TRS-80 Model I Questions????

[DistantStar001]

I just got a TRS-80 Model I, and I wanted to know if there was anything I should be aware of before I power it up?  

 

So far, the only accessories I have for it are two original power supplies (untested at the moment, but I'm going to check them as soon as I find my multimeter) and a home made cassette cable that works great with my CoCos, but not my Model III.  I've already looked up how to splice together a composite video cable, and from what I can see it has a level 2 ROM update.  

 

Some initial questions:

 

What's the story on the original power supplies?  I know that Atari (XL/XE) and Commodore bricks are system killers waiting to happen, but what about the TRS-80?

 

What would be the best source for cassette (.wav) software?  

 

Related to above: Any recommendations for games or software?

 

Anything I'm forgetting?  Or any other recommendations that would improve or help preserve this machine?

 

 

 

Discovered a broken standoff in side, and this modification.  Curious if anyone knows what it could be?  Also, what's the best way to repair the plastics?

 

Also seems to be a reset switch.  Is that normal?

 

Edited August 25, 2021 by DistantStar001
Additional information.

[Calibus]

1 hour ago, DistantStar001 said:

I just got a TRS-80 Model I, and I wanted to know if there was anything I should be aware of before I power it up?  

Make sure you have the power supply plugged into the DIN connector closest to the power button.

All of the DIN connectors are the same - so it is VERY easy to plug the power into the video for example.

I see someone labeled the connectors for you - P(ower) V(ideo) and I assume there is a "C" on the yellow label for Cassette.

 

1 hour ago, DistantStar001 said:

What's the story on the original power supplies?  I know that Atari (XL/XE) and Commodore bricks are system killers waiting to happen, but what about the TRS-80?

I'm not aware of any issues with the original power supplies.

 

1 hour ago, DistantStar001 said:

Related to above: Any recommendations for games or software?

 

Wow - where to begin.  "Big 5 Software" was always the benchmark in my eyes for games.  There are arcade games, adventure games (Adventure International - Scott Adams, Infocom, Radio Shack titles such as Pyramid 2000, Raka-Tu)

I'd do a google search for Adventure International catalogs and browse through them looking for things that catch your eye.

A 16K cassette system is pretty limited, even some of the cassette only programs can require 32k or 48k.

1 hour ago, DistantStar001 said:

Discovered a broken standoff in side, and this modification.  Curious if anyone knows what it could be?  Also, what's the best way to repair the plastics?

A picture of the modification would help.

I've glued the standoffs back in place using JB Weld.

 

The Model 1 was (is) a true hardware hackers machine.  Lower case mods, Speedup Mods, Internal RAM mods, 3rd party expansion interfaces, 3rd party disk controllers, 3rd party disk drives...

1 hour ago, DistantStar001 said:

Also seems to be a reset switch.  Is that normal?

Again - maybe a picture is missing.  The reset button was considered to be in an inconvenient spot by some people - and hard to press when an expansion interface is connected, so it was common to see a push button wired

in parallel with the reset button.  I never did that to any of mine.

 

The Model 1 was my first computer back in 1981, I wanted an Apple II or an Atari, but they were out of my reach price wise back then.

I recommend the TRS-80 Trash Talk if you are into podcasts.

 

To get an idea of what sort of hardware hack were being done back in the 80s - do a google search for "The Custom TRS-80 and Other Mysteries" and you should be able to find a pdf version.

I still have my original copy.

 

 

Jim

 

[DistantStar001]

13 minutes ago, Calibus said:

A picture of the modification would help.

 

Thank you!!! 

 

And also...

 

Sorry about that.  I took the picture and forgot to add it!

 

Also, I do have one question about the video cable.  I know that the original monitor powered off the computers port and I'm concerned about shorting the power into the composite.  Should I clip that pin to be safe, or am I being overly cautious?  I've never had a machine this old, so I really don't want to hurt it.

[DistantStar001]

OK, so not getting a video signal.

[Calibus]

9 hours ago, DistantStar001 said:

Thank you!!! 

 

And also...

 

Sorry about that.  I took the picture and forgot to add it!

 

Also, I do have one question about the video cable.  I know that the original monitor powered off the computers port and I'm concerned about shorting the power into the composite.  Should I clip that pin to be safe, or am I being overly cautious?  I've never had a machine this old, so I really don't want to hurt it.

The small satellite PCB is the official XRX Cassette modification.  It was done to help the readability of cassette tapes.

The issue was later fixed in firmware with the newer ROM.

 

Your computer probably has the older ROM - if should say "MEMORY SIZE?" when powered up - instead of the newer "MEM SIZE?"

