Tandy TRS-80 Model 4 Retro Computer Introduction and Teardown 

Somewhere around 18:30 I say that the Apple II used a Z80. That's not correct, not sure what I was thinking!

Nice to see this review ! I worked for a small company in the Netherlands that did all kinds of mods on the Mod4's. We started with the model 1, then the 3, and finally the 4. We made and sold them mainly for administrative purposes, working closely together with a plumber who was quite a programmer too. Of course we deemed those belt-driven floppydrives a disaster, and the first thing we usually did was to replace them with half-size double sided direct drives, mainly from Mitsubishi. We only used TRSdos on plain vanilla systems, we preferred NewDos80 for the more advanced stuff. We also thought that having room for more drives would give the possibility to put two harddisks in it. But that wasn't easy. We knew we had to use a "host interface" (now called a harddisk controller) to get any harddrive going. We could get those host interfaces (for a fraction of the cost of Tandy's), and screw them in at the back of the case, but the culprit was the PAL that was not there. Now we could buy them from Tandy of course, but they were so expensive ! So we decided to hire a part-time genius, who bit by bit figured out what that PAL would have to do to connect the bus to that host interface. After several tries, and a lot of time with the guy playing with his locic analyzer, we finally got something. So we got us some empty PAL's and programmed them ourselves. They worked perfect ! And there we went off selling them with our host-interfaces and harddisks for a fraction of the price of Tandy. And of course making a lot of money on it. It didn't get unnoticed by Tandy though, as we sold (a lot) more harddisk expensions then they did. And of course, one day we got some lawyers at the door to shut down our piracy operation. But we didn't pirate anything ! That PAL was our own developement, besides, you can't copy a PAL when the last fuse has been blown out. So we offered that we had our code compared to their code by a third party, and determine if we copied anything. Tandy agreed, and after a short while, we turned out not to have copied anything, our code was not only totally different from theirs, it was more reliable and faster too. From that moment on, we had a pretty good relationship with Tandy, getting serious rebates, and also doing repairs for them that they couln't do themselves. Ah, the days that some clever cowboys could still make some money ... :-)

The Model 4 was my first computer. I remember doing the 128k memory upgrade. It also involved soldering a jumper cable, I was 17 at the time and didn't have a lot of soldering experience. It was kind of terrifying, worrying about frying something with my soldering iron. But it worked, and I had a 128k Model 4. Of course, I really didn't have anything to utilize the extra RAM, but I still felt pretty cool. :)

Thanks for making this video! The TRS-80 Model 4 is my all-time favorite design :)

I love watching you man. Hope I'll find a passion in embedded engineering and programming someday in the future myself ❤

I just bought a Model 4 today, 2017-09-23. So much fun to time warp back to my early youth while playing with it!

This channel deserves way more subs than it has! Really enjoying this.

Excellent presentation. Thank you for putting this video together.

Wow, I remember using this computer in my younger days ... it was so exciting to use at the time, and the floppy disk save/load, etc.

Regarding the lack of shielding on the TRS 80 I and the FCC complaint - in High school where we used them circa 81-82, we would load a game and then set a portable radio up next to the computer set to an AM station (or maybe it was FM - I forget which now), which the signal from the TRS 80 would jam . When ever we "fired" there would be a corresponding sound so we could get some kind of sound effects from the TRS 80 I.

This stuff is sooo simple..That relay was for the cassette interface.

If I remember correctly, J10 is where I plugged in my hi-res board back in the day.

Actually, I believe most of the Radio shacks did have a Model 4 hanging around during the 80's. Before I purchased my own, getting a $2,000 loan from my local bank, I used to go in to the local store and used their Model 4 to write my games. Some times I was there all day till closing time. Back then their receipts were still had written and at the end of the day they, I mean I, used to manually enter the sales receipts into the Model 4 and transmit them over the phone line to Fort Worth TX, the home office.

i worked for Tandy in the 1980's as a manager at a Computer Service Center.. Texas Peripherals drives were sold as after market replacement drives.. Tandy used Shugart or Tandon drives..

