TRS-80 Coco model 1 repair Model 26-3002

[VERAULT]

This just keeps getting less and less attainable. I heard some folks got Coco-2 keyboards (that is what I think this is) working on the coco-1. Well you see the outer bezel around the keys. It looks like the same size keyboard area on the Coco-1 but its acually wider. This wont fit in the hole for the keyboard on my Coco-1.

So Im at a loss. This really stinks

 

[ACK]

This just keeps getting less and less attainable. I heard some folks got Coco-2 keyboards (that is what I think this is) working on the coco-1. Well you see the outer bezel around the keys. It looks like the same size keyboard area on the Coco-1 but its acually wider. This wont fit in the hole for the keyboard on my Coco-1.

So Im at a loss. This really stinks

Maybe one of the chicklet keyboards models will show up on Ebay cheap enough. I''ll keep an eye out for ya.

 

[VERAULT]

I certainly hope so. iHave been sending out feelers all over and keeping my eyes out.

 

[VERAULT]

Ok I have a keyboard for a Coco 1 . And I have updates but first I need help. Why would the keyboard work on another coco 1 but not work at all on my Coco 1? Could my machine have another fault? What would cause the KB not to work?

 

[VERAULT]

I guess I should just check the obvious huh? I found my PDF of the Original COCO service manual and I didnt hold out much hope as all it had listed under KB troubleshooting was:



Gotta love Radio shack.. U8 was bad! Now do I have a spare? I bought this kit: https://www.ebay.com/itm/113539027035 in early oct and says its included. Now where did I put those ICS?
Will post back tomorrow.

 

[VERAULT]

ok Ill break this update into a couple posts so its not too long and borring (or in my case rambling).
As for the last post The U8 Motorola MC6821P IC was bad as the keyboard wouldnt work. I swapped it with another to test. And the KB was working again. I bought those COCO chips in that ebay listing on the last thread and it had a hitachi equivalent so thats what I ended up replacing it with.

EDIT!!:: Whats the difference between U4 and U8 as they both seem to be the same type of IC?!


So I havent yet made a disk image so I cant run diagnostics but so far I have had to replace U8. U2 and U10 were missing so I had to purchase them online. U19 was smashed off so I tacked it back on(transistor is good). U29 was inserted with one leg out of the socket and making contact with the RF shield cage (IC is good). U9, U14, and U15 had very corroded legs and dirty sockets which were all cleaned and now working. One 4116 RAM IC was bad. All the glass capacitors above the ram sockets had one leg desoldered so they were tested and resoldered in place. Of course the power cable was cut and a new one ws fitted in.

So the computer was missing a keyboard and the reset switch was broken. Now looking back at everything, I went in with ambition but I can see this system was a complete basket case!

Well I have a working keyboard and a replacement reset switch. Where did I get them. So I put out feelers all over the internet for a keyboard. The best I could get was a COCO2 keyboard which just does not fit unfortunately but nothing else. Recently a COCO 1 showed up on shopgoodwill. The price? Fair at best I guess when the auction was over. I paid. They mailed it to me.. And you know the drill. They put it in a box the same size as the computer and this happened:



The entire Bottom plastics are shattered really and cannot be saved. This is the first time I have bought something from Shopgoodwill and had it arrive badly packed. Granted I havent bought anything from them in the past couple years since they have become popular. I filed a claim and got my money back.

I tested out the board and it seems to work. Its got the 1.1 version of BASIC as opposed to my earlier 1.0 on the swapmeet machine I am repairing. Its also got a version "Mainboard" and the version on my earlier swapmeet model is a "D"


And just for reference the Swapmeet early model info is below:

 

[VERAULT]

The REV "E" board from shopgoodwill also had a HIGH/LOW jumper that was not on my earlier REV "D" swapmeet board. Whats it for?


So I feel bad sacrificing one good Coco to save another. But in truth, it wasnt me who destroyed this model it was Shopgoodwill. I can save the top cover, psu, and board (once I get a replacement reset switch since I took that switch for my other unit)

I cant feel bad, these things are getting thrown in the dump all the time and I didnt pack it badly. ITs parts will live on somewhere else.



I also took the RF shield and PSU shield to add to the Swapmeet Coco


Now its finally time to test out my FD-502 floppy drive and controller. And with just a little cleaning it works fine. Although there appears to be dried plumbers putty (or something the same color and consistency of) all over the back and bottom of the drive enclosure and the controller cartridge. The only thing that takes it off is scotchbrite but it takes the paint too.

I formatted a disk, rebooted, made a small basic program, saved to disk, DIR the disk. and Ran from the disk. IT works great!

However its reporting only 6439K available when the Floppy controller is inserted and 8480 when its not. Seems low even for color basic but what do I know?

EDIT!::: IS there any advantage to burning a new updated ROM into this system?


Strangely the shopgoodwill machine if you look at the last post is reporting 14631 free without the disk controller. That seems way too high even for a slightly newer ROM. Am I wrong? These are supposed to be both 16KB machines.

Here is the system all back together


Oh yes I forgot to mention. I swapped the decals from the swapgoodwill case as the ones from the swapmeet were severely weathered (did not swap plastics)

I also decided to try out my 26-3024 multipak interface. It is in white as it came with my COCO 2 but it is in working order, it just needs a cleaning. I only have one cart at the moment, "Personal Finance II" which came with the SD-502 floppy drive purchase. Nice program, too bad it only works with saving and loading from cassette.


So thats it in a nushell. Came a long way but we got there. I reached out to Ed Snider about buying a COCO SDC but I never heard back. I want to get into making real floppies. I am hoping I can do that with the COCO SDC and the SD-502 floppy in tandom. I have no idea. Maybe you guys can tell me methods for easily making coco disks.

Thats it for now.

Mick

 

[grimm]

That is looking good. The high/low jumper is for the 32K model, the early ones had 64Kbit memory with either high address or low address bad memory. The jumper was used to select which address space to use. The later ones had all good memory and there were some hacks to up the total memory to 64K. Too bad about the damage, it's always sad.

Jason

 

[VERAULT]

Thank you! Really looking forward to getting much more into the Coco system. Seems to be an Island unto itself.

So on the earlier models how did they set which part of the 64Kbit ram chips were bad? I guess maybe they only bought a certain type??

 

[ACK]

Congratulations on finding another computer with a chicklet keyboard! Sucks that it was packaged so badly. At least all those parts left working are being used to revive yours. Thanks for taking us along for the journey.

 

[grimm]

Thank you! Really looking forward to getting much more into the Coco system. Seems to be an Island unto itself.

So on the earlier models how did they set which part of the 64Kbit ram chips were bad? I guess maybe they only bought a certain type??

I'm not sure, but I assume that they tested them. They would need 8 of the same type for it to work. I did test mine and changing the jumper didn't do anything, so I think I must have the fully good chips?

 

[VERAULT]

So I got another problem on this Coco 1. While troubleshooting my Dragon 32 Universal joystick adapter on my coco 1 and coco 2 I discovered a new fault on the Coco1
Whenever I type the letter "O" I always get "OH"

Now what?! is the U8 MC6821P faulty again?