Quote from: Chris Savage on Jan 09, 2026, 03:45 PM

Quote from: JKnightandKARR on Jan 09, 2026, 12:50 PMYeah, but the Pin 11 reading dmm vs scope confuses me.... maybe retest later with diff meter.. on the heat thing. I think I'll upgrade that 7805 to the upgraded part... burnt myself last night.

As an electrician who has worked with high voltages, there's a principle called, "LIVE-DEAD-LIVE" testing. It's a way to confirm that a circuit is shut down and safe to work on. What if you were working on 480VAC and your meter measured no voltage? You might work on the circuit and it may actually be live, but perhaps your meter had a blown fuse or bad probe / lead. Using a proving unit, you prove that the meter can detect 480VAC, then you check the circuit under test, then you check the proving unit again to confirm the meter is working. Safety first.

But at lower voltages, you can use this same principle to confirm that the meter is working properly. In your case you weren't detecting voltage at the CPU pin, but the question is, could you detect voltage using that same meter from other points? One of my power supplies has lugs with multiple voltages at the outputs (3.3V, 5V, 9V, 12V) and I will often confirm voltages at these posts before testing a circuit.

The meter is fine along with probes. I probed multiple spots n got readings from them, just not much from there, and that was after the DC and AC measurments. Infact, pin 11 came before pin 6.

Quote from: JKnightandKARR on Jan 09, 2026, 12:50 PMYeah, but the Pin 11 reading dmm vs scope confuses me.... maybe retest later with diff meter.. on the heat thing. I think I'll upgrade that 7805 to the upgraded part... burnt myself last night.

As an electrician who has worked with high voltages, there's a principle called, "LIVE-DEAD-LIVE" testing. It's a way to confirm that a circuit is shut down and safe to work on. What if you were working on 480VAC and your meter measured no voltage? You might work on the circuit and it may actually be live, but perhaps your meter had a blown fuse or bad probe / lead. Using a proving unit, you prove that the meter can detect 480VAC, then you check the circuit under test, then you check the proving unit again to confirm the meter is working. Safety first.

But at lower voltages, you can use this same principle to confirm that the meter is working properly. In your case you weren't detecting voltage at the CPU pin, but the question is, could you detect voltage using that same meter from other points? One of my power supplies has lugs with multiple voltages at the outputs (3.3V, 5V, 9V, 12V) and I will often confirm voltages at these posts before testing a circuit.

Quote from: Chris Savage on Jan 09, 2026, 09:11 AMWell, I mean your 5V, Φ and /M1 signals look good. So it would seem the Z80 is running.

Yeah, but the Pin 11 reading dmm vs scope confuses me.... maybe retest later with diff meter.. on the heat thing. I think I'll upgrade that 7805 to the upgraded part... burnt myself last night.

Well, I mean your 5V, Φ and /M1 signals look good. So it would seem the Z80 is running.

https://jknightandkarr.altervista.org/Computers/PowerSupply.jpg
Power Supply at the jack.


https://jknightandkarr.altervista.org/Computers/5v_card.jpg
5V @ the card edge connector. Verified, 5v


https://jknightandkarr.altervista.org/Computers/9v_A.jpg

https://jknightandkarr.altervista.org/Computers/9V_B.jpg
Couple of shots of the 9V at the card edge connector. Kinda messy..


https://jknightandkarr.altervista.org/Computers/M1.jpg
M1 at the card edge connector. Freq = 810 Khz.


https://jknightandkarr.altervista.org/Computers/Pin6.jpg
Pin 6. 3.25 Mhz


https://jknightandkarr.altervista.org/Computers/Pin11.jpg

https://jknightandkarr.altervista.org/Computers/PIN11_scope.jpg
Pin 11 DMM Vs Scope.... UNKNOWN why meter voltage is diff from the Scope measure, which was 5v..... DMM showed no AC voltage.


https://jknightandkarr.altervista.org/Computers/7805.jpg
Temp at the voltage regulator


https://jknightandkarr.altervista.org/Computers/Z80.jpg
Z80 Temp

https://github.com/ikjordan/picozx81?tab=readme-ov-file
I did find this, which does involves multiple platforms one of which is the Raspberry Pi Pico. If I make one of these, might try n add the expansion port.

Quote from: Chris Savage on Jan 07, 2026, 02:35 PM

Quote from: JKnightandKARR on Jan 07, 2026, 01:45 PMAnother schematic

I wanted to go over what I covered on the phone so when you reply with your findings, people aren't confused. I previously mentioned replacing ALL electrolytic caps in the system. But in today's conversation I mentioned the following next steps to confirm functionality:

• Verify DC voltage at the Z80 CPU (PIN 11) using your multimeter on DC voltage. Should be ~5.0VDC and then switch to AC to measure any ripple voltage, looking for excessive noise.
• Verify the clock pulse at PIN 6 on the Z80 CPU. By using a digital scope you can see the waveform and measure the frequency at the same time, which should be ~3.25MHz.
• Verify the output of the /M1 line on the Z80 CPU (PIN 27). By using a digital scope you can see the waveform and measure the frequency. The /M1 line should have activity if the Z80 CPU is executing instructions.

Many digital scopes have a USB port which can be used for screenshots of what you're measuring. If you can do this for the clock and /M1 signals, please post them for analysis.

Thanks Chris, will do!

Quote from: JKnightandKARR on Jan 07, 2026, 01:45 PMAnother schematic

I wanted to go over what I covered on the phone so when you reply with your findings, people aren't confused. I previously mentioned replacing ALL electrolytic caps in the system. But in today's conversation I mentioned the following next steps to confirm functionality:

• Verify DC voltage at the Z80 CPU (PIN 11) using your multimeter on DC voltage. Should be ~5.0VDC and then switch to AC to measure any ripple voltage, looking for excessive noise.
• Verify the clock pulse at PIN 6 on the Z80 CPU. By using a digital scope you can see the waveform and measure the frequency at the same time, which should be ~3.25MHz.
• Verify the output of the /M1 line on the Z80 CPU (PIN 27). By using a digital scope you can see the waveform and measure the frequency. The /M1 line should have activity if the Z80 CPU is executing instructions.

Many digital scopes have a USB port which can be used for screenshots of what you're measuring. If you can do this for the clock and /M1 signals, please post them for analysis.

https://jknightandkarr.altervista.org/Computers/VISTA_Newsletter_v3_n5_OCR.pdf
Another schematic

Quote from: Chris Savage on Jan 06, 2026, 07:18 PMSince we have several cat lovers in the family, I also made these as kind of a gag gift for a few people.

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Rotflmao thats funny!