Help with troubleshooting: Zed Pro

[Iain Tatch]

Hello

Another day, another newbie looking for a little troubleshooting help I'm afraid.

I've recently bought & assembled a Zed Pro. But I'm getting nothing when connecting to the terminal interface.

What I've tried:

The troubleshooting guides are very helpful, thank you to whoever wrote them. There was a pause a few days ago while I waited for a delivery of a logic probe to arrive, and once I had that I was able to get a bit more detail.

Once powered up & reset, the pins are outputting as I'd expect for the RomWBW logic probe table with the very important exception of all 8 data pins. Those seem to contain no signal at all, which is somewhat concerning.

Things I'm fairly happy are correct:

• Backplane. I've painstakingly walked over all connections with a mutimeter and all pins are, to the best of my ability to confirm, connected correctly with no shorts
• Z80 module. Removing the CPU and again using a multimeter to confirm a good connection between each DIL socket pin and the associated pin on the board. Incidentally, how crazy is the pin arrangement on the Z80? It really makes you appreciate the effort involved in creating a sensible ordering on the backplane.
• Dual clock module. I pulled this from the board, fed in +5V directly, set the clock 1 jumper to "slow" and attached my cheap Sparkfun logic analyzer to the clock pin, where I saw a nice regular signal. (I don't have an oscilloscope so the higher frequencies are out of reach for analysis, but I assume if it works on one frequency it will multiply up/down just fine).

So my efforts are being concentrated on the SIO/2 board and the 512k ROM/RAM board. Of course those two are among the more complex boards in terms of assembly as well as functionality, and I'm a little stuck for how I might begin to troubleshoot problems with either of them.

Any suggestions will be gratefully received. I'm of course happy to provide any pictures or other information that might help someone help me out.

Thanks loads in advance

Iain.

[Spencer Owen]

Hi Iain,

Just a very quick reply as I am currently in Liverpool for MakeFest, but I just saw this and wanted to make some suggestions.

You say that there is no activity on the data lines. That's the bit I would be concerned about. Are they all high? All low? Or fixed on a particular pattern?

If you remove the ROM/RAM module do they do anything?

I would suggest building a simple NOP generator using just the clock and CPU module and pulling all the data lines high. You should then see the address lines counting up in binary (each line half the frequency of the previous one) which should then confirm that the CPU is running.

Spencer 

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[Willy De la Court]

Spencer NOP should be all low on the datalines not HIGH.

[Spencer Owen]

Sorry. Yes, you're quite right. That'll teach me to post a quick reply from my mobile without thinking first :-)

Spencer 

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[Iain Tatch]

Thanks very much Spencer.

> You say that there is no activity on the data lines. That's the bit I would be concerned about. Are they all high? All low? Or fixed on a particular pattern?

Literally nothing. Poking at those pins with my logic probe it registers neither high nor low. Having written that down just now it occurs to me I should see what the multimeter says for those in terms of voltage.

> I would suggest building a simple NOP generator using just the clock and CPU module and pulling all the data lines high. You should then see the address lines counting up in binary (each line half the frequency of the previous one) which should then confirm that the CPU is running.

I did this (pulling them low of course as another contributor mentioned) and saw exactly the pattern mentioned. So there seems to be no issue with the Z80 board at least.

Iain.