Hello and S-video mod for TS2068
13 messages · 2018-09-16 → 2018-10-08 · Yahoo Group era · View archive on archive.org
Participants: rowokii, mkgraham, Brad Dillon, Carl Miles, Rob Kim
Attachments in thread: 1 (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. Hello and S-video mod for TS2068
rowokii · 17 Sep 2018 03:22:59 +
Hi Everyone.
I recently joined the group. Just wanted to say hi.
Also, as most people who "discover" the TS2068, I found the noise on the composite video to be awful! I did the linear regulator mod in the Files section and while this improved things a bit, I was not very satisfied. I did see a few conversation thread mention a S-Video modification (mainly by Richard Atkinson who also had a youtube video and a web page) but not many details on how the modification was made. So, I decided to dig a bit into the video system of this computer and got the S-Video working.
I will upload the details into the Files -> 2068 Video modification -> Timex Sinclair 2068 S-Video Mod.pdf.
Before I made the S-Video modification, I also spent a bit of time overhauling the 5V supply rail in an attempt to improve the composite video, so I can't tell you if the S-Video mod alone will be satisfactory. However, with both mods, I'm am very happy with the video output now. Let me know if you guys are interested in the power supply modifications I have made.
Enough "under the hood" work on the computer... I'm off to play a few games of Manic Miner and then try to find out what else is out there for this neat computer.
Cheers,
Rob
2. Re: Hello and S-video mod for TS2068
Brad Dillon · Tue, 18 Sep 2018 14:34
That is exceptional! A you-tube video would be great! Unfortunately my modding skills are very poor so I'm not sure how I will be able to do it.
3. RE: [ts2068] Hello and S-video mod for TS2068
Carl Miles · Tue, 18 Sep 2018 10:03 · 📎 1: file
I would be interested in the modifications to the +5 Rail. You can hear the hiss through the built-in speaker although it has not been an issue for me but I am sure other would also be interested in any mods to the TS2068 these days.
Thanks for the video contribution!
Regards,
Carl Miles
Sent from Mail for Windows 10
From: [email] [ts2068]
Sent: Tuesday, September 18, 2018 4:16 AM
To: [email]
Subject: [ts2068] Hello and S-video mod for TS2068
Hi Everyone.
I recently joined the group. Just wanted to say hi.
Also, as most people who "discover" the TS2068, I found the noise on the composite video to be awful! I did the linear regulator mod in the Files section and while this improved things a bit, I was not very satisfied. I did see a few conversation thread mention a S-Video modification (mainly by Richard Atkinson who also had a youtube video and a web page) but not many details on how the modification was made. So, I decided to dig a bit into the video system of this computer and got the S-Video working.
I will upload the details into the Files -> 2068 Video modification -> Timex Sinclair 2068 S-Video Mod.pdf.
Before I made the S-Video modification, I also spent a bit of time overhauling the 5V supply rail in an attempt to improve the composite video, so I can't tell you if the S-Video mod alone will be satisfactory. However, with both mods, I'm am very happy with the video output now. Let me know if you guys are interested in the power supply modifications I have made.
Enough "under the hood" work on the computer... I'm off to play a few games of Manic Miner and then try to find out what else is out there for this neat computer.
Cheers,
Rob
4. RE: [ts2068] Hello and S-video mod for TS2068
mkgraham · 23 Sep 2018 03:14:23 +
I would also be interested in seeing the +5V mods. I was thinking about potentially just removing the inductor off the +5V line and splicing in output from a linear regulator. That would essentially mean the original regulator's output would be cut off from the entire system and the whole system would be powered by the linear regulator, and I'd be free to experiment with my own filter capacitor values until I got a smooth output. It would probably get quite hot powering the entire system off a linear regulator like that, but maybe I could mount it to the side of the RF cage to use as a heat sink or something?
