TRS-80 Questions

[+save2600]

Have you gotten that other pot freed yet? That's the first thing I'd do. Lines across the screen does not necessarily mean you can see text yet. Get that other pot freed and increase the contrast. You should then see text on the screen. Failing that, then yes - start dismantling that damn thing and proceed to examine the chips. Pay close attention to their notches. They may not always plug in the way you think they should - especially the CPU.

[Tempest]

Ok I got the second dial freed up, still nothing new. I guess I'm going to have to take the boards apart and see what I can see. I'm starting to feel a bit better about this now that there's a picture (sort of) on the monitor. Maybe I can do this after all?

 

Tempest

[+save2600]

Yep!

 

Edited May 25, 2010 by save2600

[Tempest]

Well I took the boards out and reseated all the chips, still nothing. I'm starting to wonder if the problem isn't the ribbon cables that connect the boards. Two or three of them are really badly creased and one looks like it has a hole sort of punched in it. I don't know how resilient they are, but I'm guessing that they need to be replaced. Does this sound like a possible cause of my problem? If so, where can I get replacements? They're the larger ones, not the smaller ones.

 

Tempest

[+save2600]

Take a DMM and switch it to continuity mode with alarm. If the connection beeps, you're okay. Low voltage ribbon cables rarely ever die. Cold solder joints connecting them however are common.

 

So..... were you ever able to get that other pot (the contrast control) loose to adjust that?

Edited May 25, 2010 by save2600

[Tempest]

Take a DMM and switch it to continuity mode with alarm. If the connection beeps, you're okay. Low voltage ribbon cables rarely ever die. Cold solder joints connecting them however are common.

 

So..... were you ever able to get that other pot (the contrast control) loose to adjust that?

Yes I was, took forever though.

 

I'm not even sure where to begin with a DMM. I'm starting to think this thing is just plain screwed, that's probably why it was out in the trash to begin with!

 

Tempest

[+save2600]

Fucko Matt,

 

C'mon man... you can work a Digital Multi-meter. Testing for continuity is one of the simplest things man can perform. Positive (red) lead to one end, Negative (black) end to the other. When it beeps, you have continuity... meaning the connection is more than likely good as she sits.

 

Don't give up on me now... methinks you're pretty close at resurrecting this damn thing...

Edited May 25, 2010 by save2600

[JamesD]

To answer the original question...

 

I learned to program on the Model I and then programmed some stuff for my high school on a Model III.

The Model III has a better keyboard, lower case is standard, and a higher clock speed than the Model I.

It's also more reliable. I also think it had a faster cassette interface but that's mostly a software thing.

The Model IV adds CP/M support, 80 columns, and 64K. It is supposed to offer a Model III mode so I guess that makes it best if you care about the upgrades from the III.

 

However, someone has announced an SD interface with RAM for the Model I/III.

If you don't need an expansion interface for RAM and disk drives, the Model I becomes pretty reliable, it's smaller, and with some other mods, *I* like it best... however I still like the Model III keyboard better.

 

As for modifications...

There are lower case mods.

There were several high speed mods for the Model I, some of which are pretty easy to do and make it faster than the Model III.

If you are willing to build a video cable, you can hook it up to an LCD TV/monitor that accepts composite video. That combined with an SD interface makes it WAY smaller than the other two.

I really don't need CP/M but there is supposedly a mod for that as well.

There are even hi-res graphics mods for the machine.

 

If anyone is interested, 'The Custom TRS-80 and Other Mysteries' is a good place to find some of this stuff.

 

For that book and all other things TRS-80 I suggest you download the 'trs-80 archives' torrent. Warning, it's almost 17GB and not set up so you can just grab the files you want. It's a set of iso files you can burn to disk.

It has books, magazines, software, newsletters... pretty much anything remotely related to the TRS-80.

[kool kitty89]

Some of the games are really amazing for this system even with the limited hardware. There is a game that is like "House of the Dead" with parallax scrolling and everything. Really amazing what some people did back then!

Indeed ...and to clarify what I mean by "hilarious", is how astonished you are after seeing some of these games, how well they look and play. They really are that good. Not much in the way of sounds though

 

http://www.youtube.com/results?search_query=trs-80+game&aq=f

 

Quite a few games posted on youtube, a lot seem to have some sound... How is it generated though? Is there an onboard beeper (so sound would be simple clicks, or pulses -more complex depending on the CPU resource used -much like the Apple II). I've read that some model 1 games were intended to use an AM radio for sound created by the rather intense RFI.

