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Thread: Where to start?

  1. #1
    Join Date
    Feb 2015
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    Default Where to start?

    Chuffed by the resuscitation of a Model 100 and a Model 102 I have just acquired a Model 4. Only two problems: It doesn't light (reportedly) and I know nothing about these machines.

    I'm hoping somebody who knows the machine more intimately can point me in the right direction. Especially what NOT to do. Kaypro this ain't.

    Thanks,

    -CH-

  2. #2

    Default

    TRS-80 model 4 has 2 common base versions a NON-GA (Part no. 25-1069) and GA (part No. 25-1069A) there are other variations (see Ira Goldklang's TRS-80 Web Site for complete details of all variations.

    basically if

    Catalog: 26-1069
    Picture Tube: Early version Black and White, later version Green, RS-232 Port Direction: Faces the bottom of the unit (i.e., down), Arrow Keys: Early version, not clustered (up/down and left/right were on 2 different sides of the motherboard), later version, clustered arrow keys, Implementation of I/O: Disk Drive Controller, Sound Card (for beeping), and RS-232 were implemented via daughterboard, Socketed: Processor was socketed (so that it could be replaced with a Z800 when/if it came out, which it never did) and Z800 Support chips were present. Memory Manager: Programmable Logic Array (PAL)

    Catalog: 26-1069A
    Picture Tube: Green, RS-232 Port Direction: The RS-232 port faces the back of the unit (i.e., out), Arrow Keys: Mostly Clustered, some versions may have non clustered arrow keys. Why clustered? Lore has it that Tandy was trying to copy Apple’s keyboard layout. Difficulty in playing games with clustered arrows, however, resulted in later models being changed back to non-clustered. Implementation of I/O: Disk Drive Controller, Sound Card (for beeping), and RS-232 were on the motherboard, Socketed: Processor was socketed, but Z800 support was dropped, Memory Manager: Gate Array

    Base models are build around the following hardware options:
    Microprocessor. 4MHz Z-80A (2 MHz in Model III mode)
    Memory: 14K ROM, 64K RAM expandable to 128K (provides for disk drive emulation in RAM).
    Keyboard: 70-key typewriter-style with datapad, plus control, caps and 3 programmable function keys (F1, F2, F3).
    Video Display: 80 x 24 (Model 4 mode), 64 x 16 (Model III mode) or double-width 40 or 32 characters per line. Upper and lower case and reverse video (Model 4 mode). 96 text. 64 graphics and 96 “special” characters.
    Language: Microsoft 5.0 BASIC
    Sound: Obtainable from BASIC. Roggled “keyclick”
    Disk Drives: One or two built-in double-density 184K 5-1/4″ drives.
    External Connections: Cassette operation at 500/1500 baud. Parallel print port. RS-232C serial port (2-Disk version only). Buffered input/output bus.
    Dimensions: 12-1/2 x 18-7/8 x 21-1/2″
    Power: 120VAC, 60Hz.


    what do you need to know?
    Gaming: i7-8700K, 16GB, 1TB SSD, RTX 2060, Dual 27" LG IPS Monitors.
    Vintage: TRS-80 MODEL 4, 128K RAM, 360K FDD, Gotek USB FDD, FreHD HDD, RS232-WIFI MODEM, DWP-510.
    Programmer: Dell Inspiron 660S i3-3220 with 16GB Ram, running a BK-844USB & EP-2A-88.
    Web Site: https://texastandyrestoration.com/
    Facebook Page: https://www.facebook.com/TexasTandyRestorations/

  3. #3
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    Default

    Quote Originally Posted by Patrick Bureau View Post
    TRS-80 model 4 has 2 common base versions a NON-GA (Part no. 25-1069) and GA (part No. 25-1069A) there are other variations (see Ira Goldklang's TRS-80 Web Site for complete details of all variations.

    what do you need to know?
    Thank you for your reply.

    Before I posted I had visited Ira's site and determined that I have an early Model 4: the RS-232 port faces down, the arrow keys are split to both sides of the keyboard. There are a couple of other ports which take card-edge connectors; I don't know what they are for but I'm assuming I will have to fabricate cables to fit them as OEMs are likely hard to find. But that's down the road: The first thing I need, I think, is an owner's manual, which Ira says is copyrighted and therefore does not have, and the second thing would be a service manual.

    I haven't plugged it in yet; I haven't even found the power switch or tried to figure out how to remove the case. But I plan to start with the power inlet and work my way through. Maybe it's something simple like a fuse, should there be such a thing.

    Cosmetically the machine is VGC, so abuse is not the likely cause of difficulty. I don't know whether there is a "fatal flaw", as in: "It's always the ... that fails" or "Never do ... without ... "

    Thanks again for your help.

    -CH-

    P.S. - What does "Roggled" mean?

  4. #4

    Default

    I think that was supposed to be "toggled". From LS-DOS key click sounds could be turned on or off.

