[vcf-midatlantic] Repairs to a Heath WH19 Terminal

Matt Patoray mspproductions at gmail.com
Sun Mar 12 13:15:53 EDT 2017


Jason,

Pull the HOT and try to power it on, and see what the current draw is then. 

Sent from my iPhone

> On Mar 12, 2017, at 12:37 PM, Jason Perkins via vcf-midatlantic <vcf-midatlantic at lists.vintagecomputerfederation.org> wrote:
> 
> Looking for some advice on getting a Heath WH19 terminal going again.
> 
> First, some schematics:
> 
> http://www.rsp-italy.it/Electronics/Kits/_contents/Heathkit/Kits/Heathkit%20H-19%20video%20terminal.pdf
> 
> My annotations on the x-ray view: https://goo.gl/photos/PF8N7wRDPLc1czUU7
> 
> What I observed:
> When first powering the terminal it did nothing. The fast blow 1A fuse was
> open, the wire was broken. As it was handled it broke more, suggesting it
> could have simply failed from vibration? The manual said that a 2A slow
> blow fuse is appropriate for 120v operation.
> 
> I replaced the fuse with the smallest one I had on hand, a 4A slow blow,
> connected the terminal to a current meter, and powered it up. It beeped :)
> But was drawing 5A :( and then there was a little smoke :( :( I quickly
> powered it off.
> 
> R263, a 1.2 ohm 2W resistor had cracked. R263 supplies the +53v rail to the
> horizontal section.
> 
> C228 seems to be good (open resistance, correct mfd), D208 and D211 seem to
> be good (.5v one way, open the other), C229 isn't shorted but my meter
> can't measure its capacitance.
> 
> I replaced R263 with a 4w 1.2 ohm resistor I had on hand, and powered up
> again. Still too much current draw, and more smoke in the area of Q217.
> 
> Does this suggest Q217, the HOT, is bad? I pulled it out and did the diode
> test on it, it seemed to test OK? It's a BU500, and I see some NOS ones on
> ebay.
> 
> I'm unsure what my next step should be.
> 
> Thanks for your input!
> 
> -- 
> Jason Perkins
> 313 355 0085



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