Woo hoo - Collection Completed!! TRS-80 inbound

[stephen_usher]

Where did you order your components from?

I've noticed that RS have shifted from using Royal Mail to DPD recently.

[rubber_jonnie]

Where did you order your components from?

I've noticed that RS have shifted from using Royal Mail to DPD recently.

TBH I just got them from eBay, one of my regular sellers. I find the shipping charges for the likes of RS etc to be ridiculous for small items like ICs.

[rubber_jonnie]

Aaaand the parts arrived this morning The replacement IC total so far is 8 74LS ICs, 8 RAM ICs and 2 VRM ICs...

It's all running again nicely now, MEM SIZE? shows up at boot as expected:

PXL_20221005_100110288.jpg (162.37 KiB) Viewed 1588 times

And hitting enter gives me BASIC:

PXL_20221005_100127578.jpg (199.23 KiB) Viewed 1588 times

And as an added bonus, due to the Post Office hoarding our mail over the last few days, these also arrived:

PXL_20221005_101049961.jpg (555.73 KiB) Viewed 1588 times

A bit late for #SEPTANDY, but still pleased, especially as I owned the TRS-80 Level 1 basic manual when I was younger, so a bit of a nostalgia blast.

The next step is to figure out what the next stage for the 64K upgrade is and if I can complete it easily. Also if I can complete it before any more logic ICs die...

[stephen_usher]

[Tomswork]

Very nice repair and clean video.

Tom

[rubber_jonnie]

Very nice repair and clean video.

Tom

Yes, the video is quite nice, I'm just wondering what could go wrong next

[Tomswork]

You never know with these old machines i have a few spare power transistors. For the model and coco machines they seam to be like popcorn

Tom

[rubber_jonnie]

You never know with these old machines i have a few spare power transistors. For the model and coco machines they seam to be like popcorn

Tom

Yep, you can't beat having a few spares

[rubber_jonnie]

So, I've circled back to the 64KB upgrade by Errol Rosser (Remove the .txt from the attached file to get to the PDF) and think I have it figured out - literally.

His 'figure 3' on the 2nd page refers to Z73, where some tracks need cutting and a bodge wire adding. He shows it as a 16 pin IC, but in reality the IC is a 74LS32 - a 14 pin package.

So, some close comparisons made with a photo of the underside of the board, and all you need to do is remove two of the pins in figure 3 and it's correct.

It has been bugging me massively, because I was wondering if he meant Z72 instead which is 16 pin, but no, it's a mistake.

So I think I have the details to carry on, but half expecting it to break again halfway through the process!!

[rubber_jonnie]

Before I crack on with the 64K upgrade, I thought I ought to just run a small 'burn in' to see if all goes well and she behaves before I start mucking around again.

PXL_20221006_084529487.jpg (237.05 KiB) Viewed 1525 times

It's a simple BASIC program that runs a loop of 10000 iterations, generates a random X value between 0 and 127 and a random Y value between 0 and 47, these values representing the 'pixels' you can plot on screen, and turns the pixels on.

Once it's finished the first loop, it does the same again but turns the pixels that have been plotted off, once again using random X & Y coordinates. Essentially it just makes a mess of pixels (Very large ones) on screen and runs until the end of time.

It should give the video RAM a good workout at least and if it all seems to run fine during the day, then I will be cracking on with the upgrade to 64K, hopefully this weekend.