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#1 2017-03-05 21:15:38

ScutBoy
Member
Registered: 2014-05-25
Posts: 157

New to me...

This came home with me yesterday from the FreeGeek. First TRS-80 I've owned.

Works great, and very clean - came with the original dust covers!

Now I'll have to see how far their BASIC diverges from Applesoft/Integer BASIC smile


Model_III.jpg

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#2 2017-03-05 21:29:41

jt
Member
From: Bermuda Triangle, NC USA
Registered: 2014-05-21
Posts: 1,406

Re: New to me...

Sweeeet!

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#3 2017-03-06 18:07:07

mcdermd
Member
From: Corvallis, OR
Registered: 2014-05-12
Posts: 962
Website

Re: New to me...

Real Nice! Score with the dual-drive model. 48k RAM? Those manuals look nice too.

Mine came from the dumpster! When I first got it, it immediately smoked a cap in the PSU. The office smelled for days.

Last edited by mcdermd (2017-03-06 18:09:20)


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#4 2017-03-06 19:37:39

Eudimorphodon
Member
Registered: 2014-09-02
Posts: 525

Re: New to me...

ScutBoy wrote:

Now I'll have to see how far their BASIC diverges from Applesoft/Integer BASIC smile

If you ever used BASICA/GW-BASIC on an MS-DOS machine Tandy BASIC will feel much closer to that than either Apple BASIC, but of the two it's more closely related to Applesoft. Compared to Applesoft it's mostly blessed with more and better string functions, and also sticks closer to generic Microsoft BASIC-80/MBASIC command syntax while Applesoft was munged to make it somewhat more compatible with Integer.

Hope you have fun with it. I've never managed to get my paws on a Model III, myself. I have a Model I and a pair of Model 4s (A 4 and a 4P, actually), so technically I don't suppose I'm missing much because the 4 can do everything the III could and the III didn't do much a I couldn't do. But I do love the silver paint job; Tandy went over to the dark side when they made the 4 white.


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#5 2017-03-06 21:36:39

ScutBoy
Member
Registered: 2014-05-25
Posts: 157

Re: New to me...

mcdermd wrote:

Real Nice! Score with the dual-drive model. 48k RAM? Those manuals look nice too.

Yes - dual drives and 48K. The cassette player looks almost brand new - hopefully I'll never have to use it; I remember the bad old days of cassette software on my Apple ][ wink

Due to the law of accumulation, I may now inherit a basket-case Model 1 with Expansion Interface from a friend who saw this and said "I didn't know you liked these things..." According to him its filthy and hasn't worked in years "but all the pieces are there" which according to him means monitor, Expansion box, and two floppy drives. I guess we'll see...

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#6 2017-03-06 23:09:17

jt
Member
From: Bermuda Triangle, NC USA
Registered: 2014-05-21
Posts: 1,406

Re: New to me...

Thank the great Finagle I'm not tempted by these beasts (very much roll) in today's world. I've been researching a good Basic/Compiler to use on my Orange pi ONE and running across scads of incendiary blather about how learning Basic ruins the minds of young programmers for learning anything  .  .  .  dunno, but by context I'd have to say "useful?" That goto should have been sent straight to along with it seems to be the consensus of this new crop of mavens. I cut my digital teeth programming in basic on the Model III  .  .  .

.  .  .  could that be what happened to me? lol

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#7 2017-03-07 01:31:15

Eudimorphodon
Member
Registered: 2014-09-02
Posts: 525

Re: New to me...

ScutBoy wrote:

According to him its filthy and hasn't worked in years "but all the pieces are there" which according to him means monitor, Expansion box, and two floppy drives. I guess we'll see...

Heh. If it's too much of a steaming pile for you to deal with hit me with an IM or something, I might be interested in buying it off you to use as a parts unit for mine. Mine works, but it's... very well loved and feeling pretty brittle anymore, particularly the keyboard.

(Tandy didn't exactly break the bank when it came to quality for those machines. By comparison, I sort of feel like I could chuck my Commodore PET 2001 off a building and just end up hurting the ground. Of course, it doesn't hurt that Commodore made desks and file cabinets before they got into computers and brought their heavy steel folding tooling along for the ride.)

Last edited by Eudimorphodon (2017-03-07 01:32:23)


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#8 2017-03-07 18:33:10

ScutBoy
Member
Registered: 2014-05-25
Posts: 157

Re: New to me...

I pulled apart the keyboard unit of the Model 1 last night, and cleaned up the two boards best I could with some alcolhol.

Initial test without the Expansion Interface connected resulted in the power light coming on, and a small flash on the monitor, but no other activity on the screen.

No combo of powering on with the Break key or reset key held down, or pressed after power-on made any difference.

A quick check of the components on the board didn't reveal anything getting particularly hot.

Seems like from the troubleshooting docs I've found I should start to check that power is correct and available at various points around the board.

I'm guessing the lack of display is not the monitor itself, but with that funky DIN plug it's not easy to verify by using another monitor.

Any hints on how to proceed are welcome, otherwise I'll putz through the SAMs book and the other troubleshooting docs I've run across on line.

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#9 2017-03-07 19:33:03

Eudimorphodon
Member
Registered: 2014-09-02
Posts: 525

Re: New to me...

ScutBoy wrote:

I'm guessing the lack of display is not the monitor itself, but with that funky DIN plug it's not easy to verify by using another monitor.

The DIN pinout is similar but not identical to the AV pinout on several other 8-bit home computers like the VIC-20, Atari 800, etc. Video is on pin 4, the stated difference is it uses pin 5 for the ground instead of pin 2. (Oddly, I know at one point I had a cable that would work with either my Atari 800 or the TRS-80, so it's possible you might run into a prefab cable that works. One for a C64 probably *won't* work because the C64 uses pin 4 for a rarely-used audio function.) The 5-pin DIN connector itself is, thankfully, really easy to find as DIN connectors go (it's the same used for MIDI cables), here's a quick rundown on how to make a cable yourself.

Power supply is definitely a place to start. As I recall, Radio Shack made some weird design decisions for the TRS-80 in order to save a few bucks on manufacturing, among those was using a power supply built around discrete components instead of single-package regulators (7805/12s like the contemporary Commodore PET used) because the individual bits were literally a few cents cheaper despite the additional board space.

Like the original Commodore PET the TRS-80's video circuitry doesn't need any CPU intervention/initialization to start running; if the video circuitry is good but you have bad RAM, ROM, or CPU you should still get a screen full of garbage... which means ruling out a bad monitor is also a good step.


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#10 2017-03-07 21:07:23

Eudimorphodon
Member
Registered: 2014-09-02
Posts: 525

Re: New to me...

... another note about TRS-80 monitors: the 5v output on the monitor plug is there to drive an optoisolator circuit inside the monitor (yeah, weird). The monitor is just a barely-modified cheap-y RCA TV set, and it's a "hot chassis" design. There's a potential danger with such a design of something or someone getting zapped across a common ground, so Tandy elected to fix it with an optoisolator powered by the computer instead of adding an isolation transformer. (Which, again, would have been more expensive.) It's *possible* that circuit could be acting up. Not likely, but possible, which is another good reason to try it with another monitor.


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