[sebhc] H90

[Robin England]

Hi Carroll

Bearing in mind the blown caps I would go straight for the ROM(s) on the CPU 
board. The earlier TI chips were always quite vulnerable to a bad +5 supply.

Robin

----- Original Message ----- 
From: "Carroll Waddell" <carrollwaddell at sc.rr.com>
To: <sebhc at sebhc.org>
Sent: Friday, May 11, 2007 1:30 AM
Subject: [sebhc] H90


> Does anyone have any troubleshooting experience on Heathkit H89? I bought 
> 2 (neither will work) hoping to be able to repair and keep at least one.
> I've swapped the terminal logic board with the one in my H19 terminal, so 
> I know the TLB is ok. The CPU board had several blown tantalum caps, and 
> I've replaced those. All the voltages check out ok with little to no ac 
> ripple. With a scope, I can see activity on the address and data lines but 
> I still get no display on the CRT (except the blinking cursor). The TLB 
> does give 1 beep when the power is turned on. (The same thing my H19 does)
> It's difficult to troubleshoot when the only thing visible is suppossed to 
> be on the CRT screen.
>
> I suppose it could be in the serial port interface.
>
> Anyone else have any ideas?
>
> Carroll
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