Was throwing out an old PC and saw this in the ewaste bin. Charger sitting right next to it. Got it home, popped some batteries in and it fired right up. Not a thing wrong with it from what I've seen. I've tried using my esp32 zimodem and it doesn't seem to connect like on my model 100 but commands work otherwise and this thing is almost spotless
This is a TRS-80 MC-10 with the Pi-Key expansion mod installed. It adds support for a USB keyboard and two 9-pin joystick ports (or Genesis controllers, if you're feeling fancy). It sets the whole computer up like a tower with the stand. Folks seemed to have a pretty good time playing around with it, and the MC-10 port of Pac Man is really quite good.
So I picked up a pair of TRS-80 Model 100s (Both were said to work, one does, one doesn't, I haven't gotten to debugging the broken one yet). Both included this weird floppy drive system. My googling has failed me, anyone know anything about them? Are they worth anything to anyone?
The seller also included these hard drive things, I'm not even sure if they actually go with the TRS80. Same question here, are they of any value to anyone? How would you even use these?
Thanks for your help!!
I plugged up a Model 3 board I had from another parts machine. The CRT and video circuit seem fine on the model 4 chassis. The Model 3 seems to just give garbled text. One of the transparent ribbon cables seems in really bad shape (falling apart). I would also like to fix this.
As far as the Model 4 motherboard there is no video signal although my oscilloscope shows some weak signals for h / v and maybe video. Using a pretty janks scope atm. the H and V seem strong the video seems weak. i get a nice puls off the middle pin. (not shown).
Any help appreciated getting these in working order. I can now confirm it is a mainboard issue on the 4.
Bought a game for the trs-80 before I realized "how am i going to run this?" Is there some way to turn it into an audio file to play back to the cassette port?
I plugged my model III motherboard (pictured here) with a power supply from a model 4 into the position labeled 1.
Result: I get garbled text and the keyboard fails to respond. The reset button does not work (even though it passes a continuity test). Text seems to ghost write itself and then halts.
Question 1: Do I need power at "2" (5 pin adapter) to test this board?
Question 2: Is there a manual way to reset the board without the button?
My model 4 power supply does not have the right pinout (it has a 5 pin but colors look in wrong position) . I have a power supply for a III but it makes crackly noise and I havent recapped it yet.
Question 3: What is the bear minimum to test this board?
Hey all,
I recently acquired a TRS80 model 100 that was sold as non working in perfect cosmetic condition. I was originally going to design an stm32 based motherboard replacement for it, but when seeing just how *mint* it actually is i decided to give a shot at fixing it, only gutting the motherboard if it's a no-fix.
This is the device:
It came with a bit of corrosion on the DC jack, nothing major.
The actual failure mode reported by the original owner was that they had bought this as a working unit, they did some work on it, clearly caps got replaced, the memory battery is also new. It seems like they taught the LCD failure would be fixed by a cap swap, it was not. They then threw in the towel and sold it for fairly cheap as dead.
The keyboard on this thing is honestly one of the best ones i have ever had the pleasure to type on, it's miles ahead of the Amstrad ones i've touched before.
When i got it and plugged it into my lab psu, i got 60mA at 6V, which i believe is within expectations for this device? I got the described LCD issue where a "blot" appears at boot, flickers a bit, then disappears leaving the LCD blank.
I've probed around the PCB, the 5V rail reads as 5.1V, the negative LCD bias is present on the motherboard at around -4.5V, at C85 it reads as -6.524 V. The CPU clock (X2) is active with a 4.91 MHz oscillation, T21 (DC/DC) runs at 151 kHz with a roughly 18V pkp waveform.
So all of these indicators looked healthy (to someone who isn't that well versed in this specific hw). I probed the system bus and noticed it was held down completely dead right after the first ALE pulse. I noticed an option ROM chip in the bottom socket and removed it, this solved the system bus being dead and showed activity on all addr / data pins, the LCD interface also got signals at this point, however still the exact same LCD symptoms remained (though now the speaker had a somewhat audible pop at boot).
At this point i'm probing for further regulator issues and instabilities, but i'm also looking at the 24K of ram (3x8K) as potentially bad, since this seems to be a common theme with these machines. If anyone has any bright ideas on what might actually have gone wrong with this specific device, feel free to participate.
If i can't fix this in a reasonable way i'll just move onto designing my motherboard and i'll keep the old one in a closet i guess, i've looked at building custom ram modules, they seem like they'll cost more than the price of the machine, but if i can get definitive proof that it's the ram i might try that.
Pictures of the interior:
