Revox Evolution front panel repair (#P10F1)

Soo…the Revox thing from #P10 wasn’t done at the time, and when the missing cable arrived from China (“DB9 Male to Female Gold-plated Extension Cable Pure Copper Line RS232 9 Pin Serial Connector Wire COM Core with Double Shield” for a whopping 4.53€), it didn’t really work as expected.

I wondered: Did they do fancy things with the shielding, in order to squeeze out one more connection from this otherwise 9 pin cable? The cable might have different characteristics compared to the metal-to-metal contact of the serial connectors directly sitting on top of each other. Nope, they didn’t. It’s 9 wires including at least two for power. So there’s not much going over this connection, most of the display stuff is generated inside the display unit and it just tells the dumb base unit what to do next. Great, no transmission line worries.

The display ribbon cable was broken, likely the several tries of fitting the unit to the front plate made at least one of the wire crack. That’s not the obvious result when your change to the unit is the addition of one cable that isn’t supposed to be there, but when doing multiple tries and some known-good configurations suddenly fail and others that did not work suddenly appear working, you know it’s some shady thing with connection (or contact) issues and no real electronic/electrical problem with your design.

So, open it up, see what’s inside:

Oh fuck. That’s not regular ribbon cable with stranded wiring, that is solid aluminium strips wrapped in paper.

The only thing similar to that is this type of ribbon with solid copper wiring inside:

Problem is: a) It’s already starting to delaminate (I would need almost the entire length of that strip plus another one that’s not in much better condition), b) It’s a 9-core ribbon and I need friggen 10…

As I wasn’t successful in sourcing something similar at non-astronomical HiFi voodoo pricing, I decided to use regular ribbon cable. Thankfully, the original stuff had 5.00mm or 5.08mm spacing, so regular 2.54mm cable will do just fine, if every second wire doesn’t do stupid stuff and e.g. short out adjacent lines.

I tried my best without completely opening up the display, so this is the result when soldering in-place:

Yes, I started with the right ribbon which is also much more space-confined to solder. I checked if the slightly thicker standard ribbon cable moves correctly inside the two joints of the display unit (which it does), but I couldn’t be bothered to insert the two plastic sheets that likely prevent buckling when moving from full extension to sitting 90 degrees up. That won’t happen with the front plate mount, and inserting these would actually require a complete teardown of the unit as their placement does interfere with soldering top-down. So fuck it, I left it inside the case for future restoration, but these replacement ribbons work 100% in my application. Of course the soldering looks pretty shitty, but that’s mainly because of every second ribbon being cut a bit short, and the insulation of every soldered wire being slightly scorched from the tip that has nowhere else to go. For a customer repair, I would fully disassemble the unit to get the crease protectors back in place, which also would allow soldering the (prohibitively expensive) ribbons from the backside of the PCB, without leaving uneven cuts, split ribbon braids or crappy “but it works” soldering joints. But this is mine and I don’t see the point in spending time and money for a factory-like finish…for a unit that already has 160 replaced capacitors.

Clean it, put everything back together, insert new China cable – and it works:

Hooray! :yahoo:

Leave a Reply

Your e-mail address will not be published. Required fields are marked *