Re: Restoring rubber keyboard on a logic analyzer

[Chuck Guzis via cctalk]

Answered my own question.  The repair stuff is called "Aquadag E":

https://semicro.org/products/carbon-paint-conductive

https://www.ebay.com/itm/AQUADAG-CARBON-PAINT-ARCADE-MONITOR-TV-CRT-CATHODE-REPAIR-SPARES-30-ML-BRUSH-/261808496366

Should work a treat in this application.

--Chuck

Re: Restoring rubber keyboard on a logic analyzer

[Chuck Guzis via cctalk]

On 04/29/2018 08:44 PM, Tony Duell via cctalk wrote:

> It's not cheap (and IIRC you have to use the whole lot in one go), but
> Chemtronics make a kit to repair such keypads. Possibly worth it for
> a useful instrument though.
> 
> In the UK you can get it here :
> 
> https://uk.rs-online.com/web/p/conductive-adhesives/3888673/
> 
> and I guess it's also available across the Pond.

Does anyone still make aquadag?

--Chuck

Re: Restoring rubber keyboard on a logic analyzer

[Fred Cisin via cctalk]

On Mon, 30 Apr 2018, Tony Duell via cctalk wrote:

In the UK you can get it here :
https://uk.rs-online.com/web/p/conductive-adhesives/3888673/
and I guess it's also available across the Pond.


Silly thought:
Half a century ago, there used to be a conductive glue that was peddled 
to the general [not even owning a soldering iron] public as heat-less 
solder.


If that's still available in any form, would that work?


There is some stuff that claims to be a conductive paint:
https://www.amazon.com/Bare-Conductive-BarePaint-Paint/dp/B076BSBMK6

Re: Restoring rubber keyboard on a logic analyzer

[Tony Duell via cctalk]

On Sun, Apr 29, 2018 at 11:29 PM, Maciej W. Rozycki via cctalk
 wrote:
> On Sun, 29 Apr 2018, Paul Koning via cctalk wrote:
>
>> So that's the answer: graphite powder.  I now have a working analyzer
>> again.  It will be interesting to see if the graphite wears off
>> eventually, I suppose it might but that's ok, I can just do it again.
>
>  Many years ago I used graphite obtained from a soft pencil to revive
> rubber keyboard pads and from my observation it wore rather quickly, in
> particular moving to the surface contact was made against.  I wonder if
> there is a non-industrial way to make graphite stay in place on rubber.

It's not cheap (and IIRC you have to use the whole lot in one go), but
Chemtronics make a kit to repair such keypads. Possibly worth it for
a useful instrument though.

In the UK you can get it here :

https://uk.rs-online.com/web/p/conductive-adhesives/3888673/

and I guess it's also available across the Pond.

-tony



>
>   Maciej

Re: Restoring rubber keyboard on a logic analyzer

[Maciej W. Rozycki via cctalk]

On Sun, 29 Apr 2018, Paul Koning via cctalk wrote:

> So that's the answer: graphite powder.  I now have a working analyzer 
> again.  It will be interesting to see if the graphite wears off 
> eventually, I suppose it might but that's ok, I can just do it again.

 Many years ago I used graphite obtained from a soft pencil to revive 
rubber keyboard pads and from my observation it wore rather quickly, in 
particular moving to the surface contact was made against.  I wonder if 
there is a non-industrial way to make graphite stay in place on rubber.

  Maciej

Re: Identifying bad RAM on Amiga 1000 WCS board

[Ethan Dicks via cctalk]

On Sun, Apr 29, 2018 at 12:25 PM, Richard Sheppard via cctalk
 wrote:
>> There are hand-drawn schematics floating around but they don't appear
>> to match the production hardware
>
> There is a service manual - "Amiga Computer Model 1000 Preliminary Component 
> Level Repair PN 314038-02" which does show those PALs on page 1-25 "Amiga 
> piggyback PCB assy #327139"

Examining that carefully, I do see the WCS parts entwined with the
mainboard parts on the schematic at the back of the guide.  The copy
of the scan I have (from archive.org) does not show a Page 1-25.
Chapter 1 ends with the keyboards tests on 1-16.

I was more referring to a couple of standalone pages with what looks
like a different rev of the WCS board.  The DRAM chips and associated
resistors and, well, most of the parts have different location/ID
codes.  Googling for "Amiga 327139", I found a reference with the
following info:

A1000 piggyback board327139
A1000 piggyback board   Rev A327106-01

This is likely the difference.  The standalone "piggyback board"
schematics _are_ marked "Rev A" in the comment box.

