Museum readying a TRS-80 model-1: Difference between revisions

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== Memory ==
== Memory ==


A normal TRS-80 main mother board contains 16K DRAM, and needs and "expansion interface" to add another two banks of 16K DRAM chips for the 48K RAM that BASIC 2 expects.
the previous user probably did not want to buy the very expensive expansion interface and knew that it was possible to replace the uPD4116 16K x 1-bit with uPD4164 64K x 1-bit chips. I knew that this could be done because I have modified dozens of TRS-80 model 1 computers myself in the early 80's. because the uPD4116's use thre different voltages, and the more modern uPD4164's use only +5V, you have to remove some decoupling caps, and wiring .
You can see the patch wiring for this patch from the solder-side of the PCB:
[[File:TRS-80 motherboard TOP side.JPG|1000px]]


One other problem many people opted to address is that the model-1 did not support lowercase letters, the designers chose a spare a few dimes by only using seven M2102 1K x 1-bit static RAM chips for video RAM. So a patch to install the missing RAM chip was quite common, and this user seems to have done the ame thing. the small rectangular PCB seems to indicate this is the case.


A normal TRS-80 main mother board contains 16K DRAM, and needs and "expansion interface" to add another two banks of 16K DRAM chips for the 48K RAM that BASIC 2 expects.
I have not powered up the computer yet, I want to be carefull, and examine the schematics first.
the previous user probably did not want to buy the very expensive expansion interface and knew that it was possible to replace the uPD4116 16K x 1-bit with uPD4164 64K x 1-bit chips. I knew that this could be done because I have modified dozens of TRS-80 model 1 computers myself in the early 80's. because the uPD4116's use thre different voltages, and the more modern uPD4164's use only +5V, you have to remove some decoupling caps, and wring .
I noticed the main +5 TO-03 Voltage regulator seems to have overheated .

Revision as of 22:24, 3 September 2024

Project Museum readying a TRS-80 model 1
Pre-cleaned TRS-80 top.JPG
In 1977 the very first homecomputers came on the market, early in 1977 the Commodore PET 2001, a few months later the Apple 2, and at the end of the year the Tandy Radio Shack the TRS-80 Model 1, the cheapest of the three, and according to many the most useful of the "trinity" as the popular computer magazine Byte called the three in 1995.
Status Initializing
Contact mahjongg
Last Update 2024-09-03


The trinity in the Dutch National video game museum

The NaVGM (National Video Game Museum) in Zoetermeer the Netherlands has a separate room for home computers, and in there you can see (at the moment in August 2024) two of the trinity of computers, namely a PET (Personal Electronic Transactor) model CBM 8032 (this is a later european "business model" with a 80 column screen and 32K RAM, I hope to replace it with a 40 column model that is much better supported with video games, I am the owner of these two PET's) we also have an Apple ][ in a showcase. but we did not have a TRS-80 computer,until now that is. Unfortunately the TRS-80 model 1 we got has earned the name "trash-80". It looked like it has been in a trashcan for at least 30 yes.

The trinity:

Home or Personal Computers from 1977 - Commodore PET 2001, Apple II, TRS-80 Model I, together called 'Trinity77' (edited image).jpg

From left to right the Commodore PET 2001, the Apple ][ and the Tandy TRS-80 model 1.


the filthy model 1: the museum received:

Top:

Pre-cleaned TRS-80 top.JPG

bottom:

Pre-cleanedTRS-80 bottom.JPG

bottom after sticker removal:

Trs-80 after sticker removal bottom.JPG

top after sticker removal:

Trs-80 after sticker removal top.JPG

as can be seen the case needs a re-paint.

I have also opened the computer, and concluded it was extensively upgraded. it seems it was upgraded to 48K of RAM, level 2 basic, and also seemed to have the lower case mod. Also the short keyboard cable was replaced with a long a flexible one.

After re-painting the Case

I re-painted the case, after removing all the stickers and degreasing the case with isopropanol.

I started a applying a grey primer, then after the primer had dried I applied acoating of silver spraypaint, and the result was excellent IMHO.

here you can see the front, not the white spot where the silver paint was completely rubbed off is completely gone. Note the blue stickers that mark that this is a project of mine, and since when it is stored in storage.


TRS-80 painted TOP.JPG

seen from the back you can see that the broken off "rib" is repaired and you can barely notice that it was ever broken off.

TRS-80 back and bottom.JPG

The mother board

looking at the TRS-80 Motherboard you can see that it was extensively repaired and modified. The mother board is mounted inside the case with the components hanging down on the board, so that the keyboard can rest on the bottom of the PCB with some wide round rubber standoffs. One modification that is immediately obvious is that that the short FLEX-PCB connection between the Motherboard amd the keyboard PCB. A known weakness in the design of the TRS-80 is a broken connection cable between the main and keyboard PCB. The previous owner aware of this problem has decided to take drastic actions, and replaced the short and breakabl cable with a much longer and more supple flexcable.

TRS-80 motherboard bottom side.JPG

Memory

A normal TRS-80 main mother board contains 16K DRAM, and needs and "expansion interface" to add another two banks of 16K DRAM chips for the 48K RAM that BASIC 2 expects. the previous user probably did not want to buy the very expensive expansion interface and knew that it was possible to replace the uPD4116 16K x 1-bit with uPD4164 64K x 1-bit chips. I knew that this could be done because I have modified dozens of TRS-80 model 1 computers myself in the early 80's. because the uPD4116's use thre different voltages, and the more modern uPD4164's use only +5V, you have to remove some decoupling caps, and wiring .

You can see the patch wiring for this patch from the solder-side of the PCB:

TRS-80 motherboard TOP side.JPG

One other problem many people opted to address is that the model-1 did not support lowercase letters, the designers chose a spare a few dimes by only using seven M2102 1K x 1-bit static RAM chips for video RAM. So a patch to install the missing RAM chip was quite common, and this user seems to have done the ame thing. the small rectangular PCB seems to indicate this is the case.

I have not powered up the computer yet, I want to be carefull, and examine the schematics first. I noticed the main +5 TO-03 Voltage regulator seems to have overheated .