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DavidMil

Bare 850 Printed Circuit Board.

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I pulled out my 850's and set up a test machine in a corner. I knew at least one of my 850's was guaranteed to have different firmware.

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You're welcome Nezgar!

 

Okay My testing method was not precise. I've re-tested both 850's here. The both behave the same. My previous invalid tests I was doing SELECT+RESET (U1MB cold boot) and that does NOT allow reloading of the R: handler. However a proper power off then power on of the computer itself allows the R: handler to be downloaded again without power cycling of either of my 850's.

 

However both 850's do not allow multiple loading of the R: in the same powered-on session of the 800XL (so it seems), except if I power cycle the 850 then I can download the R: handler again as many times as I want without rebooting the Atari. This is fun now that I'm mid-life. :) That R: handler beep is a great nostalgia sound for me! haha

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Posted (edited)

I pulled out my 850's and set up a test machine in a corner. I knew at least one of my 850's was guaranteed to have different firmware.

 

Wow a black metal one! Awesome! If I was a woman I'd marry you.

Edited by Sugarland
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Any idea what the version level is on the ROM Chip?

 

DavidMil

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I pulled out my 850's and set up a test machine in a corner. I knew at least one of my 850's was guaranteed to have different firmware.

 

Dude! Nice early black metal case. :thumbsup: It would suggest an earlier revision ROM...

 

Can you post the 9201359A ROM file here?

 

Could you also post a picture of the chip in that box?

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Dude! Nice early black metal case. :thumbsup: It would suggest an earlier revision ROM...

 

Can you post the 9201359A ROM file here?

 

Could you also post a picture of the chip in that box?

 

 

Pretty unremarkable, really. Just a 2532 EPROM with a handwritten label.

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9201359A.ROM

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You're welcome Nezgar!

 

Okay My testing method was not precise. I've re-tested both 850's here. The both behave the same. My previous invalid tests I was doing SELECT+RESET (U1MB cold boot) and that does NOT allow reloading of the R: handler. However a proper power off then power on of the computer itself allows the R: handler to be downloaded again without power cycling of either of my 850's.

 

However both 850's do not allow multiple loading of the R: in the same powered-on session of the 800XL (so it seems), except if I power cycle the 850 then I can download the R: handler again as many times as I want without rebooting the Atari. This is fun now that I'm mid-life. :) That R: handler beep is a great nostalgia sound for me! haha

 

 

Not really an issue anymore. I wrote a reset program, just run it to cold start the 850 with out powering anything off: http://atariage.com/forums/topic/289938-bare-850-printed-circuit-board/?p=4267216

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A 2532 EPROM? Further suggesting 'early release'.

But that gets me thinking.. I have some 2532s, I didn't think of trying one in my 850 because I got one working in a 1050 in the 2332 mask ROM jumper configuration, but it required inversion of the CS/PD (A14/Pin 20) signal to get it to work, otherwise it gets a permanent 'low' causing it to never disable and clobbers (repeats itself) in the lower 4K in the memory map. Will be interesting to compare what that 850 board does compared to one shipped with a mask ROM. I'll have to try it.

It's possible the behaviour of that early 850 was modified to put an inverted signal on pin 20. I recall the assembly instructions for the bare board had optional steps for using a 2732, which implies an inverted A14/CS/PD signal is available somewhere on the board.

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The 850 should be able to load it's handler devoid of DOS

The 850 should be able to send the handler without power cycle of the 850 for ROM/CARTRIDGE/CASSETTE/BUS CARD configurations.

The 850 should be able to keep the R1: - R4: devices connected with the control lines asserted in the last state they were in before a reset of the Atari itself.

The 850 should be able to send the Handler to the Atari any time the Atari requests it using whatever method the Atari happens to use with the following condition.

The 850 handler should be removed from HATABS / Un-linked and Removed from memory before reloading the handler.

The 850 should be accept reset command by the Atari and drop all connected devices, and then appear to the Atari as initial power on has just occurred.

The 850 must accept code/data sent for modify/test and control operations.

