[sebhc] H90

Barry Watzman Watzman at neo.rr.com
Fri May 11 14:45:29 CDT 2007

While plugging in a connector wrong is certainly possible, Tantalum caps
will also blow after prolonged periods of storage if the slightest bit of
humidity got into the capacitor.

I've had it happen to boards dozens of times, very common.

Barry Watzman
Watzman at neo.rr.com

-----Original Message-----
From: sebhc-bounces at sebhc.org [mailto:sebhc-bounces at sebhc.org] On Behalf Of
Lee Hart
Sent: Friday, May 11, 2007 2:02 AM
To: sebhc at sebhc.org
Subject: Re: [sebhc] H90

Robin England wrote:
> 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.

I find that blown tantalum caps usually means that someone plugged in 
one of the I/O board up/down off by a pin. This can also blow one of the 
on-board regulators (the -12v and -5v ones seem most vulnerable).

So, replace the capacitors and check the voltages from the regulators 
along the top of the board to be sure they are all working.

I would get the CPU board working by itself, without any memory or I/O 
boards to confuse things. You'll have to set the DIP switches 
accordingly. If you had a Z89-37 or other disk controller with dangling 
cables to the CPU board, you'll have to pull that cable and replace the 
missing chips on the CPU board for it to work without that disk controller.

Likewise, if you remove an expansion memory memory board, you'll have to 
remove its flat cable and re-install the missing chip where it plugs 
into the CPU board.

Ring the bells that still can ring
Forget the perfect offering
There is a crack in everything
That's how the light gets in    --    Leonard Cohen
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net
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