I had a Model 4 in 1982, I know because I had it before we moved to a new house. Mine was upgraded to 128 k and three floppy drives, couldn’t afford the hard drive. Mine had the black and white screen. I also had wide dot matrix and daisy wheel printers.

I remember taking first computer lessons with TRS-80 in 1980-1981. Computer lessons were voluntarily then no degree was given to school report

Model 3 and 4 are my favorite!

Tandy also made a sound card that you plugged into the PIO port. It was limited in that it could could play one note at a time. I manage to programed it so it would play the wedding song and a few others.

This is just unbelieveable, just so amazing, I love it! Thank you for this video, I just found one of these computers in my dads room and cant figure out how to use it xD Could you do a video explaining how to use one of these?

I'm still so surprised that the build quality on older computers was crap back in the day compared to today's pc's....they don't build em like they used to...thank heaven...

Very well done video! Thanks for sharing! I worked at radio shack in the mid to late 80's and always wanted one a Model 4. I've been looking on eBay for a while, but can't seem to find one if working or good condition for a reasonable price.

We had these in our high school back in 1990-1991 for a BASIC programing class. ;) Oh the nostalgia. I failed the class by the way. lol! It helps if you don't skip class too much. lol!

Always wanted one after reading Ready Player One.

I had a model 3 for a bit in the 90s

There was a clock you could buy that was NOT Tandy that used a coin cell to power it so it would not loose time. The PIO Time board was made by a company in NY. Same company also made an actual PIO card that would control 16 relays and 16 4N25 inputs. Tandy made a Plug'n'play light controller for the Z-80 Mod 4 that used the cassette as a way to communicate between the light controller and the computer. The funny thing, I, with out knowing what the Peeks and Pokes did, I was able to rewrite their program so to be able to control more then one light at one time to dim, bright or on/off at the same time. X-10 never figured out that might be a desired thing to allow on their own product. As far as I was concerned that was one of the many things that killed the X-10 controllers.

A fluorescent light was used for a timing reference since the power was 60Hz.Us 50Hz Europe. These drives depended on ac line frequency to adjust the timing. Please dont think im being arrogant or bold. I know this old school stuff. You’re doing just fine.

Thanks for sharing! I always wondered what was in one of these. I have a Z80 all-in-one that was yet more expensive, and leaned a lot on the Model 3/4 for styling, but was a very different/better machine inside, the North Star Advantage. Always wondered if it was just a styling copy or whether there were engineering similarities too -- doesn't look like it though.

that 34 pin header is in the location for the hi res card. theres a guy that still makes them his channel is RE1974 and for that extra 64 k of ram it can be used and a virtual disk drive from what ive heard.

Back in the 90s, someone gave me two Model 3s and a Model 4. Wish I still had one of them. I have a Model 100 laptop and a CoCo 2 now. Although all Radio Shack computers had a TRS-80 badge early on, neither is compatible with the TRS-80.