    If you search you should find the Model 4 service manual online. That would be a great place to start for troubleshooting. As I recall it has a step by step troubleshooting outline. When these power on the bottom floppy drive should activate for a few seconds (red light comes on and motors on all connected drives will run). After a brief warm up the video tube will glow if the brightness/contrast are turned up (the dials under the left side of the keyboard). To enter ROM basic hold down the break key while powering on. It should display a CASS? prompt. If nothing happens at all and picture tube does not glow with brightness/contrast turned up all they way, then you would start by checking power supply, power switch, related wiring and the power cord. If the picture tube glows but drive does not run then you have power to the video at least but a bunch of other things could be a problem. Mostly these things hold up quite well and a lot of the problems are basic involving connections for the various cables being dirty. Some cables (like the cable connecting the floppy controller to the motherboard) were a low cost design and can be pretty fragile with age so use care or be prepared to replace. A common thing is the filter capacitors on the power supply burning out when aged and that makes a lot of smoke but generally doesn't affect the machine otherwise working.

    Be careful taking it apart as the picture tube is easy to break the back off of. Shine a light in the vents on top and take a look. What I do is flip it upside down, remove the screws, flip it back over while being careful to support it so it stays together. Then lift the top off but try to pull it forward while lifting (gently) so the rear of the picture tube does hit not the shielding behind it. There can be wires that get tangled as well. Peer down the vents while doing this to watch the rear of the tube. Once lifted up enough the top can be put on its side to the left of the unit and the wires to the video board will remain connected. You can work on it and test with it like this. Youtube may have some videos of this procedure as well.

  5. #5
    Join Date
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    Chaffee, MO
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    Default

    CH,
    Sent you PM. If you have the Tandon TM-100 Floppy Drives Open the Door and look for two White short
    Nylon Pins in the Hinge Points. If you have any of those pins, replace then with some full length Brass Rod
    as those white Pins cause the Hinge assembly to break. If you have Broken Hinge parts, those parts are
    on ThingIVerse and can be 3D printed. I can send you 2 or 3 to fix your Tandon for minimum cost.

    Biggest thing to do is change Rifa Caps (large Square Caps) on Power Supplies. (Tandy and Astec)
    Re-Flow Fresh Kester 63/37 Solder on Pins of Tandy Power Supply. Clean Floppy Head Guide Rods
    with Alcohol, and relube with about 3-4 drops of Dri-Slide (a motorcycle lubricant that does not attract dirt.)
    http://www.akhara.com/trs-80/psrepair/index.html

    Boot to Cassette Basic the first power on, so you have some characters on screen to adjust Brightness and
    contrast. Those controls are on left side bottom, and can be felt if you stick fingers of left hand under left side
    and slide towards rear of computer. Set Brightness so you can just see the Characters good, and then adjust
    contrast. Power switch is about same position on right side, under bottom.

    Other than that they are pretty bullet proof.

    Larry
    Last edited by ldkraemer; January 15th, 2020 at 06:56 AM.

  6. #6
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    Default

    Larry,

    Thanks for your input. I also found some docs on eBay. Hinge pins appear to be metal, perhaps brass.

    I turned the machine over once again and found the brightness and contrast pots on the left hand side (as upright) and the power switch on the right. I also located the screws for releasing the case; it looks like the base stays put and the top lifts off.

    So I plugged in and found that the drives lit when power was applied and a seek occurred on the lower drive. I put in a blank floppy and repeated the experiment with the door closed; although there was no boot there was no smoke, either. After a bit the drive stopped - still nothing on the display - but started to spin again after a brief while. After fiddling with the contrast and brightness controls I got a pretty crisp-looking display that was flashing with the values in the attached picture.

    I'll try the cassette boot next and report back. I'm happy to have any results so far, but eventually I'll need to create some OS disks.

    Thanks again to all for their suggestions.

    -CH-

    TRS80_Model4.jpg

  7. #7

    Default

    Could be a bad disk.

    Try holding down BREAK when powering on to get into ROM basic. Just hit enter at the CASS? and Memory? prompts. Should get a Ready prompt. This would at least confirm basic function of the motherboard.

  8. #8
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    Default

    Briefly: Holding down the BREAK key caused the machine to prompt: CASS? after power was applied. With a cleaning disk in the A / 0 drive I got a message DISKETTE ?

    That's all the more progress I have made, except for downloading system disks from Dave Dunfield's site. But, as was often repeated in "Lawrence of Arabia", nothing is written.

    Thanks again for everyone's input. I've still got a lot to learn.

    -CH-

  9. #9
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    Default

    CH,
    Yes, when you see the Cass?? Prompt there are two possible answers. L for LOW = 500 Baud
    and H for HIGH = 1500 Baud for the tapes baud rate. Or you can just hit the ENTER key twice
    and you will be at Cassette Basic.
    If the FDC is working and Memory is good you can load and save Basic Programs to a formatted Floppy.

    I'd recommend to Replace the Rifa Caps ASAP. If they have hairline cracks they will blow. The machine
    will still run fine, but it makes a mess and lots of smoke.

    It's a good thing the Floppy's have Brass full length pivot pins. That will help save the hinges.

    Larry

  10. #10

    Default

    Quote Originally Posted by clh333 View Post
    Chuffed by the resuscitation of a Model 100 and a Model 102.....
    What problems did you encounter?

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