15 May
2012
15 May
'12
11:35 a.m.
On May 14, 2012, at 3:51 PM, Rob Jarratt wrote:
I wil labsolutely agree _if you are going to use it_. If you are planning
on doing hardware reparis, if you are going to want to fix PSUs,
monitors, disk drives and other analogue stuff, then you need a 'scope.
Equally, it would be a total waste of money for somebody who nefver pulls
the covers on anything.
I have a H7140 that I am *still* trying to repair
after more than a year of
failure and despite the valiant attempts of one person on this list to help
me, and it is in much better condition than the one in the pictures.
However, I am hampered by my poor knowledge of PSUs (which is gradually
improving), my slowly developing desoldering skills, and my unwillingness to
spend a lot of money on oscilloscopes, bench PSUs, ESR testers and goodness
knows what else.
Well, I'll gladly tell you to spend some money on a decent scope. You will come to wonder how you ever got along without one,
even if it's a 2-channel
analog scope with relatively low bandwidth. They're so useful for so many
Don't buy more than you need (or think you might need). It's rare for
callsic comptuer repairs to need more than 50MHz bandwidth in a 'scope.
And rememebr than an old 50MHz 'scope is still a 50MHz 'scope.
What I mean b ythat is that it is often better to buy a good second-hand
instruemnt which meets the spec than a new one with better on-paper spec
and more features which turns out to be unreliable, unsupported, and
actualyl doesn't meet that spec (Seen 'em all...)
things; I promise you won't regret it (as long as
you don't go bargain-
hunting and find one that you also have to fix).
Or unless you like restorign test gear as weil as classic computers ;-)
If you only need 5v or 12v, AT power supplies (or
jury-rigged ATX ones)
make reasonable ones. I'm willing to bet you have at least one of those
lying about. :-) My 11/23, for example, runs off an AT supply (though
its rather thin wires tend to get warm, so one of these days, I'll make
the upgrade to a decent enclosure). Most AT supplies also offer -5v and
-12v, should you need them.
The H7140 PSU is not an easy thig to substitute. The main supply rail is
+5V and 120A (or is it 125A, anyway it's large). There are also +/-15V
(not 12V) rails and separate +5V, -5V, +12V and -12V suppleis for the memory
In any case,the PSU is a part of the original hardware design and should
be kept as such. To do otherwise is like replacign the CPU with a PC
running an emulator. It's not the original machine any more.
-tony