Lynx 2 blank screen

[Jago2k]

hi guys

Hoping to pick your collective brains

 

mate of mine has given me lynx 2, very happy as ive been wanting one for ages.

 

It didnt power on, but searched on here and found the wire between the battery and headphone trick, I have done this and now it powers on battery power.

 

All i get is a blank screen now though. Ive tried multiple games and its the same with all of them. the brightness wheel does nothing and there is now sound.

 

I was hoping someone here may be able to point me in the direction of what to look at next.

 

Thanks for looking

[SignGuy81]

The next step I would do is test for +5V at TP15

[bdoi]

Is there now sound? Or no sound?

Because if you don't hear any sound there is probably a fried chip mickey or suzy and consequently a dead lynx

[Jago2k]

Is there now sound? Or no sound?

Because if you don't hear any sound there is probably a fried chip mickey or suzy and consequently a dead lynx

Yep no sound at all.

Sounds like I have a dead lynx. I will test it at the first fine gentleman said.

 

Cheers for your advice will have to keep an eye out for a replacement lynx

[+Stephen Moss]

It didnt power on, but searched on here and found the wire between the battery and headphone trick, I have done this and now it powers on battery power.

 

I really wish people would stop perpetuating this horrid hack as a solution, while it will permit your lynx to turn on, long term it is likely to do more harm than good…

 

The incoming 9V supply from the external power unit/batteries is the common supply rail that runs throughout all the Lynx’s circuits. The Zenner diode and associated resistor create a floating single point ground reference “0V/Gnd” relative to the +9V supply for those parts of the circuit shown as running from 5V, but in reality that “0V/Gnd” is sitting at +4V relative to the actual 0V/Gnd provided by the external power supply/batteries. The remaining 4V is then dropped across Q12.

 

I appreciate that may be a little difficult to follow so hopefully the diagram below will help, voltages referenced to the power source are on the left, those referenced to the majority of the Lynx's circuits (some use +9V) are on the right.

 

+9V -------------------- +5V

¦

Zenner (4.3V, 1N5991B)

¦

+4V -------------------- Pseudo 0V (single point Ground reference for 5V parts of the design)

¦

FET (Q12, MTD3055E)

¦

0V -------------------- 0V (actual 0V/Gnd, from incoming Supply, used by the power on/off circuits)

 

Employing the horrid bodge of connecting the “headphone” ground to the power supply ground instead of fixing the real problem (probably a blown Q12), ties what should be a floating pseudo “ground” to the power source ground. As a result the Zenner cannot perform its intended function (and may well die trying). Consequently, I would expect to find all those circuits that should be running at 5V to now be running at 9V, potentially causing component failure due to excessive power dissipation as almost double the voltage = almost double the power dissipation.

[Pat Chapman]

On 3/22/2018 at 7:23 AM, bdoi said:

Is there now sound? Or no sound?

Because if you don't hear any sound there is probably a fried chip mickey or suzy and consequently a dead lynx

What if you can hear sound, but no display, backlight is on,, ? 

[+Stephen Moss]

16 hours ago, Pat Chapman said:

What if you can hear sound, but no display, backlight is on,, ? 

That would suggest that the problem is limited to the display, video creation getting eth video data to the screen as it suggest that Power, System clock and reading data from the cartridge are all OK.

 

Did you try measuring the voltage at TP12 as mentioned above, that is the primary voltage supplying the Display, secondary voltages are LDC_VDD at TP and LED_VSS at TP23, if any of those are not functioning you won't get any display (connect the COM lead of your multi-meter to the negative end of C41).

[Pat Chapman]

8 hours ago, Stephen Moss said:

That would suggest that the problem is limited to the display, video creation getting eth video data to the screen as it suggest that Power, System clock and reading data from the cartridge are all OK.

 

Did you try measuring the voltage at TP12 as mentioned above, that is the primary voltage supplying the Display, secondary voltages are LDC_VDD at TP and LED_VSS at TP23, if any of those are not functioning you won't get any display (connect the COM lead of your multi-meter to the negative end of C41).

