Datavue 25 Lunchbox PC Power Supply Repair

(This was originally a Twitter thread from May 7, 2019.)

May 7, 2019

New addition: Datavue 25 portable lunchbox PC. Keyboard stows on front, two 3.5 floppy drives, 13 pounds.

The screen pivots upward out of the case, presumably for a better view. I don’t know yet, it won’t power up. The power supply goes into the battery compartment.

Fuse was blown inside the power supply. I replaced it and it blew again. Nothing looks visibly bad to me. Some slight discoloration (old flux?). Bad cap(s) perhaps.

May 8, 2019

A tip from @UpLateGeek suggested the bridge rectifier as a starting point. I metered it in circuit and two adjacent pins are shorted in both directions so it may have failed. I have this spare BA20 but can’t find what the marking mean (E5A vs C3G). Thoughts?

May 9, 2019

Swapped in the new BA20 bridge rectifier. (One side was bad in the old one.) On the advice of @anachrocomputer I also checked the two switching transistors. All pins are shorted together. NTE379 looks to be a replacement for C3159.

May 13, 2019

Parts are in for the DataVue 25 power supply. These NTE379 will be stand-ins for the C3159 switching transistors.

Carefully bent the legs, added extra heat sink compound, and screwed them down. Put it all back together and tested. Voltages at 13.3V which I think is OK without a load. But will it power the DataVue 25 portable?

It works! Look at that screen! I don’t think I’ve seen yellow on red of this gas plasma display. Apparently this machine has a built in RAM disk function. Is that common on early DOS machines?

It also includes a resident dumb serial terminal in ROM. A key press brings it up instantly anywhere. That’s going to be really handy to have.

May 15, 2019

The DataVue 25 supported an external floppy drive as a “backpack” add on. Presumably it connected to this 34 pin connector. I assume this supplied power too? No pinout in the manual. It would be great to connect a Gotek floppy emulator here.Any guesses?

Do you have a DataVue 25 or similar lunchbox PC? Let me know in the comments!

One thought on “Datavue 25 Lunchbox PC Power Supply Repair

  1. Permalink  ⋅ Reply

    Hak Fo

    February 25, 2023 at 1:55am

    This must have been offered in multiple versions. I had one many years ago from a jumble sale and it had a non-backlit screen and a single 360k drive. The expansion bus connector always looked tempting, because it seemed like exactly 62 pins, suspicious… but I never dared to try to connect an ISA card.

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