--Michael
5. RE: [ts2068] Hello and S-video mod for TS2068
mkgraham · 23 Sep 2018 16:39:57 +
I actually tried this out (in regards to powering the entire 5V rail off a linear regulator) this morning just to see how it would go. The regulator got REALLY hot and intermittently shut down, causing random resets in the system, and the video didn't really look *that* much cleaner to me, so I reinstalled the inductor and took the 7805 back out of the system. That hissing sound was still getting to me, though, so I decided to look closer for a solution to that. Turns out, it's actually being caused by the coils on the inductor vibrating. So then I tried a few different inductors that I pulled off of a few random power supplies I had to see what might improve the situation. I think the best solution would be to replace the stock inductor (this is L2 I'm talking about, the one that looks like a small transformer) with one that has both a higher inductance value and a higher current rating than the original. I'm thinking maybe 330uH at 1.5A? The schematic says that section of the power supply is supposed to supply up to 1A (and specifies 230uH for the inductor).
--Michael
6. Re: Hello and S-video mod for TS2068
rowokii · 28 Sep 2018 17:23:39 +
Yes, you can't directly use a linear 5V regulator on the 15V (more like 20.5v open circuit). Since the 12V regulator is only rated for 100mA, you can't use that either. I ended up using a mini-buck converter from ebay meant for RC airplane to down convert the 15V to around 7.75V and then feed that to the 5V regulator. The linear regulator gets warm (around 55C) without any heat sink. I mounted the regulator to the RF shield to use that as a heat sink and that seems to work well.
I'm at work right now, so can't go into too much details, but I'll try to provide additional information over the weekend.
Oh, BTW, my S-Video mod breaks the sync signal going to the edge connector, so if you want to use the RGB output, you need to route the new luma signal to the edge connector... I'll try to provide additional info on this as well.
Regards,
Rob
7. RE: [ts2068] Hello and S-video mod for TS2068
rowokii · 28 Sep 2018 18:22:02 +
Oh, regarding swapping the L2.... I'm not sure if that's going to help. I think the main problem is the switching regulator is switching at audio frequency.... the inductor might be vibrating, but I think the switching noise is also being picked up by the amplifier driving the speaker... Doesn't help the opamp driving the speaker is in the same IC also doing the switching regulator....
Rob
8. Re: Hello and S-video mod for TS2068
mkgraham · 29 Sep 2018 13:43:32 +
Oh, I've already swapped the inductor and it completely eliminated the auditory hiss. I don't think it was coming from the speaker at all. But it hasn't helped the video yet. I don't know what value of inductor I put in because it was salvaged, so I ordered a new one (that I'm still waiting on) that's a higher inductance and current rating than the original, to see if that can manage to help the video at all.
--Michael
9. Re: Hello and S-video mod for TS2068
rowokii · 29 Sep 2018 20:08:34 +
Hi Michael,
That is good to know. I initially thought is was the speaker since when I put my oscilloscope on the speaker line, i saw a 100 to 200mV spikes at around 15KHz.. I powered up my unmodified TS2068 and you are right, the inductor is definitely the loudest noise source... though I can hear a fainter buzz from the speaker. Could it be changing the inductor changes the loop dynamics of the switching regulator to operate a bit above hearing range?
Please, by all means try out the power supply modification to see if you can get the video to improve.... I wish I was more methodical when I was doing my mods to document the results, but for me, I could not get the composite video to improve beyond putting the linear regulator on the SCLD. A solid stationary color didn't look too bad, but on things like load screen of Cybernoid, there is a checker color pattern on the wings and it would flicker like crazy.
Here's my list of power supply changes I tried and my totally subjective observation on video quality...
Best - Linear regulator on the SCLD, with 10uF caps on most of the the .1uF decaps near every chip, especially near the memory chips on the bottom. (stock regulator on the rest of the 5V)
Same - 1MHz switching regulator powering everything with the 10uF decaps. (Stock regulator disabled) The problem with this was the regulator would periodically misbehave and put out 1V Pk-Pk noise on the supply which would mess up the computer.
