Improving signal strength on Superboard II

[ronin47]

I tried a quick bread board of that circuit but with a bc338 and could not get a signal on the monitor but could be my error and quick and dirty breadboarding.

Anyway, out of the three LCD displays I have, the large one is working but it is too large. It’s 19”.

I took some photos of a known working composite signal vs the superboard and I can’t see what the difference is.

Would that circuit you guys have built possibly fix my synch issue or is it just to address the contrast? My contrast is good.

IMG_8079.jpeg


This is the superboard:

IMG_8075.jpeg

This is a Nintendo clone ntsc:

IMG_8073.jpeg


Here’s my video section:

IMG_8080.jpeg

Your video signal looks very much like mine. The circuit I added definitely helped with my sync but I did need to tweak the pot to get the best output.

[bxdanny]

Sideburn,

The display on that Craig monitor looks really nice. So it may be that the two "cheap" LCD monitors just don't have as great a tolerance for out-of-spec signals, and aren't going to sync reliably on OSI video no matter what.

Someone here mentioned seeing a ,01 uF capacitor installed across the RCA jack for video output on a C4P. And I think I've heard that LCD monitors don't really like the sharp transitions in the video generated by computers and video games. So you might try adding a capacitor between the Superboard's video output and ground, to round off the sharp corners in the signal a bit. It would be something if that's all it took to get the other monitors to display the signal reliably. I wouldn't count on it, but it's certainly worth a try. If neither that nor the added transistor and resistor idea work, you just might have to get a better-quality small LCD display.

Ronin47,

Is that a TRS-80 keyboard in your pictures? Did you somehow adapt it to work with OSI?

[Sideburn]

Sideburn,

The display on that Craig monitor looks really nice. So it may be that the two "cheap" LCD monitors just don't have as great a tolerance for out-of-spec signals, and aren't going to sync reliably on OSI video no matter what.

Someone here mentioned seeing a ,01 uF capacitor installed across the RCA jack for video output on a C4P. And I think I've heard that LCD monitors don't really like the sharp transitions in the video generated by computers and video games. So you might try adding a capacitor between the Superboard's video output and ground, to round off the sharp corners in the signal a bit. It would be something if that's all it took to get the other monitors to display the signal reliably. I wouldn't count on it, but it's certainly worth a try. If neither that nor the added transistor and resistor idea work, you just might have to get a better-quality small LCD display.

Ronin47,

Is that a TRS-80 keyboard in your pictures? Did you somehow adapt it to work with OSI?

OK I will give all of this a try. so I should be ok with a BC338 transistor then ?

I'm fine with getting a better LCD if I knew which one world work!

[bxdanny]

I have no idea about the different transistor types. As for which monitor would be more likely to work, my guess would simply be "a name brand", rather than what I think you described as cheap "no-name" ones.

[Sideburn]

Well the problem is I have been able to find a quality name brand 10” display.

[ronin47]

Ronin47,

Is that a TRS-80 keyboard in your pictures? Did you somehow adapt it to work with OSI?

Yes, it's my TRS-80 Model 1. It just happens to be under the display I was using for the OSI, but isn't used for the OSI at all and is turned off in this pic.

It came to me dead and needed a lot of work, and now has a FreHD hard disk interface, 2 slot switchable ROM, expanded RAM and sound mod. It's a really cool little machine

I've got a fair collection of machines with the TRS-80 being the oldest original machine, with examples from the late 70s up to the 90s.

I have a quite a few consoles and handhelds too.

The OSI replica was a perfect project to fit in with my collection.

[jbtech]

OK, so I tried a slightly different circuit to you, but only because I had it ready made in a drawer!! It's just a composite mod I made for an Atari 2600 (I think) that I abandoned and bought a ready made one for that included a nice cable and audio built in too.


IMG20240329145534.jpg


IMG20240329150554.jpg


And there is a definite improvement with the LCD.

This is before:


IMG20240329145249.jpg


This is after:


IMG20240329145340.jpg


However this is the CRT with it:


IMG20240329145453.jpg


And this is the CRT without:


IMG20240329145649.jpg


Personally I prefer the CRT without.

I'd be interested in what you think.

Hi, yes I think the signal level is a bit too high with that particular mod circuit and the B&W CRT looks sharper without it.

