How likley is radiation poisoning if I turn on the computer with the case off?
Nil. The only thing in that computer that’s producing meaningful amounts of radiation is the CRT (which produces X-rays), and they’re all pointed at your face, so it has special glass to block the X-rays before they’re emitted.
The power supply has high voltages that can kill you, as does the display circuitry. Those voltages should be more or less covered up, but be careful what you touch in the power supply and on the boards connected to the CRT. The logic board is unlikely to contain anything particularly dangerous. The plastic packages on the memory (and other) ICs are completely safe.
Yes, don’t touch the tube or anything near the tube. An old electrician’s trick is to work with one hand in your pocket: it’s safer.
Okay, Just wondering what parts not to touch
That’s unlikely. Virtually no microcomputers can actually detect whether a cassette recorder is connected or not; they simply send signals out and read signals from the pins, and whatever happens on the other end is not their problem.
I know that this is a kind of old thread, but hopefully this will help:
The “Model 3 Service Manual” can be found on the Internet Archive (https://ia903008.us.archive.org/8/items/RadioShackTRS80ModelIIIServiceManual/Radio%20Shack%20TRS-80%20Model%20III%20Service%20Manual.pdf)
Mods, if this violates aging policy, please accept my apologies, and you may delete this.
Thanks for the link! I guess, even if it were to come too late for the occasion, it may be still a useful resource for anyone trouble shooting their Model 3 (and finding this thread in need for information.)
One thought could be to replace your Z80 with my MCLZ8 and mirror the RAM and ROM inside of the microcontroller on this board, running them cycle-accurate. For debugging purposes it could demonstrate if the problem is within the motherboard’s RAM, ROM or their chip select logic which is a good number of chips. Assuming this works, we can then isolate the problem to specific bits, bytes, or components using peeks and pokes display results to the host PC over the USB UART.
This may seem a bit complicated… but in actuality it is probably less complicated than debugging the vintage digital logic with oscilloscopes or probes you may not have, or as expensive as shipping it to and from someone else who can fix it. :). All you need is a Teensy 4.1 which is $30 and one of my MCLZ8 boards which I can send for shipping cost only. (while supplies last)