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Tandy 1000 TL/2 video trouble-shooting

Zippy Zapp

Experienced Member
Joined
Dec 13, 2014
Messages
254
Location
USA:CA
Hello Tandy folks,

I recently acquired a very clean Tandy 1000 TL/2 and am running into some issues. The computer seems to boot fine but the picture is garbled. I thought I had the screenshots on my phone but I will post them later. I am hooking it up to my Amiga's 1084-D monitor and have selected Digitial RGB on the back switch. At first all I got was a bunch of green and colored lines. I adjusted the monitor V controls and that did not help.

I then read in the manual that you may need to reset with CTRL+ALT+SHFT+V and I did that and I could tell there was POST showing the memory but it is corrupted and not readable. This model came with the original 20MB WD Hard drive and for now it sounds and works perfectly. Once I hit return after it boots it goes into DeskMate. I can see the blue screen and a TC logo in the middle. It switches to another mode and I can make out some text as it is clear but most is corrupted.

The screen lines are all wavy and it looks like it is out of sync or something in the graphics area is bad. I hope it is not the computer as I know exactly zero about Tandy computers. This is my first time ever owning one. I was told that the 1084 was a good fit and perhaps it is a monitor or cable issue. Although I did test the cable. I haven't tested it with my C128 yet so I can do that. I also have a CGA2RGB adapter from GGLABS I can try with another 15khz VGA monitor.

I looked for a service manual or some kind of technical reference online but came up with mostly older Tandy 1000 models. Does anyone know of a PDF for this?

Does anyone have any advice as to where I should start looking? I am not new to doing repairs on C64s and other classic computers but this is all New Tandy Territory for me. I will post some pictures later today.

Thank You.

The specs for the machine are pretty stock with 640k, no FPU, No cards, original 720k 3.5 floppy, 360k Tandy 5.25" drive and a WD 20 MB SmartDrive, XT-IDE. The jumpers at E6-E9 are in default position. I have all the original manuals and disks including the MSDOS/GW BASIC disk, and the 2 DeskMate disks.
 
I was able to exit out of DeskMate and get to a DOS prompt and at first I thought it was normal as the C:\ prompt was clear. But when I typed it started to skew the signal and a DIR listing shows in one of the screenshots I have attached below.

I guess this could be a problem with the 1084. I have no other monitors capable of RGBI. I have a Sony PVM but it is Analog only and I do have a NEC LCD that will sync to 15khz. My next step it to try with the LCD and adapter.


T1000Corrupt1.jpgT1000CPrompt.jpg
 
Here’s a shot in the dark: does the cable you’re using to connect these two have all nine pins wired through? If a TL is like some of the earlier tandy machines you might need to cut/pull out pin 7.
 
Oh. I didn't know that. Hopefully I didn't screw up anything. I tested the cable and I am pretty sure it is all the wires so hopefully that is all it is. So Pin 7 is Green - mono according to the pinout and pin 7 in TTL mode on the 1084 is supposed to be not connected but in RGB A mode it is Composite Sync. So that may be it.

Thank you for that, I will give it a shot later today.
 
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My experience with an older (EX) 1000 and a 1084 with pin 7 present was the monitor effectively grounded out that pin in digital mode and because green and mono video are cross-connected (a Tandy peculiarity) it fouled up the color rendering. That is of course a different symptom than what you’re seeing, but my thought is that there were a lot of different varieties of the 1084 monitor, maybe there’s a chance yours is getting confused by seeing video on the sync line. Kind of a long shot.
 
Yeah, this model is the Daewoo version so you never know I guess. It makes sense because when I do switch the computer to monochrome which is on Pin 7 then the 1084 screen is a bunch of green lines and unreadable. So that makes me hope that pin 7 is the culprit and the 1084 is wigging out. I do have a monochrome cable for my C128, which also uses pin 7 as monochrome, so maybe I will try that cable connected to the composite input. I am not getting my hopes up, because it is a long shot but I would be happy if that turns out to be the cause. ;-)
 
SOLVED! Thank you @Eudimorphodon, I am very grateful. My cable had all wires connected. I opened it up and snipped pin 7 from both ends to be safe and I now have a crystal clear picture. The 1084-D does not like anything on Pin 7 unless you are in Analog (Amiga) mode where it is mapped to CSYNC. Seems that the switch for digital/analog on the back of the monitor does not switch off pin 7 regardless of what the manual says.

Thanks again. Now to backup the original HD.
 
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