Author Topic: EEVblog #645 - TRS-80 Model I Retro Computer Teardown  (Read 22438 times)

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Offline amyk

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Re: EEVblog #645 - TRS-80 Model I Retro Computer Teardown
« Reply #50 on: July 30, 2014, 09:48:14 am »
Hey, the oscilloscope on the upper right is upside down, turn it around before all the calibration data falls out ;)
Sorry, the near-symmetry of that screenshot tempted me...
 

Offline VK3DRB

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Re: EEVblog #645 - TRS-80 Model I Retro Computer Teardown
« Reply #51 on: July 30, 2014, 01:37:04 pm »
A few other points...

Loved the tear down of an old friend, the TRS-80.

Tarnished pins is quite common on old chips - a common sight on old digital clock chips. It has to do with the plating on the pins... maybe some had silver content.

The shimmering of the image was NOT due to beating with the video camera. It was a common feature of the TRS-80 and the System-80 due to 50Hz interference superimposing on the video sync signals, causing a slight time variance in the horizontal and vertical sync signals. The varying intensity is however caused by the beating with the camera frame rate. For the System-80, good shielding of the video signal helped a great deal. The monitor on the System-80 could be any TV that was modified (I modified a GAC B/W 12 inch portable - perfect TV for the job).

It is pronounced "ALPS" as in the mountain range, not A.L.P.S. Alps still make great key switches. They also made 3.5 inch diskette drives for IBM PCs. A Japanese company, they go all the way back to 1948.

Billy Gates wrote that BASIC interpreter I believe... one of the last pieces of hands-on hacking work he ever did. People forget Gates made a lot of money out of that Microsoft BASIC, well before the IBM made the PC.

I am sure the TRS-80 booted up with "TRS80>" as the prompt... must be a different ROM. Dick Smith's System-80 came up with "Ready>". The System 80 had 16K of RAM and if I recall upper and lower case characters up to 80 columns across. In some ways better than the TRASH 80, but the build quality was atrocious - absolutely terrible in comparison to the TRS-80. If someone has a System-80 they should give it to Dave to do comparative EMI measurements. The spectrum analyser would not only slow, it would have heart failure :).

Thanks Dave once again for the teardown and the excellent quality videos! Its like being there.

PS: One of Dave's CROs in the background was on the shelf upside down and another was right side up. Not sure what the go there is.
 

Offline GeorgeOfTheJungle

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Re: EEVblog #645 - TRS-80 Model I Retro Computer Teardown
« Reply #52 on: July 30, 2014, 01:52:38 pm »

PS: One of Dave's CROs in the background was on the shelf upside down and another was right side up. Not sure what the go there is.


Yes Dave, seen from Spain everything but the scope on the right is upside down!
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Offline RupertGo

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Re: EEVblog #645 - TRS-80 Model I Retro Computer Teardown
« Reply #53 on: July 30, 2014, 01:55:59 pm »
I'm sure the upside-down CRO is just there so we in the Northern Hemisphere can read the screen properly.

There was a big 6502-v-Z80 division at my school, which boiled down to Atom/BBC/Apple/Commodore owners versus Spectrum/TRS/CPM/the rest. It was a posh school and I was a pauper (story of my life) so there was a lot of pressure to write smarter code to 'prove' your point. "The Z80's got more registers!" "Yeah, but the 6502's got zero page!" "You can't write re-entrant code with zero page!" "Your mother writes in COBOL" (etc).

The very best thing, though, as exemplified by the TRS-80 teardown, was that you could actually understand everything in your computer down to gate level. Even the processors were manageable - the 6502 has 3500 transistors, the Z80 8500 - if you dug down. These days, I think the biggest processor has somewhere over 4 billion transistors, and I can't count that high...
 

Offline jlmoon

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Re: EEVblog #645 - TRS-80 Model I Retro Computer Teardown
« Reply #54 on: July 30, 2014, 03:31:12 pm »
I think it would be fun (just for grins!) to build a TRS-80 clone with FPGA's and some interface goodies.  One could even use the original Level II rom set to get that "Crusty" vintage effect..  ;D
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Offline jcochran

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Re: EEVblog #645 - TRS-80 Model I Retro Computer Teardown
« Reply #55 on: July 30, 2014, 05:55:38 pm »
I think it would be fun (just for grins!) to build a TRS-80 clone with FPGA's and some interface goodies.  One could even use the original Level II rom set to get that "Crusty" vintage effect..  ;D
If you want to do that, you could start at worse places than http://opencores.org/project,t80,overview or http://zxgate.sourceforge.net/
The zxgate project has already been used to create a clone of the TRS80.
 

