Tothwolf asks:
>Are the two fans on the side of the power supply running properly?
Both still seem to be. However, most of the tests I'm talking about are run
with the lid off, and a small floor fan set up to blow over the mainboard
(in the same direction as the small cooling fans). I think the airflow rate
>from this is much higher than the cooling fans would generate, but may not
be in the right areas.
>What type of hard drive do you have in the system?
1-Gig RZ26L.
>Your mainboard may have a bad solder joint somewhere near the comparator,
>which would explain the thermal issue. That tends to be the worst type of
>problem to pinpoint too.
It would, but unless the comparator or one of the voltage-divider resistors
is intermittent, I'm at a loss to explain the varying voltage on the
comparator input. I have physically shoved back and forth on all 3
components while it was running, no effect. Also I can't *see* any bad
solder joint, but then I can barely see the two resistors anyway.
>First you'll want to remove lower portion of the plastic shell. There are
>5 screws on the bottom of the unit,
5 holes, only two screws left in mine. I should probably get some more
screws, when I get everything put back together.
>and two clips on the front edge.
I see them. The plastic has to deform a log way before it'll release, but
I'll try it tonight.
>Next you'll need to remove the graphics board,
Yeah, that is tricky. Done it a couple times during earlier testing. The
problem first appeared when I was first using the graphics board, so I
blamed it. But I think it's working OK. At least for the moment, I'm doing
all the testing with a VT320 on the MMJ console port, so I have to
connect/disconnect less stuff when taking things apart.
>Once the graphics board is out, there are 3 more phillips screws at the
>back edge of the mainboard. The plastic clips pull up to release, but with
>the bottom shell off, you can use something to push them up from the
>underside.
Ok, that's a big help. If I can get the shell off I'll try poking them out.
>Certainly make sure they are discharged before you remove them, if you
>decide to replace them after all ;)
Ok. Short through a resistor for a minute or two? But I'm thinking right
now the comparator is the first target for replace, followed by the SMD
resistors if that doesn't do it.
- Mark
>From: ard(a)p850ug1.demon.co.uk (Tony Duell)
>I rarely bet except on certainties :-)
Yeah, me too. As you probably noted...
>>> Now *I'll* bet - Tony wants to know what the comparator *inputs* are
>>> connected to.
...
>>
>>I don;t think it's for overvoltage protection. I think this is where the
>>PowerOK signal comes from. And it's triggering at the wrong time. So
>>either the comparator is defective or there's a problem with the passive
>>components areund it, or there's a PSU fault.
>>
>>How hard is it to reverse-engineer the schematic of the components around
>>this comparator? Can't be _that_ complicated...
Yup. a sure bet. :-)
Complicated, probably not. Hard, yes. They are all surface-mount and near
microscopic. For which reason, all numbers and letters quoted below may be
wrong. Here's what I think I found:
Comparator INV Input B and Input B connect to ground (zero Ohms to chassis).
Comparator INV Input A connects to the middle pin (which points left)
of a 3-pin device marked "88W". I couldn't find that the upper right
pin connected to anything. The lower right pin connected to ground.
That input stayed very steady at about 3.4 V.
Comparator Input A connects to an orange device marked "6192" and a black
device
marked "1152". Both are 2-terminal surface-mount rectangles.
The other end of the 6192 connects to ground.
The other end of the 1152 connects to +5 (Red wire).
That input *varies substantially and irregularly*
It's at 4.2V and reasonably steady when the computer is running.
It's at 2.9V, or wavering in between when the computer is hung.
There may be *lots* of connections I missed.
"Wavering" is what I see my needle do - for all I know, the voltage may be
popping rapidly between the two values, with varying duty cycle.
Here's what I think may be happening: 6192 and 1152 are voltage-dividing
the +5V supply down to some intermediate value for the comparator. But
either the resistors are flaky (do resistors *do* that?) or the comparator
is intermittently drawing current, and throwing off the voltage-divider.
Good so far? Any way to test those theories with my analog VOM? Should I
order a new LM193 comparator chip instead of a pile of capacitors for my
first soldering attempt on this machine?
If I *do* need to pull the comparator, I'll need to take the mainboard out
of the chassis. That'll mean removing 4 extremely nasty plastic rivet
things. How do those suckers come out in such a way as to leave them
intact? I wrestled with one for a while and got nowhere.
>It can't do any harm provided the new capacitors are good, and you get
>them the right way round (they are, of course, polarised.)
I didn't make it to the electronics shop today - Kids' soccer game and
wife's Newtonsday (sic?) shopping interfered. She promised to go for me
Monday if I wanted. I explained to her what a "capacitor" is so that she
could breeze in, look knowledgeable, and say "I'd like replacements for all
the electrolytic capacitors on this board." She practiced it three or four
times so she wouldn't stumble over "electrolytic capacitors". I also
pointed at them, just for good measure.
All that notwithstanding, the capacitors may get due process after all.
- Mark
Yesterday I went by the scrapyard, and found an HP 9825B, 9825T, and 3 HP
86s... Asked what they wanted for them, and they told me "oh we wouldn't
charge you for those"... WOOHOO! But I need case parts and manuals and
keycaps, plus none of them have interface cards in them.. But the 9825T,
which is all I have powered up so far, WORKS!
