 transflective thread today

.

oh yeah I almost forgot....

04-13-2008, 04:05 PM	#2
h3rk FLAC Join Date: Oct 2006 Location: Las Vegas Posts: 1,286	Here's my troubleshooting progress so far. I've checked continuity across that FFC connector, it's definately a problem, it needs pressure to keep reliable continuity across it but I don't think it's my only problem. (As of yet I don't exactly know what my problem is... maybe spending so much time fussing with this lilliput board.) I've found the parts of the circuit that comprise touch controller: (the bit in the OP about having an 'upgraded controller' was a bit off, but that's what I understood from my correspondence with MCT. Monitors and LCD's have never been something I've spent much time digging into, so I'm learning much as I go). This is a chip by Cypress, an enCoRe™ USB Combination Low-Speed USB and PS/2 Peripheral Controller. (datasheet) I traced the centronics female connector pins 6 and 14 to this point before, looked up the chip, and didn't go any further it seemed right to me, but since I can't get things to work still, I go deeper. Again I've verified continuity from the centronics female connector pins 6 and 14 to pins 15 and 16 shown just above. Vcc is supplied onboard through the filtered regulated circuit which employs a LM7805. At that circuit, I found 4.95Vdc, but closer to the USB circuit (pin 14) I'ts only 4.36Vdc, I was expecting less of a voltage drop. Both pins 9 and 10 are to ground as it says they should be in the data sheet. In fact if you look at this section of the board, and then look at TVI's USB 4-wire controller, they look very similar. I am also figuring that the output of this circuit has to be functioning at least well enough to identify itself as a universal touchscreen controller in my device managers. So now I move on to the rest of the circuit, now I haven't traced it all out yet, but it seems to me that the small chip nearest (lower corner) the CY7C63743 is part of an external clock circuit with the 6Mhz crystal oscillator. Please feel free to chime in and upgrade me though. What's left is the input circuit: P0[7:0] and P1[7:0] and their connections. On one side there are a few pins tied 3 202 smd resistors in parallel with eachother and seperated from gnd by that c104 cap to ground. I'm not sure if that's right (haven't probed too deep), I really have no idea how they coded the chip, and what they would use that for. But on the other side of the chip there are several (4) more inputs from another chip whos markings I do not recognize, which I expect to be some A/D converting type of thing. It gets it's inputs from those items marked MC, I'm assuming some sort of transistor switches that fire when you touch the screen. ? (maybe memory cell? locking in the voltage from the last press until it can be looked at?) When I take voltage readings on each of these pins, the top (in the picture above) is 4.36V, the bottom is 0V and the other 2 are... mostly they read around 0.020-0.050Vdc. I'm guessing they are the sensing pins. Which is like what little I know of how these 4wire sensors work. No matter how well I seat and compress the flimsy little ffc connector, nothing responds. I did take continutity across it as previously stated, and I get 0 ohms *4. I did see a bit of voltage at one of the middle 2 pins once, but I can't really reproduce it. What kind of voltage should I see? As I understand it, the sensing wires pass along a voltage that drops fairly linearly across each dimension. I can't see that. I secured the monitor and removed the touchscreen connector from the controller board. I checked continutity between all pins, and there was no continutity from the top pin or from the bottom pin to any of the other pins pressing the screen or not. But the two center pins had continuity to eachother when (only) I press the touchscreen. And this is through the FFC connector. lower left is like 250 ohms and upper right is 1200 ohms. Resistance varies directly with distance from the lower left. I wasn't super sure what I expected to see, but I wasn't really expecting it to go like that. Does that look right? I also tested directly to the FFC ribbon traces, and got the same thing. So there, I kind of quickly scanned through through the whole setup, and I'll have a picture up of the FFC connector and how it's connected soon, I forgot to take one of that. I'm also going to try to read up more on resistive 4 wire touchscreens and how the touchscreens 4 wires should be. What I saw really doesn't seem right to me. More on that later, I guess. So...what should I do? I'm thinking about just getting a whole different controller~$42, plug it into USB maybe get another FFC connector from digikey (hopefully one that's less flimsy and easily seperated) and a small PCB to solder to. if that doesn't work, maybe a new touchscreen (maybe one of the ones at TVI as well, I'm sure they work together) ~$56 for 8.4". Then again, that NEC does look good (I just found the NEC 8.4 transflective thread today. oh yeah I almost forgot....