I think it's the mini-Front Panel ...

[Walt Perko]

Hi, 

Yesterday, in the ZOOM https://www.youtube.com/watch?v=I8KbNbLPmNw

It seems odd that moving the boards around on the backplane to find a setup that functions as it should.  

I did some more testing after cleaning the bottom edge connectors of the TDL ZPU board (oldest board) and even the mini-Front Panel board (only a few months old) ... 

Then I tested with another ZPU board and then with a different backplane ... it's always the same shifting problems ... 

This has me convinced the problem is in the mini-Front Panel board as the other boards all work perfectly in other computers.  

The next problem is to determine, does the board need a chip or other component replaced to make it stable?  

I wonder if anybody can spot an incorrect component on the mini-Front panel?  

.

[Walt Perko]

Hi, 

The thing is the TDL ZPU worked in the IMSAI-JAIR computer (my first mini-Front Panel) computer.  The FlexRAM worked in another computer no problem.  

Now that I've swapped out the backplane and still get the same floating errors, it seems the mini-Front Panel has to be somewhat flakey.  

The switches for the third mini-Front Panel board are inside the USA, cleared customs ... they could arrive any day now and then I'll have that mini-Front Panel board built for testing too.  

What I hate is the BOM for the mini-Front Panel boards seems to be for an older version of the board ... a couple of the capacitors are suspect ... especially C3 and C4 ...

.

[Joseph Corda]

Walt.. 

Yeah I have the same question about the MiniFP BOM as I have a REV F Mini FO board and the BOM on S100 does not match ..

So far I built mine board using a BOM from REV E and a BOM from a full size CP-A board when I had question about a part missing from Rev E BOM

Crossing my fingers that it will work once I get the rest of the parts received and  installed .. only have just some switches and insertion the IC's left to do

Joe

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[Patrick Linstruth]

Walt, when the system wasn’t working, SINP looked like it wasn’t making it from the CPU card to the bus since both the FP and 2SIO appeared to not see the signal. That may point the finger at the TDL ZPU card. Since the problem appears to be intermittent, it may not be relevant that it worked in a different system before. It could be a problem with ICs 10, 11, or 13.

It is also SINP that had an open connection on slot 2 when the backplane was at my place. It’s possible the problem wasn’t the solder joint and the connector is is bad. I don’t remember what you had plugged into slot 2 during the Zoom call.

On Nov 3, 2025, at 2:25 PM, Joseph Corda <jjco...@gmail.com> wrote:

Walt.. 

Yeah I have the same question about the MiniFP BOM as I have a REV F Mini FO board and the BOM on S100 does not match ..

So far I built mine board using a BOM from REV E and a BOM from a full size CP-A board when I had question about a part missing from Rev E BOM

Crossing my fingers that it will work once I get the rest of the parts received and  installed .. only have just some switches and insertion the IC's left to do

Joe

On Mon, Nov 3, 2025 at 2:03 PM Walt Perko <r4r...@gmail.com> wrote:

Hi, 

The thing is the TDL ZPU worked in the IMSAI-JAIR computer (my first mini-Front Panel) computer.  The FlexRAM worked in another computer no problem.  

Now that I've swapped out the backplane and still get the same floating errors, it seems the mini-Front Panel has to be somewhat flakey.  

The switches for the third mini-Front Panel board are inside the USA, cleared customs ... they could arrive any day now and then I'll have that mini-Front Panel board built for testing too.  

What I hate is the BOM for the mini-Front Panel boards seems to be for an older version of the board ... a couple of the capacitors are suspect ... especially C3 and C4 ...

<IMG_928820251103-mini-Front Panel #2-c2K-Capacitors.JPG>

.

On Monday, November 3, 2025 at 9:13:35 AM UTC-8 Walt Perko wrote:

Hi, 

Yesterday, in the ZOOM https://www.youtube.com/watch?v=I8KbNbLPmNw

It seems odd that moving the boards around on the backplane to find a setup that functions as it should.  

I did some more testing after cleaning the bottom edge connectors of the TDL ZPU board (oldest board) and even the mini-Front Panel board (only a few months old) ... 

Then I tested with another ZPU board and then with a different backplane ... it's always the same shifting problems ... 

This has me convinced the problem is in the mini-Front Panel board as the other boards all work perfectly in other computers.  

The next problem is to determine, does the board need a chip or other component replaced to make it stable?  

I wonder if anybody can spot an incorrect component on the mini-Front panel?  

.

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[Walt Perko]

Hi, 

The thing is when I swap out the TDL ZPU for a Cromemco ZPU which I also know is working just fine in the IMSAI-JAIR computer I still have the exact same symptoms!  Same with swapping out the FlexRAM with another FlexRAM board, and swapping out the backplane.  

The only consistent board is the min-Front Panel board.  

.

[Patrick Linstruth]

The only consistent board is the min-Front Panel board.  

And the backplane.

To cause what we were seeing, it seems either the CPU board wasn’t able to assert SINP on the bus, the connector is bad, or something else is pulling it to ground. Since it’s an input on the FP, I am not sure how likely that is.

Are you still able to reproduce the problem, or has it gone away?

If you can reproduce it, very easy to test.

Enter DB 10 (IN 10H) on the front panel and single step. When 1010H appears on the address bus, if the INP light isn’t lit on the FP, probe the bus and see if SINP (46) is high. If not, probe IC 10 pins 9 and 10 on the TDL ZPU. They should both be high during an IN operation.

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[Walt Perko]

Hi, 

The first thing I did after the ZOOM was to use some CRC QD Contact Cleaner on a rag to rub on all the bottom fingers of the boards.  That didn't change anything.  

I tried reseating all the boards multiple times in different slots ... and it's the same problems ... 

So the next step was to swap out the backplane ... again, it's all the same floating around problems ...  

Then I swapped out the TDL ZPU for a Cromemco ZPU board ... still the same problems.  A

After that I swapped out the FlexRAM for another FlexRAM board ... still the same problems.  

I then went back to the 9-Slot backplane you worked on ... still the same problems.  

The only board not swapped out is the mini-Front Panel.  

.

[Patrick Linstruth]

Is “the same problems” the IN front panel LED not being lit during an IN instruction or are there other problems?

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[Walt Perko]

Hi, 

Today I installed the SSM CB2 Z80 CPU board ... did some testing with both the FlexRAM and then the FDC+ ... 

I noticed that things seem okay when I do a STOP - RESET ... and I can DEPOSIT and EXAMINE RAM, I ran the 2-Byte ZERORAM program (063 307) and the program ran just fine.  

When I went to dropping the ADDRESS back to 00000000 00000000 that's when the computer "Went Off Beam/Faulted."  

I did this a few times ... so there is something with the slight jiggle of the board in the slot, but maybe more likely, something with the bits on the address switches ???  

When I install the ZERO RAM program and ONLY RESET - RUN it works.  When I ONLY RESET and EXAMINE it works, but as soon as I flip any of the address switches while the computer is STOPPED ... it lights up all the DATA LEDs

.

[Patrick Linstruth]

I would need to look at the schematic for the front panel, but it sounds like the front panel may be setting /SSW_DSBL when it shouldn’t.

Just flipping one of the address switches shouldn’t have any effect on anything unless EXAMINE or DEPOSIT are pressed. A video might help.

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