Will J
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All,
Just catching up on the digest. I think next time I beg for advice I'll
take digest mode *off* first. The delay is frustrating. Tony was way ahead
of me last night, but I didn't get the benefit of his advice until this
morning.
Tony D. said:
>I will bet that
>Red = +5V
>Black = Gnd
>Orange = +12V
>Blue = -12V...
You'd win, as far as I can tell with my meter, with the minor variations
I've noted.
>> Blue is one wire, and goes to appx. 12 V. when the system is on.
>
>I would think the last one is actually -12V ?
Correct, typo on my part.
>More intersting would be to
>use a 'scope to look for noise (particularly spikes at the PSU switching
>frequency). Such spikes can make a supply rail look to be too high on
>some meters.
Yeah. Sigh. What's a likely frequency for the PSU switching? Is my
(primitive analog) VOM likely to yield any useful info if I set it to the
"AC Voltage" ranges?
>> M9124
>> LM393N
>> QST
>
>Aha. A dual voltage comparator. This could be used to check if power is
>OK, and to generate the reset signal as appropriate.
I don't know the causality yet (failure causes comparator to switch, or
comparator switching causes failure), but the comparator (at least output
A) does switch when the failure appears. Output A is Pin 1 as you recalled
and Output B Pin 7, thanks to Toth for the link to the data sheet.
Now *I'll* bet - Tony wants to know what the comparator *inputs* are
connected to. Tonight's work is cut out for me. But in any case, I'm still
guessing the power supply is a likely culprit. It looks like the comparator
is properly protecting the mainboard from an overvoltage on +5V or +3.3V. I
don't know what's going on with +3.3 being referred to something other than
ground. In either case, a lower +5V supply (= appropriate repair to the
PSU) would solve the problem.
Is replacing all of the PSU output electrolytic capacitors just on
suspicion a good move? That's what I plan for the weekend. (Lucky for me
capacitors are not entitled to due process.. :-) )
- Mark
Of possible interest to the List...
------------ Tear along dotted line ----------------------
From: jones(a)pyrite.cs.uiowa.edu (Douglas W. Jones)
Newsgroups: alt.folklore.computers
Subject: Re: ASCII control codes
Date: 31 Aug 1995 19:37:58 GMT
From article <4239uk$ko1(a)metro.ucc.su.OZ.AU>,
by adrianw@cassius (Adrian Whichello):
> Some are obviously still used for their original purpose (CR, LF, the
> tabbing codes etc.) but what did ENQ, EM, SUB, FS, etc. do? Thanks,
- - - here's a reply I posted a year ago in June - - -
Subject: Re: original uses of ASCII control codes
Newsgroups: alt.folklore.computers
References: <1994Jun02.064649.131411(a)ua1ix.ua.edu>
To understand the original intent of the ASCII control codes, you have
to think of teletypes, using paper tape, configured in a multidrop
system with relay logic used to turn on or off individual teletypes in
the bunch, and you have to remember that the designers were pretty
smart and they anticipated future developments, but they also managed
to include provisions for things that never happened. Here are the
ASCII control characters, and a few others, with comments on how they
were supposed to be used and how this relates to current popular uses:
NAME HEX/CTL USE
NULL 00 ^@ always ignored -- leader and trailer on paper tape
systems was typically made of sequences of NULLs.
SOH 01 ^A start of heading -- imagine a heading containing, for
example, the address of the recipient. You could have
relay logic that scans for SOH, then enables the print
mechanism if the following character matches this
station's address. In early documentation, this was
called start of message.
STX 02 ^B start of text -- if the heading matched, start printing
with the following character. In early documentation,
this was called end of address.
ETX 03 ^C end of text -- now is a good time to stop printing.
Your message might continue after this with a checksum
or other administrative stuff. In early documentation,
this was called end of message. The common use of
control C as a kill character stems from this -- it
indicates the end of your text addressed to some
application.
EOT 04 ^D end of transmission -- relay logic could decode this
and, if there is a tape in the tape reader, it could
begin transmitting its own message.
ENQ 05 ^E enquire -- on receiving this, local relay logic would
generate a response. In early documentation, this was
called WRU or who are you. Teletypes had programmable
response sequences that were encoded on a music box
mechanism, and it was up to the customer to break
plastic fingers off the drum to code how it responded
to an ENQ.
ACK 06 ^F acknowledge -- one possible response to ENQ. In early
documentation, this was called RU or are you.
BEL 07 ^G bell -- ring the bell in the terminal. Teletypes had
real bells where most modern terminals have beepers of
some kind. A sequence of BEL characters sent to a
teletype sounded very much like a telephone ringing.
BS 08 ^H backspace.
HT 09 ^I horizontal tab.
LF 0A ^J linefeed.
VT 0B ^K vertical tab.
FF 0C ^L formfeed -- page eject.