The 850 must operate at 9600 Baud without losing characters.

if any of those conditions fail the 850 is not suitable for network connection and should be exchanged for one that does.

 

does any 850 in wild meet those conditions?

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A 2532 EPROM? Further suggesting 'early release'.

 

But that gets me thinking.. I have some 2532s, I didn't think of trying one in my 850 because I got one working in a 1050 in the 2332 mask ROM jumper configuration, but it required inversion of the CS/PD (A14/Pin 20) signal to get it to work, otherwise it gets a permanent 'low' causing it to never disable and clobbers (repeats itself) in the lower 4K in the memory map. Will be interesting to compare what that 850 board does compared to one shipped with a mask ROM. I'll have to try it.

 

It's possible the behaviour of that early 850 was modified to put an inverted signal on pin 20. I recall the assembly instructions for the bare board had optional steps for using a 2732, which implies an inverted A14/CS/PD signal is available somewhere on the board.

 

 

There are two traces cut (one on top and one on bottom) and a transistor is used as an inverter.

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The trace layout looked like is was almost set up to allow that to be a jumper/bridge option at one time :)

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There are two traces cut (one on top and one on bottom) and a transistor is used as an inverter.

 

All makes sense now, thanks for the pics! So the base PCB is probably no different to the later units. Pin 20 inverted via the transistor as you said, and pin 21 grounded (otherwise for programming at +21 or +25V). I will wait until my 2332 adapters arrive. :D

 

EPROM has date code "8023" = June 1980

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That's so cool, very much appreciated! I remember reading previous threads about the test mode and thinking something like this might be possible.

 

Maybe printing some kind of checksum or hash (ZIP compatible CRC32?) on screen as part of the program might be helpful to help people running it determine if they have a ROM with a known dump, or something new, without having to then transfer the file to the PC or have others on AA to check the file?

 

I ask because I'm tempted to start a new thread with a title specifically as a campaign for all 850 owners to run it to check if we can find the additional versions suspected to exist. (at least 2)

 

I'm also in favor of starting a new, "Calling all 850's" type thread. I ran the program on all three of my 850's and all of them are 2CF990B9.

Attached is a pic of one of my 850 result screens. One comment about warerat's wonderful program; If you have more than one 850 you'll

want to rename the file after each save or it will overwrite the results of each previous save with the info of subsequent saves. Other than

that; this is a really great utility! Hats off to warerat!

 

DavidMil

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Then sadly, in my haste I fell for the ol chip orientation trick, as I did not take note of the orientation prior to extraction, and it was not immediately apparent to me which way the socket was keyed.. The bloody 6507 is reverse orientation of the ROM too.. Anyhow, i got it backwards, and probably blew the ROM when I went to test it... blarg

 

Quoting one of my earlier posts in this topic. :) DavidMil kindly sent me a spare original ROM to try in my 850, but it also didn't work. Then I re-dumped both chips using a socketed Atari 8K cartridge PCB (showing at $B000-BFFF) and was happy to confirm that BOTH ROMs are actually still good, and verify CRC32 2CF990B9.

 

I then replaced the ROM socket on the 850 PCB with a new machine socket not trusting the original that I had also partially damaged, also to no avail with either ROM. (absolutely no audible difference to the boot sound with the 850 attached or not with no disk drive attached)

 

Swapped the 6507 into a 1050, and it works there, so the CPU is OK.

 

I reseated every other chip on the board, and even reversed the two identical RIOTs between the two sockets. (I guess I could test them individually in a 1050 as well...)

 

A quick DMM Ohms check on each capacitor in-circuit showed expected slow gain to 0 ohms indicating it is taking up some charge, not seeing and obvious direct shorts or lack of continuity.

 

Full disclaimer: I'm pretty sure this 850 didn't work before I started all this now , but I'm interested to figure it out if anyone has any ideas...

