[sebhc] H89 strange problems....

[Dwight Elvey]

>From: "Lee Hart" <leeahart at earthlink.net>
---snip---
>Very close! Robin, open the case and look at P101, the white 8-pin connector 
>at the rearmost edge of the little power supply board, directly under the 
>fan. You will see two yellow wires. I'll bet you this connector is getting 
>hot and discolored around those yellow wires. The connection is going bad, 
>adding resistance and voltage drop, so the 5v regulator is not working 
>properly.
>
---snip---

Hi
 If the connectors haven't degraded too much, there is
another solution that I've been using for years on high
current connectors.
 I put silicon grease on the pins. ( note: This is NOT
heat sink grease ). Several of the products I've used
are DC#4 ( DowCorning ), Silglyde ( from automotive
shop ), and A grease sold by Napa automotive shops.
 Every time I've suggested this, many seem to come up
with all kinds of reasons not to use it. In most cases,
they are wrong but what can I say.
 While at Intel we did studies of this, including and
environmental test. It came through with flying colors
except for one problem. If any of the grease got on
components that were to be later marked, the stamped
marks would not stay on the parts.
 Electrically, it works wonders. As an example, on edge
connectors, we typically saw a 10 to 15 milliohms on
a gold to gold contact. You say, not to bad. But when
we added the grease to the connectors, it dropped to
around 1 to 2 milliohms ( the limits of our measuring
tools ).
Things that others have stated as objections:
1. When it gets hot it will run on other electrical parts
 and cause problems.
 Answer: First it is electrically in active and it is
  one of the few substances that get thicker with temperature.
2. It well get into switches and cause failures.
 Answer: I actually put it in switches to improve there
  operation, both low current and high current. In high
  current, it helps to eliminate arcing. In low current,
  it reduces the need to have scrubbing to remove oxides
  and reduces resistance.
3. It is messy to use.
 Answer: Yes, but it does work.
 
Places that I've seen it not work well:
1. very high impedance analog circuits. This is in electrometers
 and I only saw issues with the automotive products and not
 with DC#4. These problems only showed with resistances in
 the order of 10^9 ohms and greater. I suspect that is a
 difference in the purity of the products.
  I've not seen any issues over time using the other greases
 in logic and other circuits.
2. Places that are exposed to strong salt air. In these
 case, we are talking about boat applications. There are
 a few other products that are listed for this application.
 Still, talking to a fellow that works with undersea measurement
 systems, they use DC#4 in things like BNC connectors
 to keep the water from entering the connectors from pressure.
 
Places it does work well:
1. Battery connectors
2. The RAM packs connected to the back of the ZX81's. Anyone
 that has played with the expanded RAM modules on the Sinclair's
 knows what this is about. After applying grease, one could
 bounce the computer w/ RAM on the table without losing
 any data in the RAM ( a remarkable demonstration ).
3. Various EPROM sockets. Although replacing them with
 machine pin sockets is best, the grease will often get
 things working. It won't solve broken internal pins of
 the socket, as often happens because of the way the pins
 were manufactured.
4. High current connectors. This includes most any micro
 processor connectors as well as some truly high current
 applications. By high current, I mean 500 to 1000 amps.
5. Slide switches that have suffered some from water based
 fluxes.
6. TV turret tuner contacts.
7. High current switches that suffer from arcing.

Dwight


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