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Thread: IT pro turned amateur

  1. #1
    Join Date
    Aug 2020
    Location
    Winchester, UK
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    18

    Default IT pro turned amateur

    My dad brought home an Exidy Sorceror in 1978 or 79, when I was 15 years old. I learned to program on that machine, later moving to BBC Micro. It was my number one hobby, but I never had a thought of making it a career until I was almost through university. Finally it dawned on me I could make a living doing what I loved. In a 35 year career I was a software developer, network specialist, technical and enterprise architect, consultant, lecturer. I had plenty of fun, but as I moved up the ladder had fewer and fewer opportunities to just play with computers, and I missed it.

    I'm now fully retired, and seem to have returned to that early enthusiasm. Lately I've been learning something about electronics - which is new to me. Following I guess a typical hobbyist path of Arduino, microcontrollers, small circuit design. I still have that Sorceror. I tried firing it up a while ago and it hummed but didn't display anything. I have an ambition to see it working again. It's quite daunting and I'd love to have access to a community who might be able to help me with that task.

    I'm in the UK.
    Rob

  2. #2
    Join Date
    Jun 2016
    Location
    Guisborough, England
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    Default

    Hello,

    Lacking a response from someone familiar with this machine, I'd suggest that it might help your cause to supply some extra information.

    Firstly, it's not clear from your comments as to if it's the actual computer that's not working, or the monitor unit that should be attached (and is the connection between the two verified).

    Secondly, I understand that there are different options for the ES, and you don't say how yours should start up, from ROM, or from cartridge, or if you've got a floppy drive for CP/M use?

    Geoff
    Vintage Devices: Epson HX-20/TF-20, Amstrad PCW 8256 (with extras), 386 and 486 PCs with 5.25 and 3.5 floppy drives, Pentium 75 with Roland LAPC-I midi card

  3. #3

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    We can walk you though trouble shooting the hardware.
    We'd need information on what test equipment you have?
    We don't know which machine you have. You can find some documentation at http://www.bitsavers.org/pdf/exidy/ .
    It would be useful to know which hardware you have?
    Dwight

  4. #4
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    Aug 2020
    Location
    Winchester, UK
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    Default

    Hi Geoff, Dwight,

    Thanks for the replies. I only meant this post as a personal intro as I'd just joined the site. I'm not yet quite geared up to start the debug and will start a new thread in a more appropriate area when I'm set to go.

    The machine is the first edition Sorceror, with 32K and Basic ROMpac. Cassette interface only, no discs. As I mentioned, we had the S-100 chassis but it hasn't survived. I currently only have a multimeter and a cheap logic analyser, but I'm planning to get an oscilloscope for this and to progress my other learning projects. The simple, quick test I did a while ago was just to plug the composite output into the AV port of a monitor and power on... there was no display. No smoke, no obvious overheating. So I know there are a wide range of problems that might account for that. Dwight, thanks for the link to that document store, that looks really useful. I'm gathering together relevant info before I embark on this.

    Will pop up again in another forum in due course.
    Rob

  5. #5
    Join Date
    Jun 2012
    Location
    UK - Worcester
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    Default

    First of all Rob (as this is your first post) welcome to VCFED.

    Yep, let us know what machine you have and what test equipment you have access to. A decent multimeter is a must. I have both an analogue and a digital one. They are generally used for different things. An oscilloscope is also useful. If you haven’t got one of these, they can be acquired these days quite cheaply. The cheapest ones are limiting for the frequencies we are talking about on a Z80 ES.

    Can you understand electronic schematics would also be a bit of useful information.

    Also, how are your soldering/desoldering skills if you have to replace some components? Perhaps get a bit of practice in with some cheap components from eBay!

    Just note that you will be moderated for the first few posts. This is designed to keep spam off the board, and it works very well. Just be patient...

    Dave

  6. #6

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    Quote Originally Posted by robjordan View Post
    Hi Geoff, Dwight,

    Thanks for the replies. I only meant this post as a personal intro as I'd just joined the site. I'm not yet quite geared up to start the debug and will start a new thread in a more appropriate area when I'm set to go.

    The machine is the first edition Sorceror, with 32K and Basic ROMpac. Cassette interface only, no discs. As I mentioned, we had the S-100 chassis but it hasn't survived. I currently only have a multimeter and a cheap logic analyser, but I'm planning to get an oscilloscope for this and to progress my other learning projects. The simple, quick test I did a while ago was just to plug the composite output into the AV port of a monitor and power on... there was no display. No smoke, no obvious overheating. So I know there are a wide range of problems that might account for that. Dwight, thanks for the link to that document store, that looks really useful. I'm gathering together relevant info before I embark on this.

    Will pop up again in another forum in due course.
    Rob
    Get at least a 50MHz sample rate scope if digital. There are lots of good used 100MHz analog scopes available. Do look for one with delayed sweep.
    Dwight

  7. #7
    Join Date
    Jun 2012
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    UK - Worcester
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    Rob,

    I assume you have looked at the treasure trove of documents that Dwight pointed you at (http://www.bitsavers.org/pdf/exidy/)?

