[chbot] 6809 Processors

[Richard Jones]

Wallace,

EMC problems are cheapest to solve during the design phase. The solution to
your problem may depend on what precautions have already been taken in the
design. Worsening behaviour may be in the interference source or the
equipment being interfered with or both. Ideally the entire system that is
susceptible will be enclosed in a Faraday cage. Wiring that needs to extend
beyond the cage may either be filtered, or have the cage extended by the
use of screened cables to equipment that is also screened or filtered. Have
you determined how many issues you have? Is it the display or the control
system locking up?

Quit a few years back I put some op amps in my radio control gear to mix
up/down and left/right to control two surfaces on a delta wing. Everything
worked really well until I extended the aerial on the transmitter when the
whole thing went nuts. In this case the solution was to put the whole
mixing assembly in a tiny metal box with extremely short lead 1n decoupling
capacitors soldered between the case and each line coming in and out of the
box.

Note that all holes and slits in the enclosure need to be much smaller than
the wavelength you need to keep out. If the control unit is already in a
box does it have enough screws to limit the slit length, and are they all
fitted?

I wonder if you have a circuit diagram for the whole setup? Before going
too far its probably worthwhile putting a reasonable bandwidth scope and
dvm around the circuit to check that supply, reset lines etc are correct
voltage levels and are noise free. Then check all address lines for 0-5v
switching and data lines for 0, 5v and floating levels. Thankfully on a
6809 there are not too many. Take care not to let the scope probes slip and
do damage. I really hesitate to suggest it, I wonder if the EPROMS are on
their way out? Maybe time to back them up if anyone still has an EPROM
reader / writer.

Hope that helps. If all else fails we could hold the next meeting at your
place, or at least hold a special clinic meeting :-)

Richard


On Mon, Feb 3, 2014 at 8:54 AM, Charles Manning <cdhmanning at gmail.com>wrote:

> Welders and compressors are a **huge** inductive load that cause all sorts
> of phase shift etc. They can also cause huge ground currents etc. The noise
> can be induced in many ways.
>
> Fitting ferrites has to be done right, with a full understanding of what
> noise you are trying to nobble otherwise you can actually make things
> **worse**.
>
> For example, if you are trying to kill a common mode signal (which these
> often are), then all the conductors for the cable should run through the
> same ferrite. Putting them through individual ferrites does not help, and
> can make it worse.
>
> If it is differential noise, then a common-mode ferrite does nothing
> useful, but can make it worse.
>
> Although parts can get more static sensitive with age, I doubt that is
> what is happening here. More likely the increase is due to either
> observation bias or other environment changes.
>
>
> I'm guessing that to make everything worse this is a 2 layer board.
>
> Try an isolating power supply. See if that helps.
>
> Good luck. you will probably need it.
>
>
>
> On Mon, Feb 3, 2014 at 8:40 AM, Marshland Engineering <
> marshland at marshland.co.nz> wrote:
>
>>  This is one for the oldies (I may be wrong) who played with micros 30
>> years ago.
>>
>> I have a CNC mill which forms most of my income. It's old but very useful
>> and accurate. It uses a 2 x 6809 processors to do the work.
>>
>> Several years ago, the control occasionally freezed when the large
>> compressor started. I say freezes but sometimes it just displays rubbish. A
>> switch off and on restores the controls.
>>
>>
>>
>> I swapped the large single phase compressor for a 3 phase one and the
>> problem went away.
>>
>>
>>
>> Then about 18 month ago, I found that whenever I welded with a high
>> frequency start, again the display would, at times, freezes. It's gradually
>> getting worse and I'm getting worried. I loose my set-up each time it
>> freezes. I added ferrite beads to some of the interconnecting cables and
>> changed the PSU caps (someone else recommendation) but hasn't really made
>> much difference.
>>
>>
>>
>> Is it an earthing issue, or do filter caps near the processors get old,
>> or a any other component past its sell by date ?
>>
>>
>>
>> If you think you can help, I'd be happy to trade machining time for fault
>> finding time or similar.
>>
>>
>>
>> Thanks Wallace
>>
>>
>>
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>
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