Flat Ribbon Cable Gurus??

[HarryDoPECC]

I've been struggling to get an SD-card Floppy Emulator working with my HP 54624A scope.  Using the HxC emulator on a Lotharek board (nice solution to replace old 1.44 FDDs, I have got a few working well).  The swap did not go smoothly (odd ZIF connector pinout on the TEAC FDD) and then I struck another problem, maybe the experts here can advise:

The emulator is working if I use the original HP flat ribbon - marked AWM 2896 80C VW-1.   But the original is 150mm - too short to fit the emulator into the front panel!
So order from China and get some 200mm long and marked AWM 20624 80C 60V VW-1.  Ribbon is thinner, traces are narrower but pitch is same and cable is physically compatible.

However, the emulator does not work, powers up OK but does not respond to commands from MoBo, so fails startup tests.  The emulator does work with the original cable!  I'm surprised, and Not Happy.  Got 5 ribbons for the price, all test OK for continuity and all fail to work.

I guess the longer cable could be picking up more noise, but could there be other significant differences in the cable characteristics? 

Original cable is AWN 2896 and substitute is AWM 20264.  I cannot google the meaning of these codes.  Any cable experts can advise if the cables are significantly different?  Have I got nasty fake cable or is the different coding significant?

Thanks for any info/help!

[Dave]

Check the supply rails on the emulator and compare the voltages with both cables. The thinner cable might be dropping too much voltage.

[Siwastaja]

Check the supply rails on the emulator and compare the voltages with both cables. The thinner cable might be dropping too much voltage.

And this needs to be done with an oscillosscope, trigger set just a few percents below the DC level, then used in single-shot or normal mode (not auto), so you can capture any short dip in the supply voltage.

This is because such loads tend to take short spikes. A multimeter won't reveal the voltage fluctuations.

[HarryDoPECC]

Thanks, I will do this and try to report back.

My main question was really to see if anyone can decode the cable codes - what do they mean about differences? 

It's easier to get 20624 - but do I need to chase 2896?  If I knew what these codes meant then that could help.

Thanks all, it's great how quickly people get interested and offer knowledge!

[HwAoRrDk]

AWM stands for Appliance Wiring Material, and is a system of classification used by UL to identify different styles of wire.

You can look them up:
http://iq.ul.com/awm/stylepage.aspx?Style=2896
http://iq.ul.com/awm/stylepage.aspx?Style=20624

The 20264 style for that ribbon doesn't really properly match what you have, as UL classifies that style as 2-3 core speaker wire.

Edit: whoops, made a typo when searching (20264 vs. 20624) and got the wrong thing.

[HarryDoPECC]

Thanks, that was helpful.
Those specs are physical/material/construction, nothing electrical or performance related.

Working theory at this stage is that the substitute cable is inadequate, I have found another source and I will try that before measuring and working out if it's power (I could supply separate power to the emulator) or signal - that will be harder if I cannot get a good cable.

Will try to report on the outcome.

[thermistor-guy]

...
However, the emulator does not work, powers up OK but does not respond to commands from MoBo, so fails startup tests.  The emulator does work with the original cable!  I'm surprised, and Not Happy.  Got 5 ribbons for the price, all test OK for continuity and all fail to work.
...

Are you using IDC connectors on the ribbon cable? if so, check your cable assemblies for short-circuits between adjacent conductors. Shorts can occur when the connectors are fitted, if the cable is not aligned well to the IDC tines.

[khmiller]

i'm in nearly the same snafu.  need a cable.  did you ever solve your cable problem?  where did you find correct cable?

the only difference that i can see is that 2896 is rated for 30v, 20624 is rated for 60v.  i am quite a novice at electronic circuits so i have no idea if that would be a significant difference in specs. 

 see: https://www.globalsources.com/Flat-cable/Flexible-Flat-Cables-1008761563p.htm#1008761563


any advice appreciated

[HarryDoPECC]

Aaaah, my bad, never replied to my own post.

Problem was solved - the scope ribbon has A - B configuration:  contacts on opposite sides of the ribbon.

My first replacements were A - A.  So the pinouts were reversed.  That will do it, every time!  Fortunately the scope mobo and the FDD survived.

It was difficult to find a replacement, the usual chinese suspects only did A - A.

However, I did get one and the scope has been happy with its FDD emulator ever since.

[khmiller]

A-A / A-B !!! good one!  i once spent 2 weeks troubleshooting solenoids, alternator, starter, etc on a riding lawn mower that had run out of gas while mowing.  took me that long to figure out that i had simply left the blades engaged - thereby engaging the starter safety kill-switch.  thus - no start!  all i told my wife was "Success!!! i fixed it!!!!".

thx for the update.  i'll try the 20624.  any idea of any practical ramifications of the 30v vs 60v rating?

[HarryDoPECC]

I'd say the ratings are of little importance in this application.  The FDD is +5 supply only.

Let us know if it works out.

[teevee]

Aaaah, my bad, never replied to my own post.

Problem was solved - the scope ribbon has A - B configuration:  contacts on opposite sides of the ribbon.

My first replacements were A - A.  So the pinouts were reversed.  That will do it, every time!  Fortunately the scope mobo and the FDD survived.

It was difficult to find a replacement, the usual chinese suspects only did A - A.

However, I did get one and the scope has been happy with its FDD emulator ever since.

Just to summarize this topic, AWN 20264 is substitute to AWM 2896, correct?

[HarryDoPECC]

Based on what we learned above, I'd say 20624 can replace 2896.