Troubleshooting TRS-80 Model 4 & NEC Multispeed EL

Hi, so, I wasn't really sure where else to post about this. I got these two devices from a thrift store with the intent of restoring them (eventually). I'm in the early stages.

So, the TRS-80 Model 4 (not the CoCo). In the store, I plugged it in, turned it on, and the floppy drive made a few little read noises, then the CRT came on with the prompt "Cass?" This seemed promising, so I took it home. I'm not sure if I broke something in transit, but when I plugged it and turned it on at home, floppy drive 0 immediately just started this horrible churning noise, like it was spinning nonstop (there is no media in the drive). When the CRT came on, it said "Diskette?" So, basically, I'm wondering if anyone has heard of this sort of problem before, or has any idea what it might be. (Or perhaps it's not even a problem, and it's supposed to sound like that? Like I said, early days, but it sounds horrid. If this behavior is normal, then I have no idea what I did to prompt it to try to read a cassette initially in the store.) I am having trouble finding info about this model. Perhaps it's just waiting for a system disk, which I sadly don't think I have yet; there is a mysterious floppy in drive 1, but I'm afraid to put it in drive 0 for fear of damaging it, and I don't have anything else with a 5.25" drive right now.

As for the NEC Multispeed (an IBM-compatible portable with an 8086 clone processor), it did not come with a charger and I have no idea if it is at all functional. It says to use only a 13.5v 1.5a charger. I scrounged around the house and the closest I could come up with were 12v 2a and 12v 1.5a. Neither one seems to do anything. So my question is, can I rule out the charger as the problem? I don't know much about electrical engineering. Or, will I not know whether the problem definitely lies with the computer itself, as I suspect, until I get a charger that matches the specs exactly?

Thanks for reading!


  • I can't tell you about the NEC, but as for the TRS-80 I could say that the noise comes because the floppy is obviously spinning the wrong way. I recommend you to open the PC, and take out the floppy that makes noise. Clean it up and see if is there any visible problem with it.

  • Didn’t the TRS-80 model 4 still use those full height tandon drives? Those can be quite noisy. They can also get dirty and jammed up.

    You should disassemble it and give the unit an initial cleaning.

    Tandon drives are fairly easy to clean. The more common problems in drives that have been sitting around include dust on the track zero sensor, dust caked on the drive rails preventing the heads from moving (clean the rails and apply some fresh lithium grease), rusty stuck stepper motors (the heads should move freely along the rails when no power is applied), and dirty heads (use a q-tip and alcohol to gently clean the tops of the heads).

    Anyway, there is lots of information about the model 4 machines out there, you will just need to read up on them. We don’t have much TRS-80 software on Winworld, but if we did it would be limited to commercial products.

  • edited July 2018

    For the NEC, be careful with using random power supplies on these older laptops. Both my old Sharp and Zenith laptops require supplies with a center negative barrel plug. Using a power supply with the wrong polarity might spell disaster- although since you didn't describe any smoke or popping noises, perhaps you didn't cause much of any harm.

    The symbols on both the power supply and laptop should match.

  • To get the "Cass" prompt on the TRS-80 M4 with disk drives installed:
    Hold down the [BREAK] key whenever you turn on or RESET the computer.

    The computer will now start in ROM BASIC.
    The following message appears:
    "Cass?" (Press the [ENTER] key in response}

    The next message then appears:
    "Memory Size?" (Press the [ENTER] key in response}

    After responding to these two questions, ROM BASIC starts with the following message:
    Radio Shack Model III Basic
    (c) '80 Tandy

    You can find software and manuals for the TRS-80s at:

  • edited July 2018

    Thanks so much, everyone! Now to find the time to do research and open them up. :)

    Ack! there's no polarity indicator on the laptop, but digging through Ebay listing photos, it turns out that the original charger is indeed negative polarity. I guess this increases the likelihood of going with plan B and turning it into a completely ridiculous raspberry pi laptop.

  • Haha yeah. Lots of ectronics won't come close to running if you don't put exactly the right voltage, which also reduces the damage/change you probably did.

    Just ask my dcs420. The battery is shot and so is the charger. I spend 2 hours trying to strap a 9v supply to the battery jst socket. Nothing. Hook up some 9.6v power supply and battery from dodgy ebay seller... Images my phone could surpass.

    However, found some quality reading. Looks likesomeone else tried to power one on. Tldr, check fuses and the battery. I'd bet a tripped fuse.

    For the power supply, if you find the barrel dimensions of the jack, you could grab a negative tip power supply from another dodgy chinese seller and it'd work.

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