CR 0D ^M carrage return -- on many mechanical devices, CR was
slow. The sequence CR LF was always sent in that order
so that the linefeed could be handled while the carriage
was returning; a well adjusted Teletype could just finish
the CR in this time (0.2 seconds), and a common sign that
it was time to call the service man was that the first
letter printed after a CR LF was printed "on the fly" on
the way back to the margin.
SO 0E ^N shift out -- if you've got a two-color ribbon, shift to
the alternate color, usually red. There are obvious
extensions of this to alternate character sets.
SI 0F ^O shift in -- undo whatever SO does. For mysterious reasons
that have no apparent connection to old or modern ASCII
standards, DEC liked to use control O as a break character
to suppress teletype output.
DLE 10 ^P data link escape -- an escape character is generally a
prefix for something else. DLE was expected to be used
as a prefix on characters in the user data stream that
might otherwise be interpreted as data link control
characters, for example, flow control characters. In
some early documentation, this was called DC0 or device
control zero.
DC1 11 ^Q device control 1 -- turn on the paper tape reader.
In early documentation, this was called XON.
DC2 12 ^R device control 2 -- turn on the paper tape punch.
DC3 13 ^S device control 3 -- turn off the paper tape reader.
In early documentation, this was called XOFF, The use
of XON/XOFF (DC1/DC3) for flow control stems from their
use to control the flow of data from the paper tape
reader attached to a Teletype.
DC4 14 ^T device control 4 -- turn off the paper tape punch.
NAK 15 ^U negative acknowledge -- another possible response to ENQ.
One flow control mechanism is to use ENQ to ask if the
receiver has buffer space, and require the receiver to
respond with either ACK (yes) or NAK (no). ENQ could
also be used to enquire about whether a retransmission
is required after sending a checksum. The popular use of
control U to delete the current input line is only vaguely
grounded in this definition.
SYN 16 ^V synchronous idle -- if you're using a synchronous
transmission protocol, and you have no data to send, you
send SYN characters to keep the clocks synchronized.
The receiver should ignore these, and the transmitter may
have to insert them into the data stream once in a while.
ETB 17 ^W end of transmission block -- used when a transmission must
be broken into many blocks for some reason, for example,
to place a checksum after each block. Early documentation
called this logical end of media.
CAN 18 ^X cancel -- take that back, what I just sent you is a
mistake, ignore it.
EM 19 ^Y end of medium -- there's nothing left on this reel of
(paper) tape.
SUB 1A ^Z substitute -- the next character is from an alternate
character set. SUB X might be equivalent to SO X SI,
or it might be an alternate mechanism for extending the
character set. The common use of control Z as an end
of file character has no obvious relation to the standard.
ESC 1B ^[ escape -- the next character is to be interpreted as
something other than text, for example, it might be an
extended control character of some kind.
FS 1C ^\ file separator -- useful if you have multiple logical
files in one transmission.
GS 1D ^] group separator -- useful if files are made of groups
of records.
RS 1E ^^ record separator -- COBOL anyone?
US 1F ^_ unit separator -- are records made of units?
ALT 7D } Some early teletypes had an ALT MODE key that generated
this code instead of ESC. This was interpreted as an
escape code, which was no problem when nobody had lower
case printers, but with the advent of full 96 character
ASCII, there were obvious compatability problems.
PRE 7E ~ A few terminals had a PREFIX key that generated this code
instead of ALT MODE, with all the same problems.
DEL 7F delete -- remember, paper tape uses a hole to record each
one and no hole to record each zero. DEL is all holes,
so it can be punched over any other character to rub it
out (on old teletypes, it was the RUB or RUB OUT key).
If you mispunch a character, just back up the tape and
overpunch it with a DEL. Software is expected to ignore
DEL the same way it ignores NULL.
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Sort of off topic, but sort of not.
My department is planning to have a roast of the former director and
because he was a big user of our former VAX systems, some people think
that mounting a disk platter would be a nice touch.
Anyone have have an extra RA81/RA82 disk platter for free/cheap?
Brian Wheeler
bdwheele(a)indiana.edu
A gentlement named Ed Crawson in Texas has a TI 99/4a available for sale.
It is boxed and includes a TI data recorder, which is relatively
uncommon. He is missing the manuals but is currently searching for them.
According to the seller it is in like new condition, having been used
only slightly. He also has the TI data recorder, which is fairly
uncommon.
He wants to sell it. I told him $35 + shipping for the whole lot would be
about fair, but you can negotiate with him.
His name is Ed and he can be reached at 210/655.6400.
--
Sellam Ismail Vintage Computer Festival
------------------------------------------------------------------------------
International Man of Intrigue and Danger http://www.vintage.org
* Old computing resources for business and academia at www.VintageTech.com *
This has come up before but I can't remember it being resolved.
I often see suggestions for rejuvenating failed or dying laptop batteries using
a hi-amp source to flash them and break down the built-up crystals.
Most mention breaking the pack apart before doing this individually on each
cell. Is this because each cell might have different resistances ? Most of my
LT batteries no longer work anyway so it would be no big loss if it totalled
them. Sending a dozen or so batteries into a rebuild place is a costeffective
non-option and replacing the individual cells would still be costly.
Lawrence
lgwalker(a)mts.net
bigwalk_ca(a)yahoo.com
