Contact Spray is HELL
Never ever use contact-spray! or the like in low voltage
connectors/equipment Often the fat that is left after the
carrier-solvent has vaporised will function as a very good insulator,
The grease will contract all kind of vermin that will eek out a living
in your equipment and over time the problem will return ever more hefty.
You'll get addicted to the stuff
Even in HI-FI-equipment this is a last resort solution, and i would
prefer kerosine to remove the crackle from a potentiometer
Also: Some types of spray will contain solvents that can effectively
dissolve plastics!
A very good way to clean dirty contacts is your everyday pencil-eraser
and iso-propyl alcohol.
Sipke de Wal
Edward Taussig wrote:
>
> 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 Tue Feb 08 2000 - 14:21:58 GMT