 

Does your computer have a long ribbon cable with a small board and 3 large ROM chips attached to it?  If so - that's another indicator of the the older ROM.

 

 

[Calibus]

6 hours ago, DistantStar001 said:

OK, so not getting a video signal.

 

Did you hook it up like this?

 

http://www.trs-80.com/wordpress/zaps-patches-pokes-tips/zaps-model-i-composite-video-cable/

 

If so - is the red power LED on the computer turning on?

If the red LED is on - then you have some troubleshooting to do - a multimeter is the minimum equipment you need, and a 'scope makes things easier.

Schematics are a requirement also.

You can find the tech reference manual online - like this

 

http://cpmarchives.classiccmp.org/trs80/mirrors/pilot.ucdavis.edu/davidk/documentation/26-2103.htm

 

[DistantStar001]

7 hours ago, Calibus said:

Did you hook it up like this?

 

http://www.trs-80.com/wordpress/zaps-patches-pokes-tips/zaps-model-i-composite-video-cable/

Yes.  This is the exact video I used to make my cable.

7 hours ago, Calibus said:

If so - is the red power LED on the computer turning on?

Yes I get a red light.

7 hours ago, Calibus said:

If the red LED is on - then you have some troubleshooting to do - a multimeter is the minimum equipment you need, and a 'scope makes things easier.

The good news is that I have a multimeter and two scopes!  The bad news is that neither of my scopes are working...  But I do have a logic probe if that's helpful?!?  It's a bit wonky (red is high, green is low for some reason), but it works.  Can't hurt to try.

 

Working with what I've got, I've checked the voltages on the RAM and processor...  The 12v line is spot on, the -5v is coming in at -5.12v, and the +5v is a touch low at 4.93v.  I tested the video out, and I'm getting practically nothing.  About 0.01v.  If I'm not mistaken, I should get at least 1v on a composite signal?  At least that's what I get off of my VIC-20.

 

Moving on to the logic probe, I'm getting activity from the RAM and processor, so I think the computer is actually doing something, even if I can't see it on my screen. This is the readout on the pins so far:

 

Z-80

Pins

1: No Activity

2-10: Flashing

11: High

12: No Activity

13-20: High

21-25: High

26-27: Flashing

28: High

29: No Activity

30-35: High

36: No Activity

37-40: Flashing

 

4116 RAM

Pins

1: No Activity

2-7: High

8: not tested as it's 12v

9: No Activity

10-15: Flashing

16: High

 

I'm also including some pictures of the board, as there appear to be several modifications, and I don't know enough to say that they're normal.

 

 

 

As you can see there are several areas where the mods were wired in from the back and some bodges.  The soldering is clean, and whoever did it seemed to have known what they were doing (from a soldering perspective), but I'm not sure how these effect operation.  

Edited August 25, 2021 by DistantStar001
Additional information.

[DistantStar001]

7 hours ago, Calibus said:

Does your computer have a long ribbon cable with a small board and 3 large ROM chips attached to it?  If so - that's another indicator of the the older ROM.

 

Yes, as pictured above.  

 

[DistantStar001]

Ok. I may have stumbled upon something. The 3904 transistor has about 4.9v at the collector, but 0.02v at the emitter? I think it's Q1.

[DistantStar001]

Update:  

 

So (thanks in no small part to the folks over at the VCFed.org) I've managed to repair the video issue!  The working theory is that someone plugged a power supply into the video port and fried the ICs at Z5 and Z6.  I've replaced them, and now I'm getting a good picture.  Unfortunately, the Keyboard is another issue...

 

I've tried paper, cardboard, Isopropyl alcohol, and DeoxIT, and so far the best I can do is get the key back for a few minutes, then as soon as it drys out, the key stops responding again. I did manage to get the "*:" key back to a reliable state, but then the ">." key went out. The mechanisms are the same as the ones on my Ti-99/4A (which was a pain in its own right), but this is being especially stubborn. The "0" key is now completely unresponsive, but the "/?" key is the most concerning, as, without it, I can't run a machine language program. 

 

 

I will admit that this computer was especially dirty when I got it (tons of dust and grime with a few creepy crawlies that breathed their last inside), but the contacts look clean. Still, I'm starting to wonder if it's time to try something more aggressive? Does anyone have any ideas as to how I can get the more stubborn keys going again? 

[DistantStar001]

Fixed!!! It was bad solder joints.

[Calibus]

39 minutes ago, DistantStar001 said:

Fixed!!! It was bad solder joints.

Excellent!  I'm glad to see you got it fixed - another Model 1 lives to run another day.