This really sounds like some Apple II games:

http://www.youtube.com/watch?v=uIUxmqe3jA4

 

This one even has speech:

http://www.youtube.com/watch?v=gIxmbjAq_lM

[JamesD]

Some games play sound through the cassette out attached to a speaker.

If you think that's cool, you should see what someone has done to increase the vertical resolution and create gray scale images... all through software.

[Tempest]

C'mon man... you can work a Digital Multi-meter. Testing for continuity is one of the simplest things man can perform. Positive (red) lead to one end, Negative (black) end to the other. When it beeps, you have continuity... meaning the connection is more than likely good as she sits.

 

Don't give up on me now... methinks you're pretty close at resurrecting this damn thing...

It's not that I don't know how a DMM works, it's just that I have no clue where to start or what to test. I don't know what the problem is so diagnosing it is an almost impossible task. If I had some idea what the issue was then I would at least have a starting point.

 

Another thing I forgot to mention is that the lines on the monitor only appear when the brightness is turned up high (meaning the screen is a light gray instead of black). I'm not sure if this implies anything or not.

 

Tempest

[+save2600]

It's not that I don't know how a DMM works, it's just that I have no clue where to start or what to test. I don't know what the problem is so diagnosing it is an almost impossible task. If I had some idea what the issue was then I would at least have a starting point.

 

Another thing I forgot to mention is that the lines on the monitor only appear when the brightness is turned up high (meaning the screen is a light gray instead of black). I'm not sure if this implies anything or not.

 

Tempest

Yeah, the grey screen and lines imply that the monitor does indeed work. But you're still not getting any characters to show after freeing the other pot huh?

 

And the DMM thing - gotcha. Well, I thought you were thinking one of the connectors or ribbon cables was bad. They can have sharp angles to 'em and still work fine. The problem I've seen lies within the larger cable that goes between the drives, disk controller and CPU. That one you might want to buzz out if after you get the computer to boot and it doesn't want to read a disk. Come to think of it, if you have disk controller problems (like the card itself or that ribbon cable is funky), the computer may not boot. I was going to suggest removing the cable from the controller card to the CPU, but be extremely careful - IF you attempt that. It's a PITA to put back on if the cable is flimsy and weak after all these years.

 

So have you reseated the chips on the CPU board yet?

Edited May 25, 2010 by save2600

[Tempest]

It's not that I don't know how a DMM works, it's just that I have no clue where to start or what to test. I don't know what the problem is so diagnosing it is an almost impossible task. If I had some idea what the issue was then I would at least have a starting point.

 

Another thing I forgot to mention is that the lines on the monitor only appear when the brightness is turned up high (meaning the screen is a light gray instead of black). I'm not sure if this implies anything or not.

 

Tempest

Yeah, the grey screen and lines imply that the monitor does indeed work. But you're still not getting any characters to show after freeing the other pot huh?

 

And the DMM thing - gotcha. Well, I thought you were thinking one of the connectors or ribbon cables was bad. They can have sharp angles to 'em and still work fine. The problem I've seen lies within the larger cable that goes between the drives, disk controller and CPU. That one you might want to buzz out if after you get the computer to boot and it doesn't want to read a disk. Come to think of it, if you have disk controller problems (like the card itself or that ribbon cable is funky), the computer may not boot. I was going to suggest removing the cable from the controller card to the CPU, but be extremely careful - IF you attempt that. It's a PITA to put back on if the cable is flimsy and weak after all these years.

 

So have you reseated the chips on the CPU board yet?

Yes I reseated all the chips, except those three under the little board as I didn't want to pry off that board (it seemed stuck there). I pushed them down the best I could though.

 

The system attempts to read from one of the disk drives for a bit before stopping after I turn it on so I'm guessing the disk controller is still good. I might have a TRS-80 disk floating around that I can try and see if it actually does read from the disk (even if I can't see it).

 

Tempest

[George Phillips]

One thing you can do is hold on the BREAK key and then turn on the power (or hold on BREAK and press the orange reset switch). This tells the machine to ignore the disc drives and go into BASIC. You should see a "Cass?" prompt (press ENTER) and a "Memory Size?" prompt (also press ENTER). There will be some copyright information and then the BASIC "READY" prompt. But mainly even just the "Cass?" prompt will show that the machine is basically working.

