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#1
06-18-2008, 03:09 PM
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Thanks, I'll do some troubleshooting tonight when I arrive home. I remember that my incoming 16 volts from the PSU is more like 14.7. I could also try tweaking it closer to the speced 16 volts.
I noticed that yours was over 16 volts. 
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#2
06-18-2008, 07:53 PM
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Ok, I knew I wasn't (completely) crazy. You can run the front panel without the CPU, but you have to pull BA (CPU pin 7) high. I removed my 6800 and connected CPU pin 7 to pin 4 (IRQ) which is tied high through a 3.3k resistor, and my front panel works fine.
Does anyone know why it worked for me once and then stopped? BA is driven through CMOS buffer PP, can a CMOS buffer whose input is floating drive its output high some times and low other times, at random? Geoff.
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#3
06-18-2008, 08:30 PM
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I followed your lead in a different way. I plugged the 6800 cpu directly into the motherboard without the 32k expansion. All symptoms dissappeared, and it runs fine. So, its something with the cpu to expansion BRD connection, expansion BRD to motherboard connection, or some other problem with the expansion card. I need to leave home again, but I'll continue this evening. Any other thoughts based on this new info? I was carefull about seeing the pins making contact to the socket in the motherboard.
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#4
06-18-2008, 11:18 PM
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Well that's encouraging. Unfortunately, I don't have a memory expansion board, so I'm not going to be much help there. Maybe Grant will have some suggestions when he logs in.
Geoff.
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#5
06-18-2008, 11:57 PM
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The board works by installing the cpu into its socket. Then the mini board has through connectors on the bottom that plug into the original cpu socket on the motherboard. If I am reading the info correctly, I have identified that pin 34 does not make the connection through the socket into the motherboard by using my meter. This would be easy to fix. Of course I need to confirm that this isn't by design. I'm reading the schematics to try and determine. I'm sure Grant will be able to confirm.
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#6
06-19-2008, 12:05 AM
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Ah yes, that would be a Bad Thing. That's the Read/Write line from the CPU. I don't see anything on the circuit diagram that's not meant to pass through to the motherboard.
Geoff.
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#7
06-19-2008, 02:16 AM
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All that effort and I'm almost embarrased to say what the solution was. The socket into the motherboard from the mini 32k wasn't seated enough. The trouble is that you can't see the pins make contact very well because there is almost no clearance (Grant says this in the instructions). But, I had to use way more force to get a good seating than I'm usually comfortable with. Advice to anyone else, install the mini-expansion with the motherboard on a flat surface outside of the case.
What do they say? The obvious answer is usually the correct one? The front panel and the terminal seem to be working perfectly. Thanks Geoff, you led me in the direction of the CPU, which was the correct focus area.
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#8
06-19-2008, 10:50 AM
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Great. And congratulations on getting it running. It's a fun little machine, isn't it?
Geoff.
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#9
06-19-2008, 08:11 PM
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Quote:
The R/W line does not go directly from the 6800 to the motherboard. The GAL decodes the address. If the 6800 wants to READ from the flash or sram, then it puts the external Altair 680 bus in a WRITE mode. If it was in a read mode, then the data buffers from the expansion card memory and the 680 motherboard buffers would clash!  I know that isn't the cause of the problem here, I just wanted to explain it...
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#10
06-19-2008, 08:42 PM
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Quote:
Geoff. Last edited by Geoff Harrison; 06-20-2008 at 01:40 AM.
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Hybrid Mode