    As you have already powered it up and tested to see if it lets the black smoke out - and it doesn't...

    The first thing to do is to identify exactly what you have got - and identify the correct schematics for the beast. Either look for part numbers on the board and do it yourself (and point us at what you have found) or post some high-res photographs somewhere that we can get to for us to look at.

    The fault finding procedure for most computers is generally exactly the same. There is no 'magic' formula!

    Check the power supplies, then look for the presence (or absence) of clocks, then look for some of the control signals to the microprocessor (a Z80 in your case) not being correct. For example, is the Z80 being held in a permanent reset? Is something generating a permanent interrupt that is confusing the Z80 microprocessor etc.

    The power supply checks can (initially) be done with a cheap and cheerful multimeter. It will not tell us everything (i.e. it wont tell us if there is too much ripple or noise coming from the voltage regulators) but it will tell us if one of the dc regulators is completely dead or not generating the correct voltage...

    What logic analyser have you got? That could turn out to be a useful piece of test equipment!

    We're here to help you. Don't be too daunted - many people have got their old treasured machines working with virtually zero knowledge to start with and minimal test equipment - so you are not alone in this venture! I am quite certain we can provide the help you need. However, we just need to do things methodically...

    Dave

  8. #8
    Join Date
    Aug 2020
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    A quick update from me about the Sorcerer. Thanks for all your contributions! The excellent news is that the machine is basically working! One small issue I'm aware of (described later) but it's not a show-stopper.

    I put up an album of photos here. Some have text descriptions explaining the content.

    I haven't consciously done anything to repair it... I opened it up, gave it a very light clean, removed and reseated circuit boards, checked supply voltages, which are +4.8, -5.2, +11.5; apparently close enough to +/-5 and +12. Oh I also removed the giant 8000uF capacitor and tested it for leakage and it seemed fine (30uA leakage after 5 minutes, dropping to 20uA shortly after). Maybe these interventions helped in some way, but I suspect my prior test a couple of years ago was flawed. That time I just plugged the composite output into a TV, and saw no output. This time I connected it via a handy SCART-to-HDMI converter to a PC monitor, and right away it booted to the Exidy Monitor.

    The only defect I'm aware of is that the BASIC ROM Pac isn't working (screen fills with alternating 0/9 pattern). I suspect I'll need to replace one or more of the PROMs with a new EPROM. Terry Stewart has comprehensively documented the process he went through to repair a failed ROM Pac.

    I've also downloaded Tezza's amazing software trove and I'm exploring it. Loading via the tape interface is very troublesome, especially at 1200 baud, but I have succeeded occasionally. The oscilloscope I bought to help with the expected fault-finding has been handy for tuning audio levels and I'm sure it will be well-used in future. The experience has given me the ambition to implement some way of loading software over an electrical, rather than audio, interface, i.e. serial or parallel. I saw someone had connected a Teensy microcontroller with SD card directly to the Sorcerer UART. It's a great idea and one I'd like to follow up on. With that in mind I wrote a Python script that can demodulate the tones from WAV files and save the program in a binary format.

    Thanks for all the documents you have alerted me to. It does seem the Sorcerer was, and is, an exceptionally well-documented, and well-engineered system. Another document that I found very useful and quite readable (maybe familiar to some of you): Steve Ciarcia's 'Build Your Own Z80 Computer'. The whole content is on Google Books.

    Having fun! Thanks.
    Rob

  9. #9
    Join Date
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    Repairing faults like that are the best!

    Over on the NASCOM google group Neil has developed a solid state replacement for the cassette player to load software. Sounds like a similar thing as you mention...

    I am also working on a PIO connected SD-CARD interface for the NASCOM using an SD-CARD breakout board with a 5V to 3.3 Volt regulator and voltage converters built-in.

    Fortunately, we have the sources for PolyDOS available so we can modify and reassemble the disk drive interface software to suite our own requirements. I am sure there would be a similar way to add a unit on to the Exidy, but you will have to explore that avenue yourself.

    If you can get a few more posts under your belt (>10) then your posts should stop being moderated.

    I look forward to further progress on your Exidy...

    Dave

  10. #10

    Default

    Welcome Rob, and thanks for sharing your findings. Tezza’s software library is one of a kind. One thing to note is that the 1200 baud versions are really suitable only for the MAME Sorcerer emulator. Actually I am surprised to hear you managed to load one of them. On a real Sorcerer you can use the 300 baud versions. They should load reliably.

    The monitor defaults to 1200 baud. To set it to 300 baud you need to enter
    SE T=1
    in the monitor.
    Of course you can then switch back to 1200 baud (SE T=0) and save the program for future re-loads.

    The Exidy Sorcerer is quite uncommon and as a result has a modest active community.

    The BBC Micro however has a very active community also still developing new hardware and software projects. Have a look at the Stardot forum for more info.

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