I've also seen pictures of later Amiga 1000s with all the components
on the mainboard and no daughtercard, but I've never seen a machine in
person like that.

-ethan

Re: Restoring rubber keyboard on a logic analyzer

[Paul Koning via cctalk]

> On Apr 26, 2018, at 12:32 PM, Electronics Plus via cctalk 
>  wrote:
> 
> Easier solution is to apply some conductive light lube. Radio Shack used to
> carry it, and I repaired a LOT of remote controls with it!
> 
> Cindy

I made a successful repair.  Here are the steps I used:

As I mentioned, I tried cleaning with isopropyl alcohol, without much success.  

I realized that I could test the rubber contact points with a multimeter, 
probing two spots on the surface.  The offending keys had much higher 
resistance or simply tested open.  That made it easier to try other options 
without having to assemble/disassemble each time.

I found a spray can of "contact cleaner/lubricant" and tried that.  OOPS.  Made 
it much worse.  Looked at the ingredients: one is "mineral oil".  Ok, so that's 
fine for metal wiping contacts I suppose, but not for this.  Washed the keypad 
thoroughly with dishwashing soap and water, then wiped several times with 
alcohol, that got me back to where I was.

Then I realized I still have a tube of powdered graphite (the stuff sometimes 
used for lubricating locks, though it turns out that's not a good idea.  
Squirted some onto a Q-tip and rubbed the bad contact pads with that.  They 
look shiny as a result rather than dull black.  But it works!

So that's the answer: graphite powder.  I now have a working analyzer again.  
It will be interesting to see if the graphite wears off eventually, I suppose 
it might but that's ok, I can just do it again.

Thanks everyone for the suggestions.

paul

Re: Identifying bad RAM on Amiga 1000 WCS board

[Richard Sheppard via cctalk]

> There are hand-drawn schematics floating around but they don't appear
> to match the production hardware

There is a service manual - "Amiga Computer Model 1000 Preliminary Component 
Level Repair PN 314038-02" which does show those PALs on page 1-25 "Amiga 
piggyback PCB assy #327139"

Richard Sheppard

Identifying bad RAM on Amiga 1000 WCS board

[Ethan Dicks via cctalk]

Hi, All,

I've been doing component-level diagnosis of a bad Amiga 1000 WCS
board and since I was unable to find this information anywhere, I
thought I'd post it to the list so that it's in the hands of more than
one person.

For an Amiga 1000 that starts up with a turquoise screen and never
asks for Kickstart, it means that the WCS RAM test has failed.  Common
causes are one or more bad 4464 DRAM chips on the WCS board or a bad
PAL.  I don't happen to have the PAL equations but I did spend some
time with a sick Amiga 1000, a Fluke 9010A and a cheap digital scope.

There are hand-drawn schematics floating around but they don't appear
to match the production hardware in either part placement or
completeness (the schematics describe 2 PALs, DAUGCAS and DAUGEN, but
the production hardware has two additional PALs, DPALCAS and DPALEN,
for one specific example).

If one has a Fluke 9010A and 68000 pod, one can test the WCS RAM by
pressing [RUN UUT] and turning on the Amiga and waiting a second or
two for the ROMs to set the right memory map bits to make the WCS
writable.  One can then do simple [READ] and [WRITE] tests to the
Amiga at $FC-$FF and even run a [RAM SHORT] on part or all of
that range (a RAM SHORT test on 256Kbytes will take more than a few
minutes).

The memory itself is a bank of 8 4464/50464 64Kx4 DRAMs at U1B-U1E and
U2B-U2E, arranged sensibly in two banks of 128Kbytes.  The chips in
row 2 are the lower half ($FC-$FD) and the chips in row 1 are
the upper half ($FE-$FF).  The individual bits are arranged as
follows:

U1E/U2E $000F D0-D3
U1D/U2D $00F0 D4-D7
U1C/U2C $0F00 D8-D11
U1B/U2B $F000 D12-D15

For those that want to trace individual bits the order on each DRAM is
pin-3, pin-2, pin-15, pin-17 which is slightly off the given order on
the 4464 datasheet of 2,3,15,17.

By way of verification, the WCS board I'm repairing failed the RAM
test with bad bits at $F000 when I pulled the defective chip from
position U1B.  The same chip failed testing in a Ming HT-21 "Handy
Tester" DIP logic and DRAM tester (but passed when tested as a 4416,
because the fault was not in the first 25% of the memory cells).

-ethan