Offline Macbeth

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Re: EEVblog #645 - TRS-80 Model I Retro Computer Teardown
« Reply #56 on: July 30, 2014, 07:14:38 pm »
My first ever computer was not far off the Trash-80 (or Commodore PET) , I happened to like the Japanese MZ range back in the early 80's. The MZ-80K is the original with it's built in blue/white screen & cassette deck. I got the later and much nicer MZ-80A with it's proper keyboard and 2MHz Z80 and 48K RAM and, wow, a 2K screenbuffer that let me scroll through 50 lines of code! (I actually would have preferred an 80 column option than the 40x25 display though - aftermarket options coul enable it).

I learned how to code pure hexadecimal Z80 machine code from the ref manuals and POKE'ing them from BASIC DATA statements. I have to say, the Z80 was a dream to code compared to the 6502.

An interesting much larger scale and working reproduction of the Sharp Z80 on glass is here www.sharpmz.org/z80glass.htm

Oh yes, I still have it and indeed my first BBC Micro in the loft. They both still work, but a lot of the ceramic caps on the MZ-80A are coated in a white powder and the tape drive needs some attention. The Beeb, it was dead, but I recently fixed it by properly soldering some socket mounted IC's and the major work of fixing the dead keys (desoldering each one, dismantling, cleaning out with isopropyl alcohol, re-soldering!)
« Last Edit: July 30, 2014, 07:19:30 pm by Macbeth »
 

Offline nsayer

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Re: EEVblog #645 - TRS-80 Model I Retro Computer Teardown
« Reply #57 on: July 30, 2014, 07:14:52 pm »
Slightly off-topic perhaps, but when I get nostalgic I always say I'm going to create a new CP/M machine. That is, a modern TQFP z-80 with a banked memory system - 64K of user RAM and 64K combined boot and BIOS ROM and display memory. For storage, it would have SD card slot(s).

I think about that... and then realize that a Raspberry Pi is $35 and that it could just run a Z-80 emulator and the next thought is, "Meh. Fuck it."
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Offline firehopper

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Re: EEVblog #645 - TRS-80 Model I Retro Computer Teardown
« Reply #58 on: July 30, 2014, 07:42:24 pm »
I have a model 100 lyin around.. only 24K ram. room for another module though to max it out at 32k
 

Offline Dave Turner

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Re: EEVblog #645 - TRS-80 Model I Retro Computer Teardown
« Reply #59 on: July 30, 2014, 11:01:06 pm »
I recall having a lot of fun writing a 'crude' cross assembler on the PET for my Z80 based homebrew,
 

Offline jlmoon

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Re: EEVblog #645 - TRS-80 Model I Retro Computer Teardown
« Reply #60 on: July 31, 2014, 04:18:26 pm »
My first ever computer was not far off the Trash-80 (or Commodore PET) , I happened to like the Japanese MZ range back in the early 80's. The MZ-80K is the original with it's built in blue/white screen & cassette deck. I got the later and much nicer MZ-80A with it's proper keyboard and 2MHz Z80 and 48K RAM and, wow, a 2K screenbuffer that let me scroll through 50 lines of code! (I actually would have preferred an 80 column option than the 40x25 display though - aftermarket options coul enable it).

I learned how to code pure hexadecimal Z80 machine code from the ref manuals and POKE'ing them from BASIC DATA statements. I have to say, the Z80 was a dream to code compared to the 6502.

An interesting much larger scale and working reproduction of the Sharp Z80 on glass is here www.sharpmz.org/z80glass.htm

Oh yes, I still have it and indeed my first BBC Micro in the loft. They both still work, but a lot of the ceramic caps on the MZ-80A are coated in a white powder and the tape drive needs some attention. The Beeb, it was dead, but I recently fixed it by properly soldering some socket mounted IC's and the major work of fixing the dead keys (desoldering each one, dismantling, cleaning out with isopropyl alcohol, re-soldering!)

I look at my old but really immaculate condition IMSAI 8080 and the box of S100 cards above it everyday.  Sure does stir up the old late night memories using that stuff.
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Offline HighVoltage

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Re: EEVblog #645 - TRS-80 Model I Retro Computer Teardown
« Reply #61 on: July 31, 2014, 08:22:39 pm »
I'm curious about the video interface.  Since this was an early model, assembled in Fort Worth, it just seems odd that they have a PAL version that they made in the US for overseas use. 

Or maybe the video type doesn't really matter and it just scales itself to the 60 or 50 Hz input?

May be there was a big difference between the Computer industry and the TV Broadcasting industry.
I was surprised at one time, when I read that it was a Washington legislation that prevented the US to switch to PAL for TV's
Who know, may be this limitation did not apply to computer screens.

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Offline miguelvp

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Re: EEVblog #645 - TRS-80 Model I Retro Computer Teardown
« Reply #62 on: July 31, 2014, 11:59:17 pm »
You loose lines if you use a B&W NTSC TV if you want to display  B&W  PAL. I know this because my dad kept his B&W TV that he brought from the States when he was stationed in Spain. Frequency didn't matter and you could get a bit more than 480 lines by adjusting the horizontal trim but it will loose lock if you pushed it too much and never was able to display the full 525 visible PAL lines.

