Dead TechStep

[Elemenoh]

After years of searching, I've finally scored a TechStep. Unfortunately it shows no power with a good 9V battery. I haven't ordered a power supply yet, but suspect it'll produce the same result.

Nothing is scorched and so far all of the joints I've checked look okay. However, 9V is not making its way from the daughter board to the DC/DC converter (U3) on the main board. And there is no voltage across the GND and +(9?)V pins of the daughter board. Continuity is okay from the 9V battery input through the caps and inductors.

There is what looks like good resistance across C1m, C2m, C3m and C4m. I haven't checked those with an ESR meter yet but they're tants/polys and visually look okay. The inductors are short across their pins. There's so little to this circuit that I'm stumped as to what's wrong.

Any ideas for what to check?

 

[Elemenoh]

While double-checking the connections from the battery and barrel, I noticed the ribbon cable was a bit too wiggly. After pulling lightly I found the battery positive connection was broken. Hopefully reattaching that will fix the issue.

 

[splorp]

Thanks for sharing this … I’m wondering if this is the same reason my TechStep doesn’t power up?

 

[Elemenoh]

The power jack is center negative. I expected something to be blown from someone connecting a more typical center positive adapter. I don’t think there’s any protection against that. hopefully all this needs is to have these wires reconnected.

@splorp Have you opened yours up yet?

 

[splorp]

Not yet. Something I plan on doing this week, though.

 

[Elemenoh]

I replaced the ribbon cable with one that's a touch longer. The TechStep still does not display anything on screen and still doesn't show voltage at the voltage regulator. Back to trying to following the path from the battery more closely.

 

[Elemenoh]

It powers up with a power adapter but still not with the battery. It’s probably something simple on that DC-in board but haven’t been able to figure it out yet. Anyway, this is good enough for now

 

[LeadedSolder]

Great work so far! Does the “ROM B” button allow you to select a second ROM with more machines on it?

 

[Elemenoh]

My ROM B has generic SCSI tests on it.