I get anything from 5v to 10.7V at TP12 when I adjusy the brightness.

at TP23 i only get -1V

 

I have tested the screen in another Lynx MK2 and it works.. and also visa veresa board inside a case with a good screen..   

 

Speaker is faulty , but that can be common.. 

 

 

 

[oski_98]

On 12/15/2021 at 1:08 AM, Stephen Moss said:

That would suggest that the problem is limited to the display, video creation getting eth video data to the screen as it suggest that Power, System clock and reading data from the cartridge are all OK.

 

Did you try measuring the voltage at TP12 as mentioned above, that is the primary voltage supplying the Display, secondary voltages are LDC_VDD at TP and LED_VSS at TP23, if any of those are not functioning you won't get any display (connect the COM lead of your multi-meter to the negative end of C41).

@Stephen Moss, For a Lynx II, What should the voltages at "LCD VSS" TP23 and "LCD VDD" TP22 and "LCD TPR" TP27 be? I have a C104129-001 REV 2 board and when I probe these lines at the header I see:

• LCD VDD : 3.125 kHz square wave with min 4V and max 20V
• LCD TPR : 3.125 kHz square wave with min 4V and max 20V
• LCD VSS : 3.125 kHz square wave with min -11.5V and max 5V
• All the other pins are either held somewhere between 4.5 to 5 V or have logic waveforms on them in the 0 - 5V range.

Is this WAI? My best guess is that LCD VDD, TPR, and VSS form some kind of PWM control for the LCD brightness control? I ask because I recently revived this Lynx II to the point where I get audio from the device (see this thread). But when I plugged in the screen, it's backlit but there's no discernible images. It's just dark/blank (if I squint at it really hard I sometimes think I'm maybe seeing the title screen but that could just be my eyes playing tricks on me). I know the screen is good because I plugged it into another Lynx II, a Hayato Lynx II, and it works. I have an alternate theory that the screen I have is not compatible with the C104129-001 REV 2 Lynx II (which has a Mikey). When I got it someone had written "okay" on the back of it with a sharpie, so maybe I bought a botched repair job, but I can't find enough information online to confirm what LCDs are compatible with the C104129-001 REV 2 board.

[+Stephen Moss]

The following measurements were made with respect to the single point ground (taken from the negative terminal of C41)

DC voltage using a multi-meter:

Tp22 = 5.6V - 11V at min/max setting of the brightness control

Tp23 = -3.3V to -6V at min/max setting of the brightness control

Oscilloscope measurement, frequency varied slightly between 3.178KHz & 3.27KHz, as for voltage...

Tp22 range was approximately 10 to 18V p-p

Tp23 range was approximately 10 to 20v p-p

see attachments, x scale is 200uS/Division, order top to bottom is Tp22min, Tp22max, Tp23max, Tp23min.

 

[FlawleZ]

On 12/14/2021 at 10:02 AM, Pat Chapman said:

What if you can hear sound, but no display, backlight is on,, ? 

That's what mine does. Recorded a video of it:

 

[oski_98]

@Stephen Moss Many thanks, I really appreciate the data. Your measurements are consistent with mine. I see the same square waves, roughly the same frequency, and with the contrast turned way up, TP22 is -600mV at trough to 17.8V at crest, TP23 is -17.0V at trough to 800mV at crest.

 

At this point, I think I can rule out the LCD power circuit as the issue. I'll have to think about what to check next, but it's starting to look like I'll just have to try an LCD replacement.

[+Stephen Moss]

I am not really clear on how the Lynx moves data around, from the schematic it looks like Mikey/Hayato sets the cart ROM Address, the data is read into Suzy and then some how passed to RAM or Mikey/Hayato as applicable.

 

If that is the case then if you have what seems to be normal game sound that would suggest that at least that mechanisms is generally working and so with Mikey/Hayato setting the cart read address it must therefore be operating in at least some capacity.

