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Commodore 1084D - Sync problems with RGB

P

Paul-VT

Member
Joined
May 30, 2018
Messages
40
Location
Vermont, USA
Hi Everyone,
I have a 1084D. It works well when I use the analog luma and chroma inputs. But when I use the RGB 9 pin input either on the analog or digital switch setting, I get weird behavior.

Here's a photo of the C prompt: it looks fine right?
DSCF0011.jpeg

Here's a photo after typing a few characters:

DSCF0012.jpeg

And here's a directory listing:

DSCF0013.jpeg

Notice how the C prompt still looks good but any line with more than a few characters has out-of-sync scan lines.
The monitor is hooked up to a Tandy 1000RL/HD. The Tandy works fine with my IBM 5153. Same video cable.

Can anyone here point me in the right direction for a repair?

Thanks everyone.

-Paul in Vermont
 
When you say RGB: For a compatible signal with the 5153 , which it appears your Tandy can generate, the signals are RGBI (I= intensity) and H and V syncs of the correct polarity. So that is six signals that need to be correct, though it still works if the intensity signal is not present.But that is the way IBM did it.

Do you know for sure if a Commodore 1084D is compatible with these six IBM style signals ?

Some "RGB" input VDU's send the syncs along with the green channel or are expecting other types of sync feed. "RGB" just refers to the color signals

Assuming the Tandy RGB "system" syncs and drive signals are compatible with a 1084D VDU, or the 1084D is known to work with IBM signals and cables, then the problem you have is with the H sync, in that the picture content(video data), is affecting the H synchronization or H sync channel. In any case it appears to be an H sync issue.

Somebody may already know about the compatibility here, if not, if you could post the schematic of the 1084D VDU, I could look and see if it is expecting to see the IBM style H sync pulses, or not, when used in RGB mode.
 
The 9 pin video input on my 1084D is labelled "RGB". I assume it's 'RGBI'. I have read elsewhere online that the the Tandy 1000 outputs CGA (with extra colors).

I decided to plug my IBM 5150 which has an ATI EGA Wonder set to CGA output mode into the 1084D and found that the 1084D had no problem with that input. Maybe the Tandy's output is not really CGA? I'm much confused.

Maybe there is no problem with the 1084D after all?
 
Reading more about the Tandy 1000RL, from dosdays.co.uk:

"When Tandy introduced the RL, SL and TL models, they upgraded the video adapter to what is sometimes called ETGA or Tandy Video II. This takes either a digital CGA or mono TTL monitor"

and

"When a CGA monitor is used, the video is fully compatible with CGA and PC Jr. Tandy Video II has all the graphics modes of Tandy Video I, but adds 640 x 200 x 16".

So maybe it is a hidden incompatibility problem and I have a working 1080D. Woo-hooo!

I bought the 1080D on ebay for "parts or not working". The obvious problem was crackling and sparkling around the red anode cap. Re-seating the anode in the monitor's hole and spreading some vaseline around the underside of the rubber cap fixed this problem. For testing of the RGB input, I tried my Tandy 1000RL/HD which gave me the above results so I assumed that there was something wrong with the monitor as I have read on the web that Tandy 1000s output CGA.

I also tried the DOS "mode scan 200" command but that didn't fix the problem.

Well, at least the monitor seems to be in working order for the majority of inputs so I'm happy.

Thanks everyone.

-Paul in Vermont
 
If you're up for experiments: wIth a frequency counter or scope, compare both signals. There should be a difference, hopefully. Here is an example I took from one of my video cards outputting CGA:

1696253390697.png

This matches the CGA H.sync pulse. It could be that your Tandy's sync pulses are out of spec, or it could be that your monitor is barely locking onto the signal with its current H.hold setting. You could try to clean or tweak it (it is internal to the monitor it seems: https://archive.org/details/1084-DPALServiceManual/page/n13/mode/2up).

Another source of problems (I'm just guessing here - not very scientific I know) could be inadequate filtering on the monitor side? I wanted to check it on my 1084S, because I know the Amstrad PPC 512 outputs a slightly noisy H.sync signal (see below). When I hooked it up to the monitor immediately after powering it up, I could see similar artifacts to yours (albeit not as bad - just the first few lines of text). By the time I got my camera ready and set up the monitor warmed up sufficiently and the picture stabilized.

This is the Amstrad PPC 512 H.sync output in CGA mode:
1696262724267.png

I hope it helps as comparison
 
I hooked up my scope and got the same waveform, horizontal frequency (15.6KHz) and voltages as powerlot above.

Just for fun I tried wiggling the cable where it attaches to the back of the Tandy 1000RL. At one point I was able to obtain a perfect picture on the 1084D. Stability, color, intensity, sharpness 100% - Wow! The 1084D really does have a nice picture quality - even if it is the Daewoo model.

I suspect one or more pins is not making connection and that pin(s) was causing the incompatibility. More info soon when I figure out which one to disable.

I hope someone finds this useful :)

-Paul
 
And by 'wiggle' I meant pulling the connector outwards so that some pins were barely making contact and moving it around in a random motion until I got a good picture.
 
The result: It was pin 7 on the Tandy 1000RL's CGA output. I cut my cable open and disconnected pin 7 and voila, perfect picture.

So if for some reason you want to connect a Tandy 1000RL to a Commodore 1084D, disconnect pin 7 in your video cable..

-Paul
 
Pin 7 carries the video signal on monochrome video adapters. Could you verify if the Tandy outputs a video signal or something else on this pin?
 
I have already reassembled the cable and shrink wrapped it. I just ordered a breakout box so I don't have to cut the cable open again. I'll post more info after it arrives.

I did measure 0.7 volts on pin 7 of the output from the Tandy but did not check it with my scope :-(

The manual for the 1084D linked above shows that pin 7 is ignored by the monitor when it is in RGB Digital mode.

The Tandy can switch between CGA and Mono by rebooting with ctrl-alt-shift-v, which I tried, and it had no affect on the problem.
 
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