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Best way to start debugging a non-working Decmate II?

tradde

tradde

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A good friend gave me a Decmate II some time back. I have never gotten it to work. Swapped in a known good floppy drive. Nothing. I know the HD is faulty.
It either does not spin up at all or spins up then back down. Disconnected it thinking maybe it would force it to go to the floppy. Nope. Have removed all boards
for inspection but nothing obvious. How does one do any board debug with the way it's designed to have the mainboard hidden? The power supply cable is
much too short to allow pulling the mainboard out and attaching it to the removed board. I'd like to see this work as I have never used one. It even has the
CP/M expansion board. Thanks for any suggestions. I do have an older scope and logic analyzer if I had some way to use them with this.
Tim R
 
I had not thought about debugging one of these. You might be able to remove the main board and the power supply from the cabinet and then cable them together to allow you access to the IC's. Knowing how it boots up will help you out. In a nutshell, It copies the ROM to the RAM in the control panel memory, jumps into the RAM image and then disables the rom. They did this because you can't use the JMS instruction in ROM. Then goes through some self tests. Charles Lasner did a reverse assembly of the ROM. Do you ever see anything on the display? If I remember correctly if the display is warmed up enough you can see it testing the display memory during the self test. if it is trying to read the floppy you see a character graphic of a floppy disk several inches across. It does some sort of flip when it is retrying. Difficult to describe what it looks like.

There is a way to feed it programs through the com port I think for factory testing. I don't know if any of that still exists or if it was even used. You can see this in Lasner's code. It would not be out of the question to write a little code and burn your own EPROMs. They are 2716 Eproms, nothing special or exotic.

Like all of these things, simplify first by removing the APU (CPM board) and the hard disk controller. You didn't mention the graphics card but remove that too if you have one. I think it used a color monitor. None of those is needed for it to work and if there is a problem with one of them they could mess up something you do need. Check the power supply first, then the clocks, then look at the ROMs to see if it looks like it is reading them when it first wakes up. A single floppy drive is cabled to the connector nearest the front of the machine. It is possible to bend pins in the floppy connectors so inspect that to make sure they are all straight. I managed to slightly bend some of mine when I unplugged the cable. Fortunately I didn't try to force it when I put it back together.

There were 3 different APU boards. One had a Z-80 with 64k of memory. One had both a Z-80 and an 8086 with 256k and the third was the same as the second with 512k of memory I think. I've never seen any of the three APU boards. I have a hard disk in mine but it doesn't boot from the HD even though it spins up. I think it is supposed to read the first sector and then looks at the first few bytes. If it doesn't match what it expects it boots from the floppy.

I hope you choose to work on this. If so please post about your adventures.
 
"I think it used a color monitor." - Yes, the VR201 was available in white -A, green -B or amber -C phosphor (but not a color monitor as we know it today).

"There is a way to feed it programs through the com port I think for factory testing... You can see this in Lasner's code."

IF THE PRINTER PORT HAS THE APTEN LINE GROUNDED, WE GO IMMEDIATELY INTO THE AUTOMATIC PRODUCT TEST DOWNLOAD MODE.

DIRECT DOWN-LOAD ROUTINE. CALLED VIA JMS I .+1;DOWNLOAD IF APTEN IS SET. THE FORMAT IS STANDARD PAPER-TAPE RIM FORMAT WITHOUT A LEADER. LOADING IS TO MAIN MEMORY FIELD 7. THE ROUTINE IS ALSO CALLABLE AFTER A PREVIOUSLY LOADED PROGRAM EXITS VIA A PANEL REQUEST INSTEAD OF A HLT INSTRUCTION. THIS CAUSES A TOTAL RESTART OF ALL CODE INITIALLY MOVED FROM THE ROM TO CP FIELD 7. IN THIS SITUATION, CODE LOADED INTO MAIN MEMORY 76000-77777 WILL BE MOVED TO CP 76000-7777 TO BECOME THE NEXT CP-INTERRUPT HANDLER, ETC. EXIT VIA HLT INSTRUCTION RETURNS TO A DESIGNATED ENTRY POINT TO LOAD MORE CODE.
Click to expand...

I think you'll find your scope and logic analyser will come in handy. Do you have DECmate II engineering drawings / schematics?
 
@tradde: you listed a bunch of things you tried getting it to work. But you did not tell what the actual fault is!? Does it turn on at least? (I guess it does since you mentioned the hdd spinning up)
 
There was also a graphics option available. This is the best writeup I was able to find find in the Charles Lasner ibiblio stuff.

"An obscure option for the DECmate II is the graphics board. This allows DMA bitmap and other graphics functions to be displayed on either the mandatory VR-201 monochrome monitor, or on the optional VR-241 color monitor, or both. (There are no official color-only DECmate II configurations, although there are rumored cable variations that allow a color-only configuration that is not fully supported by all software. The lack of support could merely be that the color of text could be somewhat at random under some circumstances, but it doesn't appear likely that there could be any other consequence. The only exception is that some software enabled a screen-saver option of the hardware, and it's not clear how this would be affected in such a situation, etc.)

The graphics board is capable of outputting the so-called 16 colors as usually defined on IBM-PC color adaptors, meaning 7 colors in two brightnesses, white, and black. On the DECmate III series, the output is only capable of being to up to four colors taken from a palette of 64. There is little software for the graphics board, and apparently none take much advantage of these differences."

I did find mention of 800x240 resolution which Charles did not mention.
 
I haven't messed with it for quite some time, but as far as I remember the VR201shows nothing on trying to boot. I think the floppy light blinks once but never
hear it trying to read anything from the floppy. Just after I posted this I realized I should test the power supply voltage as someone else suggested. I had also
thought that popping the PS off its base might allow me to connect it to the mainboard out of the unit. Have not tried any of that yet. PS check will be my
first thing to do. I have the field maintenance print set. The unit has the APU board and HD as expansion units. I had removed both and still the system
did nothing. Maybe it will be a simple fix with the PS not supply the correct voltages. Now I just have to find the pin-out of the plug.
 
That's better than nothing. Thanks. I did a quick voltage checking using my Radio Shack meter from decades ago. Has always been fairly accurate.
+5v seems to swing from 4.75 to maybe 5.11 volts. +12 volts is also oscillating from just under to just over. This is with nothing connected, main board
removed. Does this PS need a load on it to test?
 
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