Almost Up 'n Running and now a Step Back ...

[Walt Perko]

Hi, 

In  the ZAltair mini-FP computer:  

mini-Front Panel board

TDL ZPU board

FlexRAM board

88-2SIOR1 board

ESP32 FDC+ module

The yesterday I was able to BOOT the ZAltair mini-FP computer to the AltMon prompt.  

I should have ran the RAM test, but I didn't assuming the FlexRAM board was working 100%.  

Today after soldering a pair of wires to the LM7805 GND and 5V OUT to power the ESP32 FDC+ module and ReInstalling the 88-2SIOR1 board and ESP32 FDC+ module I can't get the computer to BOOT to AltMon or the Serial CP/M ... 

Today I tried entering KILLABIT via the front panel switches, but found as some addresses like 020octal to a few more addresses up from there I couldn't get any pattern to DEPOSITE ... 

With that, I swapped out the FlexRAM board to different FlexRAM board ... same problem trying to DEPOSITE to some addresses ... 

I'm thinking the problem might be something on the mini-Front Panel board.  

  

  

I took a few photos as I was trying stuff with the computer ... 

Before Power ON:  

After Power ON and STOP+RESET ... I'm not sure the 88-2SIOR1 board should be showing four RED LEDs ??? 

.

[Patrick Linstruth]

I would start with undoing your modification and see if the problem goes away.

On Aug 15, 2025, at 9:06 PM, Walt Perko <r4r...@gmail.com> wrote:

Hi, 

In  the ZAltair mini-FP computer:  

mini-Front Panel board

TDL ZPU board

FlexRAM board

88-2SIOR1 board

ESP32 FDC+ module

The yesterday I was able to BOOT the ZAltair mini-FP computer to the AltMon prompt.  

I should have ran the RAM test, but I didn't assuming the FlexRAM board was working 100%.  

Today after soldering a pair of wires to the LM7805 GND and 5V OUT to power the ESP32 FDC+ module and ReInstalling the 88-2SIOR1 board and ESP32 FDC+ module I can't get the computer to BOOT to AltMon or the Serial CP/M ... 

Today I tried entering KILLABIT via the front panel switches, but found as some addresses like 020octal to a few more addresses up from there I couldn't get any pattern to DEPOSITE ... 

With that, I swapped out the FlexRAM board to different FlexRAM board ... same problem trying to DEPOSITE to some addresses ... 

I'm thinking the problem might be something on the mini-Front Panel board.  

<20241231-ZAiltair mini-FP Front panel-c2K.jpg>

<20230729-TDL ZPU Lyndon Bradish Top-Rc2K.jpg>

<20250811-ZAltair mini-Front Panel FlexRAM-R2K.jpg>  

<20250811-ZAltair mini-Front Panel 88-2SIOR1 SN 0026-R2K.jpg>  

I took a few photos as I was trying stuff with the computer ... 

Before Power ON:  

<IMG_8996-IMSAI-JAIR 8802SIOR1 LEDs-c2K.JPG>

After Power ON and STOP+RESET ... I'm not sure the 88-2SIOR1 board should be showing four RED LEDs ??? 

<IMG_8997-20250815-ZAltair mini-FP  8802SIOR1 LEDs-c2K.JPG>

.

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<20250811-ZAltair mini-Front Panel 88-2SIOR1 SN 0026-R2K.jpg><IMG_8997-20250815-ZAltair mini-FP  8802SIOR1 LEDs-c2K.JPG><20241231-ZAiltair mini-FP Front panel-c2K.jpg><20250811-ZAltair mini-Front Panel FlexRAM-R2K.jpg><IMG_8996-IMSAI-JAIR 8802SIOR1 LEDs-c2K.JPG><20230729-TDL ZPU Lyndon Bradish Top-Rc2K.jpg>

[Walt Perko]

Hi, 

Okay, I pulled the 88-2SIOR1 board (the modification is just the +5V and GND) wire to the ESP32 FDC+ module (BTW, when computer power comes ON, I can see the ESP32 FDC+ module cycle through the four disk drive LEDs as normal.)  

After pulling the  88-2SIOR1 board now there is only the mini-FP, the TDL ZPU and FlexRAM board in the computer.  

I started with the simplest little program I can toggle-IN on the front panel switches  "RAM ZERO":   063octal and 307octal    Running the program for a couple of seconds it normally puts 00000000 into all but the initial few bytes of RAM.  

Running this test, I'm seeing 00000010 in all the RAM ??? something is wrong somewhere.  

I swapped out the TDL ZPU board for another TDL ZPU board and I'm getting the exact same results!  

I then swapped out the TDL ZPU for a Cromemco ZPU and the initial  "RAM ZERO"  ... the program worked perfectly.  

Then I started to toggle-IN the KILLABIT program and noticed that the first DEPOSIT didn't deposit!  I had noticed that before a few times, but thought it was my fat fingers rather than the computer, but now I see it's the computer.  For some reason I need to DEPOSIT NEXT the 2nd BYTE of any program, then RESET or EXAMINE 0 to DEPOSIT a byte into address 0 ... 

I'm guessing that's a chip on the mini-FP board.  

I got KILLABIT toggled-IN and it's working as it should, so now I know I have some compatibility problems or faults with both of my TDL ZPU boards.  

Finally, with KILLABIT running, I flipped the 2MHz/4MHz switch on the Cromemco ZPU over to 4MHz and it speeds up the program ... I tested going back 'n forth between 2MHz and 4MHz several times ... seems no problem at all changing the CPU speed on the fly, although in normal use I think I would tend to BOOT on the desired speed.  

.

[Walt Perko]

Hi, 

Thinking about a potential problem with the mini-Front Panel board ... I keep getting back to a basic pair of boards for testing backplanes ... continuity tests, test for shorts, test and display power and perhaps a few other tests if possible, but then maybe some rudimentary tests with a front panel, CPU board and RAM board?  

.