Have you tried looking at the other signals to the LCD to see what is going on there, I am not sure exactly what they should be but if you are using a cart you can appear to start or that has an attract mode like Ms PACMAN then you would reasonable expect the signals (with the exception of the two 5V pins and possibly RESET, cannot be certain about RESET without the LCD datasheet) to change as the screen is updated so look for any that don't as they may at least give an indication as to whether or not video data is being sent to the LCD.

If you do try monitoring the other LCD pins with the LCD connected and find any that are not changing then recheck the with the LCD disconnected, if the result is different that could suggest an LCD fault is holding that signal.  

[oski_98]

I'm definitely seeing 5V logic waveforms or clock signals on the other pins. I don't have a logic analyzer, so I can't make much of sense of it, but nothing is at 0V except the grounds.

 

What might help is of anyone else with one of these rarer C104129-001 motherboards could share some pictures of their LCD screen so I could confirm whether someone swapped the original on my unit with one that's incompatible. Or maybe it would help to know what the differences are between the LCDs on the different revisions. In the meanwhile, I think what I'll do is compare the signals on a Lynx II Hayato unit. I'll post here if I discover anything interesting.

[oski_98]

So I have a theory as to what's going that might explain the blank screen behavior I'm seeing on my unit. The crux of this theory is that the BennVenn Rev6b screen requires attaching the RESET pin of their LCD to TP27 instead of the RESET at pin 21 of the LCD header for C104129-001 motherboards. The difference between these two, when probed with an oscilloscope, is that they are the inverse of each other. That is TP27 is a 60Hz square wave that pulses high from 0V to 5V and has a mean voltage of .05V, whereas pin 21 on the LCD header is a 60Hz square wave that pulses low from 5V to 0V and has a mean voltage of 4.7V. Put simply, and increasing the scale by 3600x, this is the difference between turning a light switch on/off quickly every minute (you're mostly in the dark) vs turning a light switch off/on quickly every minute (you're mostly in the light). I guess the point of both these signals is to clear the screen before drawing the image, that would make sense if we assumed the Lynx had a refresh rate of 60Hz.

 

I'm guessing that this might be a key difference between the LCDs for C104129-001 motherboards with Mikey chips and the later revisions with Hayato chips. And I think it's possible that if you put a Hayato Lynx II LCD display in a Mikey Lynx II motherboard, what would happen is that LCD would not work with that reset signal. If a Hayato compatible LCD resets by detecting a low to high edge, and shows a frame on the high to low edge, then I imagine an inverse signal would clear the screen and keep the screen clear for the majority of the time, show the image so quickly you couldn't possibly see it with the naked eye, then clear the screen right back again. You may be able to barely discern static elements of the display if you had amazing vision, but otherwise it would appear totally blank. This is what I think is going on with my unit at least, and at this point I'm just going to see what happens if I wire up the BennVenn LCD display since it's the path of least resistance. However, if I am right, and this is the only difference between a Hayato Lynx II display vs a Mikey Lynx II display, then it might be possible to work around these issues with a factory LCD by simply inverting PIN21, or in the case of a C104129-001 motherboard rewiring pin 21 on the LCD header to receive the signal from TP27 instead. I might actually try this, but not before I make sure the BennVenn LCD works to rule out other possible issues.

 

[+-^CrossBow^-]

3 hours ago, oski_98 said:

So I have a theory as to what's going that might explain the blank screen behavior I'm seeing on my unit. The crux of this theory is that the BennVenn Rev6b screen requires attaching the RESET pin of their LCD to TP27 instead of the RESET at pin 21 of the LCD header for C104129-001 motherboards. The difference between these two, when probed with an oscilloscope, is that they are the inverse of each other. That is TP27 is a 60Hz square wave that pulses high from 0V to 5V and has a mean voltage of .05V, whereas pin 21 on the LCD header is a 60Hz square wave that pulses low from 5V to 0V and has a mean voltage of 4.7V. Put simply, and increasing the scale by 3600x, this is the difference between turning a light switch on/off quickly every minute (you're mostly in the dark) vs turning a light switch off/on quickly every minute (you're mostly in the light). I guess the point of both these signals is to clear the screen before drawing the image, that would make sense if we assumed the Lynx had a refresh rate of 60Hz.