I forget if it did clip the horizontal as well. But it was able to show the picture although cropped.
He had a transformer that will bring the 220V down to 115V or whatever it was.

But in the late 70s there where a lot of discarded B&W TVs because everyone was upgrading to color (Spain was a bit behind the times) So I had a bunch of old TVs to use with my ZX 81. Eventually I got an Spectrum but of course I wasn't allowed to use the color TV, so I used my beaten up B&W TVs.

When I came to the States in the mid 80s my paternal grandmother gave me her portable B&W TV, and I was able to use it with the spectrum, I don't recall if there was any problems with cropping I think it displayed it all but a bit smaller (and it was a tiny TV to begin with, but I was a college student so I didn't mind, it was better than nothing).
 

Offline mahjongg

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Re: EEVblog #645 - TRS-80 Model I Retro Computer Teardown
« Reply #63 on: August 02, 2014, 12:34:09 am »
Yeah, that brings back many memories, at the time I was working for a small Dutch company called MCP, and one of the things we did was that we designed an alternative for the (very) expensive expansion interface. It was a small 15x15cm PCB that contained the floppy disk and printer interface logic, it was sold combined with a pair of BASF floppy disk drives, and had double density and the drives were  double sided. To get all the benefits from an expansion interface we also offered a service to expand the 16K in the base unit to 48K, replacing the 16Kx1bit 4116 DRAMS by 64x1bit DRAMS. It was my job to do the conversion, so I have seen and worked on dozens of model 1 innards. At home I had built an LNW-80, including the highres color extension. The things we sold for the TRS-80 eventually lead us to design out own TRS-80 clone, that technically was much closer to what later became the model III.
« Last Edit: August 02, 2014, 12:47:29 am by mahjongg »
 

Offline Clocky

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Re: EEVblog #645 - TRS-80 Model I Retro Computer Teardown
« Reply #64 on: August 02, 2014, 12:43:36 am »
 Thanks for doing this teardown, really enjoyed it. I was gifted one of these with the original expansion interface, floppy drive and monitor (original but different to the one you had) and Tandy speech synthesizer expansion available for it at the time - just last year. It also came with original manuals and a heap of micro-80 magazines.
I played with it a bit and added a 3.5" floppy disk drive for easier file transfer and larger storage capacity. Given that it has virtually no graphics mode, the arcade conversions of popular games of the time where pretty good and certainly playable.
Anyway, I cobbled together a homebrew Z80 system dubbed the "Junkbox VZ" which runs a Dick Smith VZ200/300 ROM BASIC which is based on the TRS-80 Level II ROM. The VZ had a lot of the Level II commands disabled and the particular ROM I use is one that has most of the commands re-enabled.
The webpage is crappy and needs updating, but it's here: http://users.on.net/~clockmeister/Junkbox_VZ/index.htm if anyone is interested.
None of this FPGA rubbish ;-)

« Last Edit: August 02, 2014, 01:23:38 am by Clocky »
 

Offline Macbeth

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Re: EEVblog #645 - TRS-80 Model I Retro Computer Teardown
« Reply #65 on: August 03, 2014, 05:31:31 pm »
My first ever computer was not far off the Trash-80 (or Commodore PET) , I happened to like the Japanese MZ range back in the early 80's. The MZ-80K is the original with it's built in blue/white screen & cassette deck. I got the later and much nicer MZ-80A with it's proper keyboard and 2MHz Z80 and 48K RAM and, wow, a 2K screenbuffer that let me scroll through 50 lines of code! (I actually would have preferred an 80 column option than the 40x25 display though - aftermarket options coul enable it).

I learned how to code pure hexadecimal Z80 machine code from the ref manuals and POKE'ing them from BASIC DATA statements. I have to say, the Z80 was a dream to code compared to the 6502.

An interesting much larger scale and working reproduction of the Sharp Z80 on glass is here www.sharpmz.org/z80glass.htm

Oh yes, I still have it and indeed my first BBC Micro in the loft. They both still work, but a lot of the ceramic caps on the MZ-80A are coated in a white powder and the tape drive needs some attention. The Beeb, it was dead, but I recently fixed it by properly soldering some socket mounted IC's and the major work of fixing the dead keys (desoldering each one, dismantling, cleaning out with isopropyl alcohol, re-soldering!)

I look at my old but really immaculate condition IMSAI 8080 and the box of S100 cards above it everyday.  Sure does stir up the old late night memories using that stuff.

Oh wow! Do you have a WOPR too?:-DD I love that old Wargames movie! As Hollywood films go, there was a lot of the stuff like hacking, wardialling, phone phreaking, etc. that was actually real and quite well presented. I know I was doing it all as a teen back in the '80s.
 


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