HP 2100 cpu plea

From: Bob Shannon <bshannon_at_tiac.net>
Date: Sun Jan 19 13:00:01 2003

Oh yes, check the ripple FIRST!

I've strongly reccomended this to you before, its essential.

If the filter caps are really weak, you may see the ripple even with
your scope set for DC coupling. This
will of course appear as a low-amplitude sine wave riding ontop of the
DC voltage. You can keep increasing
the vertical gain, and moving the trace downwards (for a positive supply
voltage) so your only looking at
the AC component. But at some point, you will run out of vertical
position adjustment control range to keep
the display on-screen.

At this point you must use AC coupling to increase the vertical gain.

Flakey core memory that does not have bad bits or addresses is most
commonly due to incorrect power supply
voltages or current limit adjustments. Ripple in the memory supply
voltages falls into this general catagory.

If your less than comfortable with the scope measurments on a linear
power supply, you can try temporarily adding
an external filter cap in parallel, but this is often inconclusive.
 See, if the original part is leaky, simply adding more
capactiance may not eliminate the problem. But if the ripple is more
due to a loss of capacitance than leakage (uncommon, but it happens)
then adding the parallel capacitor will show a large reduction in the
ripple. If this is
the case, you must replace the original filter cap.

If adding the external filter cap shows no reduction in measured ripple,
then there is little question that the original part is leaky and
needing replacement.

So this generally less-than-ideal trick might shed some light in your
particular case.

Jay West wrote:

>No, the I/O system is fine, it's just the memory section that is flaky. When
>I said IOP I meant the I/O processor, meaning the other 2100 cpu in the
>system (2000/Access uses two cpu's, one called the "system" cpu, the other
>called the "I/O Processor" or "IOP" cpu. Both are regular 2100 cpu's. Just
>so happens the system cpu on mine is a 2100A, the IOP cpu is a 2100S. And,
>it's the 2100S that has bizarre memory problems.
>I'm not that great with electronics... but I'm at my wits end. Spent so much
>time on it I can't seem to see the forest for the trees. Hell I don't even
>know where to start now. I have checked the PS levels, and they seem fine.
>But what I have never checked is ripple on the power supply outputs, I think
>core memory can get rather touchy about that. I think you just hook your
>probe to the output and set AC coupling mode to see just the AC component,
>and look to see how far the ripplyness swings off the baseline? That may be
>the simple thing to check first. *sigh* I dunno. I do have the complete
>diagrams manual for the system which includes schematics, but not enough
>electronics ability to really make use of it.
>So how goes things in your world? Was the job hunt ever fruitfull? What's
>your current classic computer projects these days, yours are always
>interesting! I haven't forgotten about that 11/34a up there either... just
>looking for the right time to work that out if you're still willing. Thanks
>for any advice on the 2100!
>Jay West
>----- Original Message -----
>From: "Bob Shannon" <bshannon_at_tiac.net>
>To: <cctalk_at_classiccmp.org>
>Sent: Sunday, January 19, 2003 8:15 AM
>Subject: Re: HP 2100 cpu plea
>>Last I heard, your memory section was flakey. Now the I/O system is not
>>What exactly is the problem?
>>I've never been impressed with the HP2100A's, but we should be able to
>>figure out whats wrong
>>and fix it.
>>The biggest problem is going to be finding replacement chips, as much of
>>the machine is not TTL. But if we
>>can narrow it down to a board or chip, I think we can get your CPU
>>running again.
>>Jay West wrote:
>>>Ok folks, I'm officially desperate. I can't figure out what is wrong with
>>>the 2100 IOP cpu memory section on my 2000/Access system. So, just
>>>I'd post this to the list....forgive my begging, it isn't pretty *Grin*
>>>Anyone have a working HP 2100 cpu available? I will pay real $$$ at this
>>>point, or trade probably just about anything I have for one. If anyone
>>>one they will sell, or trade for, or give away to a place (me) that will
>>>actually use it and not throw it on a shelf, I would like to know. I'd
>>>welcome any leads as to where one might be stored, etc. Or, as an
>>>alternative, if anyone has a magical device that will instantly transfer
>>>of Tony Duell's repair knowledge and ability to my brain, that might work
>>>FYI - I need either a 2100A or 2100S cpu. Don't need or want any 21MX or
>>>1000 type cpus.
>>>[This E-mail scanned for viruses by Declude Virus]
>[This E-mail scanned for viruses by Declude Virus]
Received on Sun Jan 19 2003 - 13:00:01 GMT

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