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Posted (edited)

 

Quoting one of my earlier posts in this topic. :) DavidMil kindly sent me a spare original ROM to try in my 850, but it also didn't work. Then I re-dumped both chips using a socketed Atari 8K cartridge PCB (showing at $B000-BFFF) and was happy to confirm that BOTH ROMs are actually still good, and verify CRC32 2CF990B9.

 

I then replaced the ROM socket on the 850 PCB with a new machine socket not trusting the original that I had also partially damaged, also to no avail with either ROM. (absolutely no audible difference to the boot sound with the 850 attached or not with no disk drive attached)

 

Swapped the 6507 into a 1050, and it works there, so the CPU is OK.

 

I reseated every other chip on the board, and even reversed the two identical RIOTs between the two sockets. (I guess I could test them individually in a 1050 as well...)

 

A quick DMM Ohms check on each capacitor in-circuit showed expected slow gain to 0 ohms indicating it is taking up some charge, not seeing and obvious direct shorts or lack of continuity.

 

Full disclaimer: I'm pretty sure this 850 didn't work before I started all this now , but I'm interested to figure it out if anyone has any ideas...

Possible bad 3086. Swap A109 with A110 or one of the other CA3086. Edited by warerat
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Possible bad 3086. Swap A109 with A110 or one of the other CA3086.

 

Thanks for the tip warerat! I swapped A109 and A110, but unfortunately no diff. Also tried swapping A107 and A108 into A109.. Booting the Atari with only the 850 and no drives attached does not load the handler, and calling it from DOS also does not respond.

 

I've also now tested both 6532/RIOT chips in a 1050, and they work just fine there. so the 4 main IC's are confirmed good. (RIOTs, CPU, ROM)

 

I have a DMM and logic probe, so thought I'd start going through the field service manual and see how far I get... Here's a summary of my findings:

 

  • Confirmed Vcc/Vpp READY coming from the computer correctly controls the reset state of the CPU. Z101 pin 10 and CPU pin 1 (reset) changes from low to high 200ms after the computer is powered on as described. (no delay when reading pin 10 on the SIO port)
  • I measure a good +5V DC, +10V DC and -8V DC at the relevant points. I don't have an oscilloscope, so can't check for ripple, but the DMM readings were steady.
  • Z102 (4013) pin 12 & 13 show a pulse, not sure the frequency. I don't think I'm able to verify If the clock is out of spec without an oscilloscope.
  • Testing the least significant address bit of the CPU on pin 5 shows a pulse, showing CPU activity.
  • Phi2 output from the CPU to the 6532's shows a pulse (pin 28 on CPU)
  • RAM is OK, no pulses seen on pins 3, 5, or 7 of the parallel port when the computer is turned on.
  • SIO command frames from the computer via 3086 A109A can be seen pulsing on pin 8 of of the A104 6532.
  • SIO ACK signals are supposed to be coming from pin 13 of the A104 6532, but I only see a steady 'high' on this pin, no matter the state of the computer.

So that last point is where' I'm stuck. I can see the 28 boot SIO command frames getting all the way to the 6532's, but nothing going back. the flow chart suggests "Replace A106 (LM349), A108 (LM349), and/or A104 (6532)" ... But I've swapped around most of those with no difference in behaviour seen. It would be odd for all to be bad, and I already know the 6532 is good.

 

Even if one of the 3086's was bad, I would think I should see A104 6532 emitting SIO ack signals at the pin of the chip.

 

Maybe clock is enough out of spec it can't decipher the SIO?

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I measure a good +5V DC, +10V DC and -8V DC at the relevant points. I don't have an oscilloscope, so can't check for ripple, but the DMM readings were steady.

If you set your DMM to AC volts when connected to the DC output it should give a reading of the AC ripple, the range will need to be adjusted since this should be low.

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If you set your DMM to AC volts when connected to the DC output it should give a reading of the AC ripple, the range will need to be adjusted since this should be low.

 

That's a neat trick, didn't know that, thanks! With that I see 0.001V ripple on +5V and +10V, 0.002V ripple on -9.25V...

 

I don't have a 2nd 850 to swap parts from, so maybe I should just order a set of 5x 3086,and 2x LM349...

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