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Fixing a Tandy Caveman...

 
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Tupin
Tomy Blip


Joined: 26 Apr 2012
Last Visit: 27 Apr 2012
Posts: 4

PostPosted: Thu Apr 26, 2012 6:54 pm    Post subject: Fixing a Tandy Caveman... Reply with quote

So, I was really excited to get my first handheld, a Tandy Caveman. I used a 6v universal power supply to power it up, which worked for a little bit, but then it stopped working, the VFD screen fading as I used it. Eventually, there were only red lines and now nothing.

What should I be looking for on the inside to fix? Blown transistors? Anyone fix one of these before?
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Tupin
Tomy Blip


Joined: 26 Apr 2012
Last Visit: 27 Apr 2012
Posts: 4

PostPosted: Thu Apr 26, 2012 7:22 pm    Post subject: Reply with quote

Huh, it started working again. There's still a problem, though. The characters are sort of messed up, some of the caveman frames are lit up when they shouldn't be, and other weird stuff with the eggs/dinosaur.

No idea what's causing this...
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Rik
Site Admin


Joined: 07 Oct 2005
Last Visit: 24 Aug 2014
Posts: 1728
Location: California

PostPosted: Fri Apr 27, 2012 12:18 am    Post subject: Reply with quote

Might be a weak power supply... What the amps on it? Sounds like it might be having difficulties.

If it's adjustable, try it at 9volts. The games can handle 6-9 volts with no problem.

Or try a different one, or batteries if you have them, just to confirm if that's the problem or not...

If it's still acting weird, I'd go after the transistors first... There's a repair guide here:
http://www.handheldmuseum.com/Coleco/ColecoRepair/index.html
for Coleco games. Start looking at page 2, the circuitry in most all VFD based games is pretty much the same, so you can still use this is a general guide on what to look for...

Rik
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blanka
Adventure Vision


Joined: 14 Dec 2010
Last Visit: 27 Aug 2014
Posts: 446
Location: Eindhoven, the Netherlands

PostPosted: Fri Apr 27, 2012 7:33 am    Post subject: Reply with quote

Measure the voltages. What chip does it have? A 38800?
Then pick a multimeter, attach the black wire to the neg pole of the batteries/adapter, set it to DC 200V range, then measure with the red wire
Pin 14 should be between -25 and -30V
Pin 16/17 should be -10V

Then switch to AC 20V range.
Measure the voltage over the outer pins of the VFD (first and last), it should measure 2-3V

If you find these values, the power supply is OK.
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Tupin
Tomy Blip


Joined: 26 Apr 2012
Last Visit: 27 Apr 2012
Posts: 4

PostPosted: Fri Apr 27, 2012 12:47 pm    Post subject: Reply with quote

It works with batteries, but the graphics still are messed up.
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Tupin
Tomy Blip


Joined: 26 Apr 2012
Last Visit: 27 Apr 2012
Posts: 4

PostPosted: Fri Apr 27, 2012 12:57 pm    Post subject: Reply with quote

It is an NEC D553C.
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