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Thread: Powertran Cortex

  1. #151

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    Quote Originally Posted by Stuart View Post
    I'm up in Southampton. You got a new Maplins in Barnstable last year was it?
    Stuart.
    However they don't actually sell anything useful these days!

    1) if you need your 2564 programming I should have a fast turnaround this time.
    2) I have a small pot of MCM6665s which as far as I can tell are 4164 compatible. I can test 8 and put them in some antistat foam in the post.
    "Don't it always seem to go
    That you don't know what you’ve got ‘til it’s gone" (BANG )

  2. #152
    Join Date
    Jul 2009
    Location
    Southampton, UK
    Posts
    169

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    Makes sense to try a new set of 4164s if they are handy.

    Andy, when you tried your Basic EPROMs, did any of the LEDs change state once the buzzer started? Looking at the Cortex Basic ROM code, the first thing it does at power-on is copy the EPROM to RAM and it creates a checksum of the EPROMs as it goes. If the checksum fails, it switches on the buzzer and locks the system (so shouldn't get any LEDs changing state after this point - if this is what your system is doing).

  3. #153

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    Nige / Stuart, Thanks for the response and sorry for the stupid question about the DRAMs, you can probably tell this isn't my area of expertise!

    I've just tried both of my 74LS245s in position # 44 and I get the same results as before.

    I've been looking through the original build instructions and realise that in my haste to build the computer all those years ago, I don't appear to have soldered the "through holes" that make the connections between the 2 sides of the PCB. So the dilemma I have now is do I assume that the PCB, that I have had working in the past, is good and I have a component fault OR do I solder all the holes and risk possibly introducing a seperate fault between the tracks on the PCB when soldering. Any thoughts?

    Nige - If I could borrow a set of your MCM6665s for fault finding, that would be great - Thanks very much.
    Stuart - I've just checked the forum again and have seen your question about the LEDs. Unfortunately I've just dismantled everything again and placed it out of harms way, so I can't say for certain if the LEDs stop when the buzzer sounds - From memory, the symptoms change each time I press the reset button / apply power. Sometimes I get no buzzing and just the MEM and RUN lights lit. Other times the speaker crackles, the RUN light goes dim and flickers and the MEM led lights. And on some occasions I see the IDLE or BASIC led lit on their own - It just seems a bit unstable. The buzzer was definately constant after every reset before I resolved the LOW VOLTs issue. I'll give you a more accurate report when I check it again over the weekend
    Your idea of using a modified single EPROM sounds interesting and I actually have 2 of my original 2564s spare (and I assume serviceable) but I would not know how to set one up.
    Once again thanks to you both for assisting me with this, I certainly need the help!

  4. #154

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    Stuart,
    I almost replied to your question using my fig forth eproms for the LED sequence test.
    This is what I saw using both sets of eproms.
    Using the Fig Forth eproms, there doesn't seem to be a set pattern. Each time I press the reset button the sequence is slightly different. The long beeps and very short beeps seem to coincide with the MEM led lighting but on several occasions the leds will continue to change after the 1st beep has been heard almost as if the system is initiating another reset itself.
    On occasions I also see a random checkerboard pattern on the screen.
    Using the Basic Eproms, the sequence is always the same - Which would tend to match what you were saying.
    With the reset button held in, the "MEM" light is lit. When the reset button is released the MEM light stays on, the RUN light comes on for approx 1 second and then I get a continuous tone plus MEM led.
    Do these symptoms confirm that the checksum is wrong and if so what do you think I should check next OR shall I remove the main board and start to solder the "front to back" connecting holes.
    One more thing, I managed to get hold of a frequency counter and have checked the 12Mhz source and the CLK on ICs 11 and 32, all seems OK.

    Thanks

    Andy

  5. #155
    Join Date
    Jul 2009
    Location
    Southampton, UK
    Posts
    169

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    You do get a continuous tone if the checksum fails with the BASIC ROMs. The MEM LED staying on is very suspicious - according to the circuit diagram and the software it should go off when the RESET button is released. Try swapping IC17 (74LS74) with another chip on the board of the same type, and also try swapping IC15 (7 4 L S 1 3 8 ) - these two chips control the MEM LED. Also worth checking the 5V supply across these two chips as well, just to make sure you've got the power supply sorted.

    Is the board fitted in a metal case, with spacers between the case and the board? Might just be worth loosening the board and checking that no screws or anything have got stuck between them in years gone past.

    Let us know how you get on.

    Stuart.
    Last edited by Stuart; February 21st, 2010 at 12:11 PM. Reason: To get rid of that bl**dy smiley that it was displaying!

  6. #156

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    sorry Andy, haven't checked the thread for a few days, a bit of a family crisis on. I'll get 8 chips in the post as soon as I can. it feels a bit rammy to me, but that's purely a guess!
    "Don't it always seem to go
    That you don't know what you’ve got ‘til it’s gone" (BANG )

  7. #157

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    Thanks Guys,
    I'll hang fire on the soldering and try what you've suggested.

  8. #158

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    Stuart,
    I've just done the IC swap for positions 15 + 17 and the fault is the same.
    (I had a spare 74LS138 and I exchanged the ICs in sockets 17 + 92)
    The voltage across the two was 4.91v.
    My circuit diagrams have different names for the LEDs but I'm assuming from the wiring to the front panel that the LEDs are as follows:

    IAQ = RUN = LED3
    MAP = BASIC = LED2
    TIME = MEM = LED4
    IDLE = IDLE =LED1

    So my diagrams seem to indicate that the MEM LED is connected to IC64.

    I've also checked under the main board and there does seem to be anything touching the tracks.

  9. #159
    Join Date
    Jul 2009
    Location
    Southampton, UK
    Posts
    169

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    Hi Andy,

    Your labelling of the LEDs doesn't seem to match the wiring given in the contruction instructions. According to the instructions:

    LED1 = IDLE on circuit diagram = IDLE on front panel (2nd LED from left)
    LED2 = MAP on circuit diagram = MEM on front panel (3rd LED from left)
    LED3 = IAQ on circuit diagram = RUN on front panel (left-most LED)
    LED4 = TIME on circuit diagram = BASIC on front panel (right-most LED)

    Do you want to check your wiring and see what is connected where? IC64 drives the TIME/BASIC LED, and that *should* be lit on and after a reset. I think the LED problem is going to be just a wiring or labelling error, which leaves the problem with the EPROMs.

    The EPROMs were blown by Nige? When you've received and tried the RAMs he's sending you, perhaps send the EPROMs back and ask if Nige can test them in his Cortex? That would rule out any problems with the EPROMs or the source files Nige used to program them.

    Is there a memory map of the Cortex available? Anyone know where the 256 bytes of memory on the processor itself is located? On boot the workspace is at >F0DC - is this in the on-chip RAM?

  10. #160

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    Only problem with my cortex is that I don't know if it's a go-er yet. I daren't just power it up, and I still haven't a space I can strip it sufficiently to test it. I suppose I could pull my roms & check them against the images I have... I'm sorry about this there's a bit going on at the mo to say the least......

    edit.... oh go on then, it's only 8:20 I'll go upstairs, finish writing the disks, put the sirius away & get the cortex out!
    "Don't it always seem to go
    That you don't know what you’ve got ‘til it’s gone" (BANG )

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