Quote from: granz on Jan 02, 2026, 09:34 PMThat's the meter that you use to measure lightning - 1.21 jigawatts.   

Thank you, granz for getting it!

Quote from: Chris Savage on Jan 02, 2026, 08:00 PMI can't be the only one to see 121GW and immediately see the connection, am I?!? Please tell me that relates to what I think it relates to.

Quote from: JKnightandKARR on Jan 02, 2026, 08:10 PMAs far as 121GW, NO idea what you mean other then this: https://eevblog.store/products/121gw-multimeter

That's the meter that you use to measure lightning - 1.21 jigawatts.   

Quote from: Chris Savage on Jan 02, 2026, 08:00 PM

Quote from: JKnightandKARR on Jan 02, 2026, 01:44 PM-Output side of D9 = 5v DC and no Hz.

Needless to say, I didn't check anything on R32. Going by that there's a wire on the UK side, I might try the signal inpit wire on that pin, once I locate it..
As for D9 since the freq vanished there and even though theres 5v out, could the diode be the issue or should I just locate the UK straight from Pin 16 and use that??  Obviously the US side is supposed to have a freq of somekind going into the RF box, and my scope shows NOTHING other then the 5v increase. Suggestions? I have seen mods I can buy and have concidered them.

Are there any electrolytic caps inside this unit. Anything over 15 years old, the first thing I do (before ever powering it up) is replace any electrolytic caps. They can leak or dry up and then they no longer work as they're supposed to.

Quote from: JKnightandKARR on Jan 02, 2026, 01:44 PMusing my EEVBlog 121GW DMM and I have the folowing results:

I can't be the only one to see 121GW and immediately see the connection, am I?!? Please tell me that relates to what I think it relates to.

It's got some caps, but none between the ULA and my composite mod. I probed the Z80 and the ULA and they seam to be doing something.

As far as 121GW, NO idea what you mean other then this: https://eevblog.store/products/121gw-multimeter

Quote from: JKnightandKARR on Jan 02, 2026, 01:44 PM-Output side of D9 = 5v DC and no Hz.

Needless to say, I didn't check anything on R32. Going by that there's a wire on the UK side, I might try the signal inpit wire on that pin, once I locate it..
As for D9 since the freq vanished there and even though theres 5v out, could the diode be the issue or should I just locate the UK straight from Pin 16 and use that??  Obviously the US side is supposed to have a freq of somekind going into the RF box, and my scope shows NOTHING other then the 5v increase. Suggestions? I have seen mods I can buy and have concidered them.

Are there any electrolytic caps inside this unit. Anything over 15 years old, the first thing I do (before ever powering it up) is replace any electrolytic caps. They can leak or dry up and then they no longer work as they're supposed to.

Quote from: JKnightandKARR on Jan 02, 2026, 01:44 PMusing my EEVBlog 121GW DMM and I have the folowing results:

I can't be the only one to see 121GW and immediately see the connection, am I?!? Please tell me that relates to what I think it relates to.

https://jknightandkarr.altervista.org/Computers/zx81-schematic-1.png
Well, starting post here on repairing my Timex Sinclair 1000. So here is the schematics. I replaced my NPN transistor, still nothing on the screen at all. I busted out the probes for my GW Instek GOS-620 and probed around aling with using my EEVBlog 121GW DMM and I have the folowing results:
-Tested the transistor with my cheap-o LCR meter, showed good, replaced unknown status NPN.
-Last night, changed the input signal on the composite circuit to the correct wire. I traced, from the ULA pin 16, through D9 and R32 which goes into the RF modulator.
-Hooking the scope to the Pin 16, yielded no results, so I used the 121GW, which has a Hz function, Pin 16, a signal, and 5v DC voltage.
-Input signal wire on mod = nothing, 5v DC and no Hz.
-Input side of D9 = said previous measurments.
-Output side of D9 = 5v DC and no Hz.

Needless to say, I didn't check anything on R32. Going by that there's a wire on the UK side, I might try the signal inpit wire on that pin, once I locate it..
As for D9 since the freq vanished there and even though theres 5v out, could the diode be the issue or should I just locate the UK straight from Pin 16 and use that??  Obviously the US side is supposed to have a freq of somekind going into the RF box, and my scope shows NOTHING other then the 5v increase. Suggestions? I have seen mods I can buy and have concidered them.

Starting thread in Vintage computers..

Quote from: JKnightandKARR on Jan 01, 2026, 08:14 PMIf the ZX80/81 are Z80 based, in theory this could be modicied to work on the ZX80/81.

Yes, and there are several projects that do this. @ikjordan has a GitHub page (https://github.com/ikjordan/picozx81?tab=readme-ov-file) with one. His (hers?) works on several platforms, one of which is less than $25 from Pimoroni (https://www.pishop.us/product/pimoroni-pico-vga-demo-base.)

But, if you let go of the ZX-81 format, and just use a serial terminal on your PC, you can get full Z-80 experience from just the Pico, a breadboard, a micro-USB cable and some hook-up wires (and optionally an SD card socket.) Of course, you won't get the single-key BASIC, the low-rez graphics nor the ZX gaming experiences with these projects. You also won't have a true Z-80 hardware system - but if that is not so important, these projects will be cheaper.

Quote from: Chris Savage on Dec 31, 2025, 09:05 AMI'm considering building something like this as a quick / cheap way to get people familiar with Z80 programming.

Z80 Emulator for Raspberry Pi Pico and other RP2040 based MCU boards

It could run on this $4.00 Raspberry Pi Pico RP2040 from Adafruit.

If the ZX80/81 are Z80 based, in theory this could be modicied to work on the ZX80/81.

Quote from: granz on Jan 01, 2026, 08:04 AM

Quote from: JKnightandKARR on Dec 31, 2025, 01:04 PMI do not. Is there a way to hook them up to the system or something?

I don't know what you mean by hook them up to the system or something. The Raspberry Pi is a system in itself. If you just load the Pi OS, with the changes mentioned in those links above, the Pi will give the desktop video out on the composite pins/RCA socket. You plug that into your monitor/television to verify that the monitor works. That will give you the something with a known good signal for verification that Chris mentioned.

Quote from: Chris Savage on Dec 30, 2025, 11:09 PM

Quote from: JKnightandKARR on Dec 30, 2025, 10:18 PMSo either A)The systems so far don't work and have to be repaired, or B) Even though my TV has a coax jack, it DON'T like the systems at all...  Guess I could try them through my VCR on my other tv...

Too bad you don't have something with a known good signal for verification.

I didn't know if someone had one of those Pi's to change video, but i know what you mean now. Lol I got a Nintendo Wii hooked up to my tv right now, so I know the composite works. Off next 2, so tonight, I'll break out a scope n probe inside to see what I can find.

I was thinking this would provide an easier path to messing around with the Z80 using modern hardware. While I don't have the time to explore it at the moment, I would be happy to fund such an endeavor, should someone want to pursue it. It could then be duplicated to open the door to others as well.