1. U21 (HM6116p-4) is 4016 200NS RAM 2K X 8 Static (U21) and U23 next to it is a MCM68A316E Character Generator (U23) Tandy 8044316 2. J10 is on Page 20 of Model 4 Technical Manual "The graphics connector, J10, contains all of the above interface signals, plus CRTCLK, the dotclock signal, a graphics enable input, and other timing clocks which synchronize the graphics board with the CRTC." 3. the blue "chip at RP4 is Res Pak, 27 ohm, DIP 16-PIN (RP4) 8290027 4. Y1 and Y2 crystals: (pg56 of M4 technical manual) 4.1.5 is your 4Mhz cock. A 4MHz crystal oscillator and a divide by 2 and divide by 4 counter generate the clock signals required by the FDC board. The basic 4MHz oscillator is implemented with two invertors (1/3 of U25) and a quartz crystal (Y1). A 4MHz crystal oscillator and a divide by 2 and divide by 4 counter generate the clock signals required by the FDC board. The basic 4MHz oscillator is implemented with two invertors (1/3 of U25) and a quartz crystal (Y1). A 4MHz crystal oscillator and a divide by 2 and divide by 4 counter generate the clock signals required by the FDC board. The basic 4MHz oscillator is implemented with two invertors (1/3 of U25) and a quartz crystal (Y1). A 4MHz crystal oscillator and a divide by 2 and divide by 4 counter generate the clock signals required by the FDC board. The basic 4MHz oscillator is implemented with two invertors (1/3 of U25) and a quartz crystal (Y1) is the clock A 4MHz crystal oscillator and a divide by 2 and divide by 4 counter generate the clock signals required by the FDC board. The basic 4MHz oscillator is implemented with two invertors (1/3 of U25) and a quartz crystal and on page 27, 3.1.2 Y2 is your crystal for the video

The relay is for the cassette motor control.

11:19 in 1986 creating any document with a dot at the end would mean anything after the dot would be the documents password.

I Brought TRS-80 Model 4 as used I couldn't get it to work I had no boot disks I took it back to store And got my money back now wish I keep it

the Z80 is a great cpu.. I’m not 100% positive but i belive the model 4 could support 2 more floppy drives externally through the internal 34 pin connector…that 2x8k static ram was video memory. Hence the close proximity to the crt controller.

the 6116 is a 2k x 8 static ram

I used these in 7th grade. I hear these use composite video for the monitor display. I wonder if one could hook up a gaming console to this monitor. may have to splice in a connector. I know it's a green screen and games might not look good on it.

The rows of silver pads are a test point for testing in the factory, they never connect to anything user related.

I bet that's a 26-1067 which would have started life as a 16K diskless Model 4. Those are the only M4s which use the M3's dual PSU arrangement.

I didn't know the Apple II used a Z80. I thought it needed a separate Z80 board to run CP/M.

You probably know this, but the CoCo was originally designed as a VideoTex terminal and not a full fledged computer.

It seems the monitor has a rather high refresh rate, it doesn't flicker in front of your camera.

I found it hard to be a "hater" for any of the chips. Z80 had it's big register set and block instructions... 6502 had it's kinda "proto-RISC" thing of not many instructions but loads of speed... I did a little bit of 6800 but, sadly missed out on the 6809.... but that would have been cool too. Oh yeah... actually.... there was one to hate: the 8080 with it's vile ugly assembly syntax which carried on into the 8086, and all the other horrible horrible x86's that we've still got today. Thanks heaven for ARM and ATmega or I'd still be stuck in the 70s wishing I had a Model 3.... a beautiful machine like the one you're taking apart... but better... because "silver!!"

I will never understand why Tandy never used Ziolog support chips for the Z-80 (CTC, DMA, PIO, SIO ect). I am surprise they never made their own Logic Glue for their own boards like commodores did for their computers. It would have saved space on their "mobo'.

The blue chip "RP4" means "Resistor Pack 4".

found the model 4 in the trash few day ago it powers on but just has alot of random numbers on the screen and the orange reset key is stuck down

Black and white, no internal sound, and still that expensive in spite of there being the fantastic Atari 8-Bit family out at the time.

The drive door isn't going to save those disks from the magnetic field created by the CRT and the flyback when the CRT turns on and off. I wouldn't have the disks anywhere near that magnetic-field monster.

I thought the Model 2 used a Motorola 68000, not a Z80 EDIT: I'm wrong, that was the Model 16

That’s not quite accurate. I would frequently use a model 2 with a 8 inch floppy drive. The model 2 was nothing like the model one and was not an upgraded version. It was an entirely diffrent system. One thing you can do is hold down the reset while powering up the computer and bypass the requirement to boot from a floppy drive and boot directly into basic. If I remember correctly.

Ugh, the bodge wires on that board.

Didnt these have a pac man game built in?