 

I'm guessing that this might be a key difference between the LCDs for C104129-001 motherboards with Mikey chips and the later revisions with Hayato chips. And I think it's possible that if you put a Hayato Lynx II LCD display in a Mikey Lynx II motherboard, what would happen is that LCD would not work with that reset signal. If a Hayato compatible LCD resets by detecting a low to high edge, and shows a frame on the high to low edge, then I imagine an inverse signal would clear the screen and keep the screen clear for the majority of the time, show the image so quickly you couldn't possibly see it with the naked eye, then clear the screen right back again. You may be able to barely discern static elements of the display if you had amazing vision, but otherwise it would appear totally blank. This is what I think is going on with my unit at least, and at this point I'm just going to see what happens if I wire up the BennVenn LCD display since it's the path of least resistance. However, if I am right, and this is the only difference between a Hayato Lynx II display vs a Mikey Lynx II display, then it might be possible to work around these issues with a factory LCD by simply inverting PIN21, or in the case of a C104129-001 motherboard rewiring pin 21 on the LCD header to receive the signal from TP27 instead. I might actually try this, but not before I make sure the BennVenn LCD works to rule out other possible issues.

 

Are you saying you have an early revision of the Lynx II that is actually using the Lynx 1 chipsets? Did you mention that before? If that is the case, then you actually have to use a BennVenn screen designed for the Lynx 1 in that Lynx 2 and even then, I'm still not quite sure it will work. I ran into one of those older Lynx II models previously and at that time, the only way to add a replacement LCD to it, was to get a McWill for the Lynx 1 and install it into that Lynx 2. Aside from a jumper I had to solder on the LCD screen, it was pretty much the same installation as the Lynx II screen. But that did work. However, I had to be creative with the screen install since the Lynx I screens from McWill at the time were not the same as the Lynx II so I do remember it being a pain to install the screen physically because of this.

 

[oski_98]

Well I was wrong anyway. I've been in touch with BennVenn and they pointed out that TP27 is not exactly the inverse of RST. They are not in sync. Apparently TP27 pulses high at the start of a frame and RST pulses low at the end of a frame.

 

There's some good news though. I installed a BennVenn Rev6b LCD for C104129-001 motherboards (early revision Lynx II with Mikey) and it works! But I'm still baking my noodle on why it doesn't work with the screen that it came with. Especially since I know that screen works with a Hayato Lynx II.

[oski_98]

I'm posting the measurements that I took from a C104129-001 motherboard (early revision Lynx II with Mikey chip) with my oscilloscope for posterity and in case they help someone else. Though I wasn't able to get the LCD that came with this unit to work, I was able to replace it with a BennVenn Rev6b LCD, and it now works.

 

