Friday, September 09, 2011

Continued work on the Ramsa 8210. All remaining circuitry is supported on a removable frame seen here.

I pretty much only made it as far as the rectifier PCB of the power supply and the routing strip feeding the summing sections. It is here that the green wire bandit, who modified this mixer sometime in the annals of history, stepped up their game and made the prospect of undoing their work broach nightmare territory.

But before I tread those waters, let's have a look at this cute little stand-off which separates the rectifier/regulation/filtering PCB from the rest of circuitry (seen below). I'm really fond of external power supplies. Fortunately the AC portion is directly piggy-back the metering strips, so I doubt there's a lot of concern here, but still.. a bit close for comfort.

Besides, I've clearly got greater things to be concerned with.

It is at this point that I am pretty much prompted to do what I can to retrace what has been done so I can attempt to wrap my head around what exactly was trying to be achieved here. I foresee some hours of fruitless internet searches regarding published modifications, before throwing up my hands and deciphering. While the iron was hot, I went ahead and reversed this mod. I will be checking continuity between the severed legs before application of power, naturally.

It was at this point that I began questioning the logic and motivation behind all of the green wire mods (most of which involved cutting traces), see, all those green wires are just reflecting the printed circuit traces that originally tied everything together. So, I see this work as a pointless waste of time... which sort of guides my outlook a little on the rest of things.

Perhaps those reworked connections were due to an intermittent failure in functionality? This is the second punched pad I've come across. And if someone spent hours cutting traces and weaving a convoluted single color loom of wiring trying to correct THIS, I may have may work cut out for me here.


krivx said...

Thinking out load here - have you tried measuring the resistance of the original pcb tracks and comparing with that of the green wire lengths? Some of it looks pretty heavy-gauge, possibly someone wanted to allow for higher currents or correct thermal issues?

"Green wire fixes" are actually pretty common in early stages of manufacturing runs, green wire is usually used to correct pcb errors as it's harder to spot when it blends in with the board colour. Was the mixer a high-end model or from a small production run? If the s/n coincides with the introduction of that model then this may be an early revision with hand-corrected layout errors.

crochambeau said...

These are good points, thanks for reviving a little optimism. I don't recall, but I want to say I date coded some ICs to 82, which I think does put this at early in the run. I'll investigate when I get the chance, it would be nice if I can pinpoint something through the serial number, size of production run, etc if I can dig them up.

Direct comparison between trace and wire might not work out so well, as the circuit configuration has been changed with most of the wires, except that RCA plug section. Though honestly, I can see how *that* would be implemented at the factory if they were observing stress related failures caused by the connecting cables.

Again, thanks, a second opinion does help in quieting some concerns I was brewing. Cross that bridge when I come to it.