S-Video / Composite Video Color Fix..

5 messages · 2018-10-16 → 2019-04-18 · Yahoo Group era · View archive on archive.org

Participants: rowokii, topsock, david

Attachments in thread: 3 (see the archive.org item)

Preserved from the Timex/Sinclair 2068 Yahoo Group (2001–2019), which is no longer online. Text reproduced from the archive.org archive; email addresses masked.

Messages

1. S-Video / Composite Video Color Fix..

rowokii · 17 Oct 2018 03:35:40 + · 📎 3: file, file, file

Hi,


 I managed to find a way to fix the color on the TS2068....  it looks like the engineers designing the SCLD did an incomplete port from PAL to NTSC...  The fix is a bit tricky to implement with a few things to watch out for, which I can document at if anyone is interested.  I have only tested this out on my system which has the s-video output, but should work on regular composite output as well.  


 Attached is a few pics of the results.  The pictures are off my Dell LCD monitor which has Composite / S-VIdeo inputs on default settings.  The lighter black vs darker black still shows up, but reducing the brightness a bit makes that disappear. 


 On the game screen picture, the left side is without the color fix and right side is with the color fix.


 I'm also attaching the circuit I used to implement the fix.  Once again, if anyone is interested in implementing the change, let me know since there are a few details you need to know.


 Regards,


 Rob

2. Re: S-Video / Composite Video Color Fix..

topsock · 15 Apr 2019 20:42:47 +

I just re-purchased one. I had one as a kid and loved it. I forgot the colors are odd and the 64-character mode is weird on this machine. Top half has weird characters that won't clear but can see my program under them. Fine in normal, 32-character, mode. Anyway, interested in your mod for the color fix. Want red to be red :-)  

 I currently use the monitor out on 2068 to the composite video (AV) in on a Visio L13TVJ10. Picture is good but color, even after tuning with the TV menu, yielded little to no improvement. I have not considered s-video, however, the TV does have that as well as component and composite.


 Any help on best route for this TV, matches computer well in color and style, would be greatly appreciated.

3. Re: S-Video / Composite Video Color Fix..

rowokii · 15 Apr 2019 21:35:16 -

Hi Topsockpcs, 

 Well, I'm willing to walk you through the process if you are willing.  It does involve opening up the computer and making modifications to circuit board and building your own circuit.  I'm not sure how much experience you have in electronics.  I can go over the highlights maybe you can decide how comfortable you are with making the changes....


 As I said in the original message, this fix should work without doing the s-video modification... 


 High level explanation of what I'm doing... During HSYNC period, the SCLD chip (U3) generates a signal on V and U pins.  These signal goes to the IC U4, which generates the color reference pulses.  For PAL, U is positive and V alternate between positive and negative.  For NTSC, U is positive and V is suppose to be neutral.  TS2068 incorrectly generates a positive voltage on both U and V during the sync period.  So, I made a circuit to try to keep the V signal neutral during sync period.    


 First, you need to be able to build the circuit shown in the schematic of the original message.  I built the circuit on a small piece of pcb perfboard.  Only tricky part is I used a SMD PMOS for my switch, which is tricky to solder... suitable though hole version should work if you haven't dealt with SMD parts before.   You need to power the circuit with +5 and Gnd.  The VID line is connected to the center line of the composite output(- side of the C58).    You need to attach wires from IC4, pin2 and 3 to the PMOS transistor.  The C58 and IC4 sits inside the RF shield box.  I mounted my circuit inside the RF shield box mainly because it was convenient for me, but that does mean you have to keep your circuit board small if you want to do the same.


 After everything is built and installed you need to adjust the 1K resistor so that the PMOS switch is turn on only during the sync period.  When I was doing this, I used an oscilloscope, but since then, I found that I can get it close by first setting the resistor as high as it will go.  This short out the color on the left side of the screen.  I then reduce the resistor value until the color shows up again on the left side.   


 The other tricky thing is VR3.  VR3 pot in the computer adjust the V signal level.  The factory setting matches nominal V signal getting to IC4(PIN2) to be same as the reference signal level (IC PIN3).  If you have changed the VR3 setting, it would be best if you can get it back to the old setting.  First time, I used an oscilloscope, but once again, if you don't have one, you can just adjust it by trial and error.    If you haven't change the VR3 setting, it's best not to change the default....


 Anyway, I know I threw a lot at you.  Let me know if there are any parts I can clarify further.


 Regards,


 Rob

4. Re: S-Video / Composite Video Color Fix..

topsock · 16 Apr 2019 07:37:30 -

Thanks for getting back to me. I have a few questions but would rather go off-group. If you could shoot me an email I will get back to you. Just send a hello email to my username @yahoo. Thanks so much.

5. Re: S-Video / Composite Video Color Fix..

david · 18 Apr 2019 15:12:57 +

Hi Rob,


 Are there any other details that we should know about for this mod? I'm going to give it a go with my 2068, though I'll be testing the composite out. I think I have a monitor that does svideo but it's lost somewhere in the attic right now :)


 Thanks!
 David

Indexed under

Video upgrades (composite, RGB, HDMI) · Repair & restoration