Very close second - The 1MHz switching regulator set to 7.75V feeding the linear regulator. This powers everything with the 10uF caps. I measured around .5mA draw by the computer and this is too high a current for the linear regulator to handle directly from the 15V supply rail, which is why the pre-regulation is needed. (This is what I am using now)
The using S-Video and the supply mod almost completely make the flicking on the load screen disappear. (I can see faint waving during load, but I have to look close).
I tried the RGB output and the video quality is similar to the S-Video output. The color is "correct" spectrum color. You do have to have a video scalar to convert to higher resolution unless you have a 15KHz RGB monitor (which I don't). I'm not sure if I'm doing something wrong, but "BRIGHT" has no effect in RGB. Added bonus for this is the lighter vs darker black doesn't matter so looks better in games.
I tried the RGB output on the stock TS2068 with no modification and my scalar board can't lock to the video... I think the video source has too much noise...
Rob
10. Re: Hello and S-video mod for TS2068
mkgraham · 30 Sep 2018 15:54:59 +
For what it's worth, I find that the colors look like the correct Spectrum colors (to me, at least) on my TV if I just turn the brightness down.
--Michael
11. Re: Hello and S-video mod for TS2068
rowokii · 30 Sep 2018 15:22:45 -
I use a Dell LCD with multiple input (s-video, composite, vga and dvi) input with my TS2068. I share this monitor with other computers, so while I can get the colors to be close to spectrum colors by making adjustments, that makes the colors for my other computer look bad. It doesn't have a save settings options that I can easily switch different settings for different inputs... oh well.
Turning down the brightness definitely helps with bright black (gray) vs not bright black (black)....
I think I might have a way fix the composite / svideo colors on this machine, but waiting on parts to try out my idea....
Rob
12. Re: Hello and S-video mod for TS2068
mkgraham · 06 Oct 2018 18:07:13 +
Well, I finally got my inductors in, after USPS sent them to the wrong city three times...
The results are not as good as I hoped, but about as good as I expected. The audio is definitely cleaner, and I can't really hear the 'hiss' at all, same as the other random inductor I tried. The video is much better than the other random inductor, but I don't think it's necessarily any better than the unmodified system. The edges of the frame might be less 'wavy' but I still have a crawling lines/shimmering effect all over the screen. So it might still be worth a full linear regulator mod to see if that helps. Or maybe I'll do a replacement of the electrolytic caps first, as these might be getting to the age where they're losing some of their filtering capability.
I forget whether I mentioned it in my earlier email, but this is a 330uH, 3A inductor that I installed in place of L2.
--Michael Graham
13. Re: [ts2068] Re: Hello and S-video mod for TS2068
Rob Kim · Mon, 8 Oct 2018 18:35:
Hi Michael,
Good stuff. I'm not sure I want to start modifying the other stock TS2068 yet, but I think if I do, I'll start from doing your mod first...
If you are going to replace electrolytic caps, it might be worth it for you to add some additional caps as well. I found adding 10uF caps parallel to the .1uF caps that already exist helps to lower noise (especially ones near the memory chips)... Just watch out for the polarity and double check before you add the electrolytic caps since they are different for each position..
Regards,
Rob
On Saturday, October 6, 2018, 11:16:36 AM PDT, [email] [ts2068] <[email]> wrote:
Well, I finally got my inductors in, after USPS sent them to the wrong city three times...
The results are not as good as I hoped, but about as good as I expected. The audio is definitely cleaner, and I can't really hear the 'hiss' at all, same as the other random inductor I tried. The video is much better than the other random inductor, but I don't think it's necessarily any better than the unmodified system. The edges of the frame might be less 'wavy' but I still have a crawling lines/shimmering effect all over the screen. So it might still be worth a full linear regulator mod to see if that helps. Or maybe I'll do a replacement of the electrolytic caps first, as these might be getting to the age where they're losing some of their filtering capability.
I forget whether I mentioned it in my earlier email, but this is a 330uH, 3A inductor that I installed in place of L2.
--Michael Graham
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