Subject: TRS-80 Mod I Video Display

From: "Erik S. Klein" <[email-masked]>
Date: Mon Jul 21 16:35:54 2003

I've got a TRS-80 Mod 1 with a bad display.  There is a horizontal scan
line in the center of the screen but no vertical sweep.

Is anyone familiar enough with these displays to give me repair hints?
Failing that, does anyone have a working one lying around that they'd
part with?

Thanks!

   Erik Klein

   www.vintage-computer.com/vcforum

   The Vintage Computer Forum

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From: Fred Cisin <[email-masked]>
Date: Mon Jul 21 16:37:22 2003

> Failing that, does anyone have a working one lying around that they'd

Don't have any, any more,  but are you aware that you can connect an
ordinary composite video monitor, instead?

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From: "Erik S. Klein" <[email-masked]>
Date: Mon Jul 21 16:38:51 2003

> ordinary composite video monitor, instead?

Unfortunately all of my composite video is in storage with my Apple,
Atari, Commodore and other systems.

All I've got left at the house, until I finally move, is a few new
machines and a few S-100 systems I held back lest the movers trash them.

I may go on a local hunt this weekend, but I doubt I'd find anything
worth my time.

Wouldn't I have to make a cable for composite to the 5 pin on the RS or
is there a composite out port I've missed?

Thanks!

   Erik Klein

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From: Fred Cisin <[email-masked]>
Date: Mon Jul 21 16:41:57 2003

> machines and a few S-100 systems I held back lest the movers trash them.

As a possibly impractical or inconvenient temporary alternative, does your
TV have composite in?  or composite in of your VCR and then to your TV?

Do any of your "new" machines have video IN?  Or get one of the cheap
USB "video capture" external boxes.   Cable the TRS-80 to a video
capture unit, and display on the "new" computer's monitor, to let a half
gigahertz pentium machine act as a "video server" for the TRS-80.

> is there a composite out port I've missed?

You'll need to solder at least two wires to make a cable from 5 pin DIN to
composite.  (in a pinch, you could take cut up a DIN cable and a composite
cable and twist them together).
For permanent use, drill a hole in the case and install an RCA jack.

I don't remember the pinout, but I think that the video 5 pin DIN had
video, ground,  and 5V?
I don't even remember which of the three side by side 5 pin DINs was the
video.  IBM saw the OBVIOUS problem inherent in that, and in typical
IBM style only had TWO side by side 5 pin DINs on the 5150.

--
Grumpy Ol' Fred     		[email-masked]

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From: [email-masked] (Tony Duell)
Date: Mon Jul 21 16:48:01 2003

> Is anyone familiar enough with these displays to give me repair hints?

I have the service manual for the original (no green filter, controls in a
horizontal row at the bottom right) somewhere, and I'll dig it out if you
want to get inside. 

However, a word of warning. This is by far the most unpleasant monitor 
I've ever worked on. It's a converted RCA portable TV (the conversion 
consisted of removing the tuners and IF plug-in PCB and fitting a video 
input PCB in the IF PCB slot). This means that the 110V model is hot 
chassis -- the video input PCB contains an optoisolator so the computer 
is not directly connected to the mains. Since you need to work on the 
vertical deflection circuit, you'll be working on the 'hot' part. If you 
don't have an isolating transformer then don't even think about working 
inside this monitor with the power applied!

The 230V model is a bit more pleasant. The TV's PSU was strictly 110V 
only, so it needs a transformer for 230V mains. Radio Shack used a proper 
double-wound isolating transformer, which means the chassis of the 230V 
model is isolated from the mains. The video input board on that model is 
just a transistor buffer stage, no optoisolator.

Let me know if you want me to dig out the service manual and talk you 
through the vertical deflection circuit.

-tony

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From: [email-masked] (Tony Duell)
Date: Mon Jul 21 16:49:30 2003

> I don't remember the pinout, but I think that the video 5 pin DIN had

Yes, composite video, ground, and 5V from the CPU to the monitor to power 
the input buffer on the video interface PCB. One thing to be aware of is 
that on 99% of 5 pin DIN plugs, pin 2 is ground. On this one, pin 2 is 
not connected. So a normal audio cable (say 5 pin DIN to 4 RCA plugs, 
which is a common tape recorder lead over here) doesn't work!

The pinout (from the TRS-80 TechRef) is : 

1 : +5V
2 : N/C
3 : N/C
4 : Composite video
5 : Ground

Note that the pins are numbered in the order 1, 4, 2, 5, 3

> I don't even remember which of the three side by side 5 pin DINs was the

The middle one!

-tony