The common collector (a.k.a. emitter follower) configuration has a unity Voltage gain, its main purpose being a buffer which requires little input current but can drive a greater output load. But the unloaded composite video from the original output of the Superboard II is over 2 volts p-p and too high for a standard 1V, 75 Ohm monitor composite video input.

In the circuit I have drawn the 75 Ohm output resistor is in series with the emitter output so, assuming a 75 Ohm termination across the monitor input that signal Voltage would be halved resulting in close to ideal 1V level. So it may be worth lifting that 75 Ohm resistor from ground on your circuit and trying it in series with the output rather than parallel.

Apart from that if the brightness / contrast levels can't be adjusted sufficiently on the controls of the TV itself or by backing off R58 on the OSI 600 PCB it may suit that particular TV better to use the unbuffered original output from the Superboard II.

One of the reasons I added the buffered Composite video output to a different pin of my J2 connector was so the original output could still be used, depending on the type of display connected. For an original style black and white TV or monitor the unbuffered output would probably be fine however my colour CRT TV and LCD monitor appear better with the buffered output.

[jbtech]

I tried a quick bread board of that circuit but with a bc338 and could not get a signal on the monitor but could be my error and quick and dirty breadboarding.

Anyway, out of the three LCD displays I have, the large one is working but it is too large. It’s 19”.

I took some photos of a known working composite signal vs the superboard and I can’t see what the difference is.

Would that circuit you guys have built possibly fix my synch issue or is it just to address the contrast? My contrast is good.

IMG_8079.jpeg


This is the superboard:

IMG_8075.jpeg

This is a Nintendo clone ntsc:

IMG_8073.jpeg


Here’s my video section:

IMG_8080.jpeg

Hi, a BC338 and 100 Ohm pot. should be fine as substitutes for the BC547 and 75 Ohm resistor in that circuit. The pot. could always be adjusted to see if there is a range where the LCD monitor can lock onto the sync but it could still be more an issue with timing rather than level for that particular monitor.

The signal from the Nintendo clone looks similar on a line by line basis, it's obviously colour as the burst can be seen also the video / sync levels are closer to correct. But the number of lines per frame / field could be different between the two signals, without comparing the entire signal and vertical interval that wouldn't be apparent.

Using the output buffer did correct an issue with inconsistent syncing on my LCD TV / monitor but I have also tried a 7" LCD in-car type monitor which cycles in and out of sync continuously. I'm pretty sure that particular LCD monitor will never work with the Superboard II video signal regardless of level...

Regards, John.

[ronin47]

In the circuit I have drawn the 75 Ohm output resistor is in series with the emitter output so, assuming a 75 Ohm termination across the monitor input that signal Voltage would be halved resulting in close to ideal 1V level. So it may be worth lifting that 75 Ohm resistor from ground on your circuit and trying it in series with the output rather than parallel.

I have several different options to try for the circuit, so as you've said, putting the 75R resistor in series rather than to ground, and possibly removing the 2.2K and 3.3K resistors as per your circuit.

Apart from that if the brightness / contrast levels can't be adjusted sufficiently on the controls of the TV itself or by backing off R58 on the OSI 600 PCB it may suit that particular TV better to use the unbuffered original output from the Superboard II.

I can adjust the brightness/contrast on both the CRT and LCD, and have done so, but I've now got R58 tweaked perfectly so it works great on the CRT via the original output and also works great on the LCD via the buffered output.

One of the reasons I added the buffered Composite video output to a different pin of my J2 connector was so the original output could still be used, depending on the type of display connected. For an original style black and white TV or monitor the unbuffered output would probably be fine however my colour CRT TV and LCD monitor appear better with the buffered output.

I'm likely going to have both a CRT output and an LCD output I think, so that solves that problem neatly, though I may try some other buffer iterations.

[Sideburn]

I tried a quick bread board of that circuit but with a bc338 and could not get a signal on the monitor but could be my error and quick and dirty breadboarding.


Using the output buffer did correct an issue with inconsistent syncing on my LCD TV / monitor but I have also tried a 7" LCD in-car type monitor which cycles in and out of sync continuously. I'm pretty sure that particular LCD monitor will never work with the Superboard II video signal regardless of level...

Regards, John.

Yeah both of the non working lcd’s are those in-car type where as the working Craig lcd is a TV with tuner.