Hi. Stabilant 22 was touted highly by Jerry Pournelle in Byte magazine
as a contact enhancer, it might help after a good de-gunking.
http://www.stabilant.com/
http://www.byte.com/art/9705/sec13/art1.htm
"Stabilant 22, the miracle all-purpose contact enhancer. It not only makes
for better electrical contacts -- a major use of Stabilant 22 is to get all
the electrical noise out of hi-fi systems -- but also lubricates connector
insertions. If you don't use Stabilant 22, I bet you wish you did."
At 05:23 PM 2/7/00 -0500, you wrote:
>Two weeks ago I *had* restored it.... and about every half hour it would
>break down with a different problem. I am posting this message in the hope
>that if anyone else ever has to restore such a nasty transistor mini then
>they can use this as a reference for *everything* that can go wrong with a
>minicomputer (excluding the power supply).
>
>First, the best methods I have found to eliminate the main problems in the
>most stubborn transistor minicomputers:
>
>1) Bad contacts on backplane - Spray it with "Engine Gunk" (seriously, an
>automotive engine degreaser/cleaner), then stick a plain extender board with
>cloth wrapped around contacts and insert/remove a couple of times. Then use
>contact cleaner.
>
>2) Weak Transistors - Lower the power supply voltage enough that poor
>transistors start to fail.
>
>3) Thermal Transistor Breakdowns - (these are the Fairchild transistors that
>*always* fail due to the epoxy inside expanding and breaking contact). I
>recommend leaving the minicomputer on for 5 hours and let the poor
>transistors completely fail. Nothing worse than an intermittent one. BTW, I
>had 18 Flip Chips filled with this problem :-( (thanks for the info
>Allison!)
>
>4) Intermittent Flip Chips - These occur in areas where the mini is running
>hot (ie: The MB register) and cause poor solder contacts which *might* be
>visible. I recommend pulling these altogether and replacing them. 100s of
>ticking timebombs. Get rid of all of them before you go insane. Use a
>digital thermometer and check for areas in excess of 115 degrees F (35 C).
>In the last 3 transistor minicomputers I have restored over the past 5
>months I have found you will get a lot more intermittents if the mini was
>used *a lot* (ie: 12 years) and was stored in an area that varied greatly in
>temperature.
>
>5) Expect your prints not to contain a complete schematic of the mini
>computer - I have found many changes to the straight-8, PDP-8/S that were
>not listed in FCOs but instead new prints were issued. (1960's)
>
>COMMON PDP-8/S Problems I have found:
>
>Since the speed at which data is switched through the PDP-8/S is *much*
>faster than the Straight-8 expect problems and replace/resolder the major
>registers and *ALL* pulse amplifiers. Most pulse amplifiers are switching at
>the maximum speed for such a Flip Chip (R602,603) so the slightest addition
>of resistance caused by a poor solder contact will cause endless problems.
>
>
>This PDP-8/S had the following problems (beyond the ones I mentioned before)
>
>Saul Dinman decided to add a *new* interrupt called "LPC", Low Power
>Condition. It will look like a negibus device interrupting the CPU but in
>fact is a few gates wired to the power monitor board. Of course, it only
>affects *PARTS* :-( of the CPU like... Parity! ,ION, and other nasty *bugs*.
>As the original 8/S did not have this installed it was not included in
>original prints :-(. I now found a third set with these mods... after
>spending a couple of hours pulling my hair out. After polling for interrupts
>and a memory parity error it is safe to conclude it is a low poer condition.
>Thanks Saul!
>
>
>Of course, everything else *only* failed when the CPU was running a
>program..
>
> It's OLD instruction set was:
>=========================================
>
>ION when an external device draws *just* enough power when being accessed to
>cause an LPC rather than an IO Interrupt :-(.
>
>Clear Accumulator Sometimes - (external device control) when warm and only
>when running a program and oscilloscope is not connected.
>
>Move AC->MB , 99 out of 100 times asked to.
>
>Stall CPU Clock 1mS - no longer or it might be seen without scope.
>
>and my favorite...
>
>If Zero, Branch Sometimes - BUT branch always in SI mode.
>
>=========================================================================
>
>The PDP-8/S has now been running for over 6 hours and every major "bit"
>junction has been checked for a poor signal - all Fairchild's removed and
>buried. The desktop 8/S is a micro-sauna which means I will probably install
>fast boxer fans in place of the two eggbeaters currently installed in the
>back. My rackmount 8/s has 4 fans along the sides of the boards + 2 blowers,
>one above and one below.
>
>
>I am installing a 20ma->RS232 converter and will get this mini connected to
>Telnet with FOCAL loaded as quickly as I can. This mini needs a good month
>of continuous running to make sure it is finally... happy.
>
>PAPER TAPE: If anyone here is using a PC0 with a PC01 controller
>(Straight-8, or 8/S) I found internal mods used at DEC to increase the read
>speed from 300CPS to 650CPS... error free! 8/S *really* loads FOCAL fast
>now!
>
>
>I hope when I get a KA10 it isn't filled with the nasty problems this one
>had.
>
>
>
>john
>
>
>
>PDP-8 and other rare mini computers
>
>http://www.pdp8.com
>
>
>
>
Received on Mon Feb 07 2000 - 19:47:02 GMT