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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 28th Nov 2020, 8:56 am   #1
GaryBrigden
Diode
 
Join Date: Nov 2020
Location: Minehead, Somerset, UK.
Posts: 2
Default Sharp PC-1500 not working

Hello,

I have acquired a Sharp pocket Computer 1500, with 4 colour plotter.

When pressing the ON button, the LCD flashes and then fades to nothing, and the keyboard is unresponsive.

If I press the reset, the LCD flashes again, then fades and as I release the reset, the same behaviour.

Has anyone had experience with these little devices and might recognise this?

I suspect something has blown, but where to start?

Many thanks
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Old 28th Nov 2020, 4:50 pm   #2
Slothie
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Join Date: Apr 2018
Location: Newbury, Berkshire, UK.
Posts: 723
Default Re: Sharp PC-1500 not working

I've no specific knowledge of these, but I have repaired a few old calculators. I would start off carefully dismantling it (there's probably a youtube video - look for Tandy PC-2 as well which is rebadged model) cleaning it out and look for signs of corrosion - only a tiny bit can cause shorts. There's also a couple of electrolytic caps from what I can see in photos which could cause problems in the usual manner. The ICs in calculators from this period seem to be pretty reliable, so I would look at the other components.
Its also possible the crystal is damaged, with no clock nothing will work and they are susceptible to damage.
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Old 28th Nov 2020, 5:08 pm   #3
TonyDuell
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Join Date: Jun 2015
Location: Biggin Hill, London, UK.
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Default Re: Sharp PC-1500 not working

As Slothie said, the Tandy/ Radio Shack PC2 is a close clone but with a diffferent keyboard layout. The circuitry is much the same and the service manual for that is on the web.

I have the offiical Sharp technical reference manual on my bookshelf but that's more about machine code programming and interfacing than repairing the machine. I will look to see if there's anything of interest though.

The 2 large ICs on the lower PCB are the processor (LH5801) and I/O (LH5810 or LH5811). Also in there are RAM (if this is a plain PC1500, it's CMOS 2114-a-like things I think), a system ROM, etc.

I have had the I/O controllers fail, but the machine would normally still power up. Just an electrical row or column of the keyboard would be dead.
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Old 28th Nov 2020, 11:00 pm   #4
GaryBrigden
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Join Date: Nov 2020
Location: Minehead, Somerset, UK.
Posts: 2
Default Re: Sharp PC-1500 not working

Hi,

Thank you for your replies.
I have ventured to taken the unit apart, and all looks fine with the soldering and surprisingly looking in good health generally.
I suspect the power regulator to be the issue. In this unit it is a 14pin resin based chip that controls a host of things around power.
I am looking for the part online but think it is a Sharp component and not readily available so may have to butcher another 1500 for one.

Thanks
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