 

Sound on the machine comes by way of the cassette tape storage. It can save and load programs from cassette tapes which means it essentially has microphone and speaker connections that normally attach to a cassette tape player. This required a bit of work to set up so only games ever did audio output.

 

Incidentally, I've made some programs that push the TRS-80 graphics about as far as they can go. Check them out starting here: http://members.shaw.ca/gp2000/breakthrough.html

 

My favorite is the bouncing ball:

 

http://www.youtube.com/watch?v=kMUj47-8Sqs

 

I daresay they'd be cool to see on the real machine. As far as I know only one Model III in the world has ever run them.

[+save2600]

Neat stuff there George! Say... since some/most games utilize sound and it runs through the cassette interface, does it stand to reason we could hack our own cables to hook to a speaker or amplifier and then a speaker? I'm thinking that's got to be a line level output and that the cassette player amplifies the signal to drive its internal speaker. And I was shocked to hear one of those games had digitized speech even!

Edited May 26, 2010 by save2600

[JamesD]

Neat stuff there George! Say... since some/most games utilize sound and it runs through the cassette interface, does it stand to reason we could hack our own cables to hook to a speaker or amplifier and then a speaker? I'm thinking that's got to be a line level output and that the cassette player amplifies the signal to drive its internal speaker. And I was shocked to hear one of those games had digitized speech even!

Actually, Radio Shack used to sell a little amplified speaker you could directly plug the cassette cable into.

It was never officially for use with their computers but I saw a lot of machines with those.

[JamesD]

Some games play sound through the cassette out attached to a speaker.

If you think that's cool, you should see what someone has done to increase the vertical resolution and create gray scale images... all through software.

FYI, I was talking about George's stuff.

[+thegoldenband]

It never ceases to amaze me what these machines can do -- George's stuff is truly impressive. I'm rooting for Tempest's machine to come back from the dead!

[Tempest]

It lives! Holding down the break key works! I get the Cass? Memory? and Basic copyright message. Err.. so what does that mean? Is it normal to hold down the break key? Does that mean the disk drives are bad? I don't have a TRS-80 disk to test it with.

 

Tempest

[Mirage]

:thumbsup: No, it doesn't mean the drives are bad, it just means you don't have a disk. Break just bypasses them to go straight into BASIC.

[+save2600]

Yay, I bet it all works then! Just need a DOS disk and some games now to test. I totally forgot about holding break down upon startup. +1 to George!

 

Well, at least you got some of the preventative maintenance stuff done and got to know the system a little better

[Mirage]

I think I'm going to make a cassette cable for mine:

 

http://www.8bit-micro.com/data-cable.htm

[+save2600]

I think I'm going to make a cassette cable for mine:

 

http://www.8bit-micr.../data-cable.htm

Sweet! Haven't bothered looking into the pinouts yet, so that saved some time. How many pages down was that in Google?

Edited May 26, 2010 by save2600

[Tempest]

I think the disk drives work as well. I got the Diskette? prompt when I put a disk halfway in.

 

Now I just need to get some games. What are the best ones to get? I played Thirteen Ghosts, Zaxxon, and some Astro Fighter clone at CCAG that were pretty interesting (Zaxxon was surprisingly competent). I'm guessing I should start with the Big Five titles.

 

So there's no sound unless you have something hooked to the cassette port? I could have sworn the Model 4 I was playing at CCAG had sound.

 

BTW the badge on this machine says "Level IV Products" and "48K". I assume Level IV was a aftermarket thing?

 

Tempest

[JamesD]

I think the disk drives work as well. I got the Diskette? prompt when I put a disk halfway in.

 

Now I just need to get some games. What are the best ones to get? I played Thirteen Ghosts, Zaxxon, and some Astro Fighter clone at CCAG that were pretty interesting (Zaxxon was surprisingly competent). I'm guessing I should start with the Big Five titles.

 

So there's no sound unless you have something hooked to the cassette port? I could have sworn the Model 4 I was playing at CCAG had sound.

 

BTW the badge on this machine says "Level IV Products" and "48K". I assume Level IV was a aftermarket thing?

 

Tempest

I'd download the torrent I mentioned but you'll also need to transfer files to Model III disks.

If you have an old 360K drive I know there is a utility that can read/write many 8 bit formats. I used it to read my old CoCo disks. Sorry, I don't remember the name at the moment.

 

The Big Five titles were all pretty cool.

 

I'm guessing Level IV is an aftermarket RAM upgrade.