Dodgy IBM PC Convertible power supply

Randy McLaughlin cctalk at
Mon Jun 13 12:32:49 CDT 2005

From: "Vintage Computer Festival" <vcf at>
Sent: Monday, June 13, 2005 12:06 PM

> I've got a couple IBM PC Convertibles that exhibit the same problem with
> their power supply.  When I press the power button (which is a momentary
> switch) it turns on briefly: the disk drive light goes on and the drive
> starts to spin or the display shows brief activity, but in either case for
> only about a tenth of a second.  Sometimes if I hold the switch just right
> I can get it to make it through the entire memory test and up to the point
> where it wants a disk in the drive, but it's very hit & miss.  It
> certainly is not behaving as it should.
> I've tried cleaning both the switch and the AC adaptor socket but so far
> this has not improved anything.  The switch seems to be doing its job, and
> the power seems to be making it to the unit.  It just seems like the power
> supply becomes unhappy at some point, unless I hold the switch in a
> certain position, but then I invariably lose my touch and the power goes
> out again.
> I'm using appropriate adaptors, including a car cigarette lighter adaptor
> plugged into mains using an AC-to-cigarette lighter socket adapter (kind
> of handy in this case).
> I've tried swapping the internal power supplies around between units but
> get the same problem on each.  One has a battery pack and one doesn't, but
> having it in or not in does not make a difference.
> Seems like the power supplies are dodgy or something?  Any ideas?
> --
> Sellam Ismail                                        Vintage Computer 
> Festival
> ------------------------------------------------------------------------------
> International Man of Intrigue and Danger 
> [ Old computing resources for business || Buy/Sell/Trade Vintage 
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My methods are simple:

Mechanical failure composes the majority of the problems (bad connections):

Check - plugs, sockets, switches, connectors, and cold solder joints.  Use a 
cleaner that works like Tarn-X, check for loose sockets.

The fact that you say "unless I hold the switch in a certain position" makes 
me suspicious about how clean it is.

I am unfamiliar with the convertible PS but if you have a schematic I would 
look for the logic switch that is supposed to latch it and follow that path.

The majority of the time repairs are as I said a mechanical failure, with 
age tarnished connections are common.


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