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Thread: Model 4D keyboard

  1. #1

    Default Model 4D keyboard

    I thought Radio Shack switched back to the Alps keyboard for the Model 4D, but I recently picked up another one and unlike my other Model 4D with the Alps keyboard this one has a membrane keyboard. It's definitely a 4D keyboard as it has the Backspace key.

    The new 4D does work but liquid was spilled on it at some point. There's corrosion on the plate that has the power cord and cassette connector on the inside and on the left and middle of the board at the top (as you are looking at it from the back). I haven't taken the circuit board out yet to check further as I'm going to discuss with the seller first.

  2. #2
    Join Date
    Sep 2011
    Location
    Melbourne, Australia
    Posts
    910

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    I've mentioned it before but it bears repeating that early 4Ds came with a version of the membrane keyboard that was in the Gate Array Model 4. Some time after the the 4D was out for a while (around serial number 16000) they must have ran out of membrane keyboard and went back to ALPS to make the keyboard for the last batch of 4Ds. That's how I see it anyway... I'd imagine if TCA needed another, say, 10,000 keyboards they would put the tender to several keyboard manufacturers and in this instance ALPS got the job.

    What are the serial numbers of your two 4Ds, I'd be interested to know if the one with the membrane keyboard is significantly lower than that of the ALPS unit?

    Ian.
    *There is never a charge for Tech Support even if you don't purchase from me - We are Enthusiasts Helping Other Enthusiast and that is just the way it is

  3. #3

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    Quote Originally Posted by TRS-Ian View Post
    I've mentioned it before but it bears repeating that early 4Ds came with a version of the membrane keyboard that was in the Gate Array Model 4. Some time after the the 4D was out for a while (around serial number 16000) they must have ran out of membrane keyboard and went back to ALPS to make the keyboard for the last batch of 4Ds. That's how I see it anyway... I'd imagine if TCA needed another, say, 10,000 keyboards they would put the tender to several keyboard manufacturers and in this instance ALPS got the job.

    What are the serial numbers of your two 4Ds, I'd be interested to know if the one with the membrane keyboard is significantly lower than that of the ALPS unit?

    Ian.
    The 4D with the membrane keyboard is serial number 009444. The white sticker above the nameplate on the bottom has 6UAA693. The 4D with the Alps keyboard is serial number 012978. The white sticker on that one has 5UBA693.

    Does anyone know what the code number on the white sticker is for?

  4. #4

    Default

    I noticed both 4D motherboards have extra wiring added over the 4 GA motherboard (comparing my two 4D motherboard with my three 4 GA motherboards). Does anyone know what issues the extra wiring addresses? If not I'll try mapping them out.

  5. #5
    Join Date
    Jun 2015
    Location
    Sioux Falls SD
    Posts
    158

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    What revision motherboard? Some early 4Ds had Rev B and others Rev C. Rev B had wire jumpers for RAM expansion.

  6. #6
    Join Date
    Sep 2011
    Location
    Melbourne, Australia
    Posts
    910

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    We really need a picture of the motherboards. Remember there is very little difference between the 4GA and 4D motherboard, mainly to do with how the 64K/128K upgrade is done (JP13 jumper on the 4D vs. wire unsolder/solder on the 4GA).

    As far as Tandy repair centre is concerned, the 4GA/4D motherboards are interchangeable so if someone came in with a broken 4D and all they had on hand was a 4GA board they would sub that in to get the system back up and running quickly, esp. if the computer was under the extended service agreement plan.

    Ian.
    *There is never a charge for Tech Support even if you don't purchase from me - We are Enthusiasts Helping Other Enthusiast and that is just the way it is

  7. #7

    Default

    Quote Originally Posted by TRS-Ian View Post
    We really need a picture of the motherboards. Remember there is very little difference between the 4GA and 4D motherboard, mainly to do with how the 64K/128K upgrade is done (JP13 jumper on the 4D vs. wire unsolder/solder on the 4GA).

    As far as Tandy repair centre is concerned, the 4GA/4D motherboards are interchangeable so if someone came in with a broken 4D and all they had on hand was a 4GA board they would sub that in to get the system back up and running quickly, esp. if the computer was under the extended service agreement plan.

    Ian.
    I'll get pictures this weekend.

    I need to verify but I think at least two of my 4GAs have the jumper instead of the wire for the memory upgrade.

  8. #8

    Default

    I haven't gotten pictures of the different motherboards but I thought I'd post pictures of the corrosion:

    Model 4D - 4.jpg
    Model 4D - 3.jpg
    Model 4D - 9.jpg
    Model 4D - 10.jpg
    Model 4D - 8.jpg

    I'm not sure what spilled down in it but there's some odd looking debris, too.

    It's going back. I'm guessing the seller will relist it.

  9. #9

    Default

    I'd bet it sat in a barn or outside and was pissed on by a critter. I don't think it was submerged in water.

  10. #10

    Default

    I ended up keeping the 4D and got a partial refund. I completely disassembled the bottom assembly and tossed the corroded frame (which also had the side cut out of it but I don't know why that was done), scrubbed out the plastic, cleaned the motherboard, and reassembled it. I had a dead Model 4 that served as a parts donor for the frame and I built a replacement floppy cable and replaced one drives. Once I got it all back together I connected the upper assembly and it worked.

    After verifying it worked I disassembled the upper assembly to clean it. There was some dirt that was noticeable along the back edge behind the CRT board so I wanted to clean that up. There was a dead bee between the CRT board and the plastic insulating sheet. There was also a spot of something on the CRT board itself that might have been honey. I cleaned the CRT board, plastic sheet, and aluminum mounting sheet, and CRT. I then reassembled the upper assembly and connected it to the bottom assembly.

    When I power it up I don't get anything on the display. I can turn up the brightness and see the raster. I've checked all the connections and there's nothing lose or disconnected. I connected the display from the donor machine and that works. I didn't change any of the pots on the CRT board or get them wet (I cleaned off the substance carefully with alcohol). There's a glow in the neck of the CRT when it's powered on.

    Any ideas? Worst case I can swap the nameplate from the 4D to the donor upper assembly and use it or swap the CRT and board. They both use the same CRT board, but different CRTs. Interesting the CRTs are mounted 180 degrees off in each one. The 4 has the anode on the drive side and the 4D has the anode on the other side.

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