|Pin |Name    |Signal   | Mean V |Frequency |Trough  |Crest    | Notes                        |
|---------------------------------------------------------------------------------------------|
|1   |+5V     |--       | 4.9  V |--        |--      |--       |--                            |
|---------------------------------------------------------------------------------------------|
|2   |+5V     |--       | 4.9  V |--        |--      |--       |--                            |
|---------------------------------------------------------------------------------------------|
|3   |DBL     |square   | 2.4  V | 3.15 kHz |  0   V |  4.9  V |--                            |
|---------------------------------------------------------------------------------------------|
|4   |P3      |square   | 2.6  V |12.6  kHz |  0   V |  4.9  V |--                            |
|---------------------------------------------------------------------------------------------|
|5   |P2      |square   | 2.6  V |25.1  kHz |  0   V |  4.9  V |--                            |
|---------------------------------------------------------------------------------------------|
|6   |P4      |square   | 2.6  V | 6.3  kHz |  0   V |  4.9  V |--                            |
|---------------------------------------------------------------------------------------------|
|7   |P1      |square   | 2.6  V |50.7  kHz |  0   V |  4.9  V |--                            |
|---------------------------------------------------------------------------------------------|
|8   |VM      |--       | 4.5  V |--        |--      |--       |--                            |
|---------------------------------------------------------------------------------------------|
|9   |CL2     |square   |  .04 V | 6.3  kHz |  0   V |  4.9  V |--                            |
|---------------------------------------------------------------------------------------------|
|10  |VD2     |--       | 4.5  V |--        |--      |--       |--                            |
|---------------------------------------------------------------------------------------------|
|11  |CLKB1   |squarish | 4.2  V | 6.3  kHz |  0   V |  4.9  V |2 MHz 40 uS bursts at 6.3 kHz |
|---------------------------------------------------------------------------------------------|
|12  |CLKA1   |squarish |  .7  V | 6.3  kHz |  0   V |  4.9  V |2 MHz 40 uS bursts at 6.3 kHz |
|---------------------------------------------------------------------------------------------|
|13  |CLKB2   |squarish | 4.2  V | 6.3  kHz |  0   V |  4.9  V |2 MHz 40 uS bursts at 6.3 kHz |
|---------------------------------------------------------------------------------------------|
|14  |CLKA2   |squarish |  .7  V | 6.3  kHz |  0   V |  4.9  V |2 MHz 40 uS bursts at 6.3 kHz |
|---------------------------------------------------------------------------------------------|
|15  |CLKB3   |squarish | 4.2  V | 6.3  kHz |  0   V |  4.9  V |2 MHz 40 uS bursts at 6.3 kHz |
|---------------------------------------------------------------------------------------------|
|16  |CLKA3   |squarish |  .7  V | 6.3  kHz |  0   V |  4.9  V |2 MHz 40 uS bursts at 6.3 kHz |
|---------------------------------------------------------------------------------------------|
|17  |DL1     |logic    |--      |--        |  0   V |  4.9  V |--                            |
|---------------------------------------------------------------------------------------------|
|18  |DL3     |logic    |--      |--        |  0   V |  4.9  V |--                            |
|---------------------------------------------------------------------------------------------|
|19  |DL0     |logic    |--      |--        |  0   V |  4.9  V |--                            |
|---------------------------------------------------------------------------------------------|
|20  |DL2     |logic    |--      |--        |  0   V |  4.9  V |--                            |
|---------------------------------------------------------------------------------------------|
|21  |RESET   |square   | 4.7  V | 60    Hz |  0   V |  4.9  V |--                            |
|---------------------------------------------------------------------------------------------|
|22  |LCD VDD |square   | 7.4  V | 3.2  kHz |  2.8 V | 12    V |Trough and crest adjusts      |
|    |        |         | to     |          | to     | to      |with contrast wheel           |
|    |        |         |12.7  V |          |  3.8 V | 21.8  V |from left to right.           |
|---------------------------------------------------------------------------------------------|
|23  |LCD TPR |square   | 7.3  V | 3.2  kHz |  2.6 V | 12    V |Trough and crest adjusts      |
|    |        |         | to     |          | to     | to      |with contrast wheel           |
|    |        |         |12.7  V |          |  3.8 V | 21.8  V |from left to right.           |
|---------------------------------------------------------------------------------------------|
|24  |LCD VSS |square   |  .1  V | 3.2  kHz | -4.8 V | 4.8   V |Trough and crest adjusts      |
|    |        |         | to     |          | to     | to      |with contrast wheel           |
|    |        |         | 3.5  V |          |-12.4 V | 5.8   V |from left to right.           |
|---------------------------------------------------------------------------------------------|
|25  |???     |square   | 3.3  V | 3.2 kHz  |  3.1 V | 3.6   V |Trough and crest adjusts      |
|    |        |         | to     |          | to     | to      |with contrast wheel           |
|    |        |         | 4.5  V |          |  4.3 V | 4.8   V |from left to right.           |
|---------------------------------------------------------------------------------------------|
|26  |GROUND  |--       | 0    V |--        |--      |--       |--                            |
|---------------------------------------------------------------------------------------------|