AES (Lanier) 103 (aka Beaugrand Alphatext)

    3x 7406 bad (floppy drive drivers, ooen collector Schmitt NOT)

    1x 74121 monoflop bad

    1x NE558 monovibrator bad

    1x 74374 flip-flop bad


    I think the power supply failure took out a bunch of TTL. Adding to the list as we go.

    Zitat von mister-freeze

    I admire your persistence. I think most people would have given up on the project long ago.

    Hope your effort will soon be rewarded with a working AES.

    With your discs, that made the prospect of this machine working again viable!


    I enjoy the challenge. It's helping me understand the computer better, which is something I like. Years ago I took a class which involved troubleshooting at this level and writing Z80 assembler, but my understanding of the processor and the rest of the system attached to it was limited as it was a rapid class.


    This has given me that opportunity again to try determine what's wrong, and in doing so, expand my knowledge.


    Phil

    There's a later model AES i/o board on eBay- well, was. It's just been purchased.


    It should serve as source of spare 74xx logic and most importantly the SMC COM2601.


    I looked and that chip has Vcc and Vdd power- it will have been run without Vcc which won't have done it any good at all.


    I'm working on the logic layout right now for all the different floppy drive functions.


    Phil


    Top drive, drive-enable (2).

    Quite simple, bus bit 1 driven high, encoder chip 44 (74138) given 3 bit code, drives CLOCK one state over on chip 17, copies bus bits to output, drive latches on.


    Need to draw the rest of the board but this bit is enough for tonight.


    Phil

    I started putting the index signal lines in but that got too complicated too quickly so I started over.


    Drive read data path. Working on the multiplex selector path now.



    Little wonder if wasn't working at all; the 74121 is integral to the bitstream, between it, the NAND gates and the flip-flop it forms a crude shift register to feed the UART serial data in.


    Phil

    Recieved some 20-pin chip sockets in the mail so continued testing buffers last night. Got 6 done, another 5 on this board to go.


    However right now, I'm having a break to let some acetaminophen kick in because I've got a headache that's not good for concentration. (My advice to avoid this: If you were planning on having children, don't).


    Phil

    Board with spare COM 2601 chip arrived today.



    Now i need to order some of the other TTL chips that are bad

    The COM 2601 has +5 and -12V supplies, and doesn't do much when tested. Hence purchase of this board. Hopefully this one isn't bad. I'm guessing it doesn't like the +5V rail to be gone for an extended period.

    Still the cheapest COM 2601 on eBay, to buy the whole board, and it does provide some spare chips.

    It's a year newer (1979), and AES have taken to socketing most of the chips. I guess they learned that lesson...


    Phil

    Floppy drive data path (read, write) multiplexors (74157).

    Both have trouble and start to go glitchy after about 300kHz.

    Pulled one off the spares board that came in today. First time it's seen power probably in decades and there it is running faultlessly at 3.5MHz.


    Anything connected to or in the path of the floppy disc drives appears to be bad.


    Phil

    I took a look at connector J5. It is not populated with a pin header, nor does it have the chips required to operate it.



    However, doing a little looking at the circuitry, my best guess is that chip 18 would be a 74LS273N and chip 10 a 74365AN.


    Reasoning for that is the connections to the bus and chip enable lines make sense, and for a line driver to be the final stage also.


    I would need to look at the connections in more detail but I think this is an unused header for LED's- drive enable, operation etc.

    The operation of these lights has been taken directly off the front panel backplane now, so that makes it redundant.


    Phil

    That's all the bad chips on the I/O board replaced.

    Result?


    No


    Edit: Slight change noticed: pulling the CPU card and powering up now causes a nice steady beep from the speaker, which is generated on the I/O board. It didn't do that before.


    CPU card next!

    Einmal editiert, zuletzt von PhilA ()

    Gefällt mir 1

    This project is on hold for a while.


    Unfortunately I got pretty hard hit by hurricane Ida at my house; water leaked in where the roof was damaged. My garage collapsed because of a tornado.

    We are still in Texas. I cannot do much to the house until the electricity is put back on.

    Zitat von PhilA

    This project is on hold for a while.


    Unfortunately I got pretty hard hit by hurricane Ida at my house; water leaked in where the roof was damaged. My garage collapsed because of a tornado.

    We are still in Texas. I cannot do much to the house until the electricity is put back on.

    Too bad! Good luck with repairing the house/garage, clearly this is more important than fixing old computers...

    Electricity service is restored to the house.

    Went yesterday and the roof was continuing to leak so I added more plastic sheeting to the roof.

    At least now the air conditioner is running and acts as a dehumidifier, so that'll help somewhat.


    House isn't good to live in yet, very damp and moldy.


    Phil

    Still away from home. A little searching is going on for my Multitech MPF-1 Z80 prototyping board, because I would like to write a little assembler and create a rom or rom emulator that'll at least test if the 8080 is initializing (nop loop, for instance).


    I'm thinking an Arduino might have enough grunt to act as a ROM?

    I removed the UART because it was holding some of the data lines low- its only task is to serialize the parallel data from the keyboard, which in this machine is not used.

    That led to the keyboard responding a little bit- it will repeat the last key pressed indefinitely, and some keys are not working. Looks like the keyboard decoder has 2 bad matrix lines unless I have shorted switches.

    I shall desolder the decoder and test, but before then I need to see if the "a key is pressed" output is being held high, and the data repeated.


    Phil

    I pulled one of the keyboard chips out and bypassed it, driving the "data ready" pin direct from the "key pressed" output of the keyboard decoder.


    The computer registered a key press on all but the number 7, return, backspace and space. All it did was produce the digit 7 on the screen unless SHIFT was held and it produced the digit / and if CTRL was held it produced ÷

    I don't have the datasheet for the keyboard decoders, and the keyboard is particularly strange in terms of layout. I think that is so it can detect dual key presses.


    I had a thought tonight, I think I'll rig up a counter and push 00 to FF down the keyboard bus and see what the board makes of it.


    Phil


    Disconnected keys until the keyboard started to work.

    Space, return and backspace disconnected and it allows me to type.

    That's narrowed down to 3 keys, common is the lower pin which makes the keyboard upset; too late today to carry on but that's progress.


    Phil

    PhilA , that's great, glad you made it.

    In the meantime I found a manual in english language. If you want I can scan it sometime. It is however so that the control commands (letters for function selection) in the English variant is different to the German. Since you have the German operating system, this probably won't help you at first. How does it behave with the keyboard layout ? Some keys might be assigned incorrectly due to the different keyboard layouts.

    Hopefully you will get the US version of the operating system someday.