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Anyone know what this mod board is? TRS-80 Model 1

Thank you. I got four of these machines that came out of a school district in Montana. Apparently they were all hooked together through a switch box to a tape recorder so all the students could share it.
 
The Later ROM (Ver 1.3) improved the Cassette Interface along with less keybounce problems.
I upgraded my Model 1 Version D to ROM version 1.3 and A KSG Tech Lower Case Modification.


Larry
 
Yeah, IIRc that mod was actually a factory mod, not something added by users. My Japanese TRS-80 Model I has it, or something very similar.
 
cjs said:
Yeah, IIRc that mod was actually a factory mod, not something added by users. My Japanese TRS-80 Model I has it, or something very similar.
Click to expand...

The schematic for it appeared in several TRS-80 magazines, presumably for use by people who’d made so many Homebrew mods to their machines they were afraid to let Radio Shack touch their machines, but yes, it was generally a factory fix or applied by a Radio Shack service center to older machines when:

A: customers complained hard enough or

B: when Level I models were upgraded to Level II

There are several different variants of it, so the exact shape/size of the board might be different on any given machine.

Per @ldkraemer’s comment, it’s basically a crude one-shot circuit that briefly “locks out” signal input after a pulse is detected. This is to work around a software bug in the cassette input routine, and it’s actually kind of a PITA in certain circumstances, but apparently this hack was a cheaper fix than paying for new ROMs.

The final version of Level II basic fixes the routine, rendering it unnecessary. There was an 80 Micro article that said you could identify Model Is with the fix at a glance because they came with a sculpted Alps keyboard instead of the “stair-stepped” Hi-Tek all the older Model Is have, but I have no idea if those two changes actually always came hand-in-hand,
 
Four machines here, all Alps keyboards.

Thanks for all the info. Back when these came out my high school got a grant to buy either a Model one or a Commodore PET. We ended up with an original PET and I never got any time on a model one until today.
 
Three of the four machines just worked except for a few dirty key switches. So they must have been fairly reliable computers. Especially given a school environment.
 
Yes, the biggest problem is from the Power Brick not being on a switched Hot. They heat up
and self destruct over time. I had mine on a power Strip.

Larry
 
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