[sdiy] troubleshooting [what should be] a simple problem...

[Rude 66]

hey merlin,

this is probably going to sound stupid, but have you tried simply
resoldering the output socket that doesn't work? i've had this problem on 2
synths, and every time it was simply the solder that had come loose because
of all the in-out patching. damn %$#@#$% plastic chassis parts! but it was
the same thing, the headphone outs stillworked..

ruud (trying to keep it simple..;-)





----- Original Message -----
From: "Merlin Zener" <merlin at merlinzener.com>
To: "Synth DIY list" <synth-diy at dropmix.xs4all.nl>
Sent: Wednesday, July 02, 2003 1:35 PM
Subject: [sdiy] troubleshooting [what should be] a simple problem...


> Hi there,
>
> I have an Ensoniq MR-rack; it's a nice unit built in 1995,
> so it's reasonably modern in design and build [lots of
> surface mount]. Everything is pretty much on the one big
> board aside from power supply and front panel [LCD, two
> rotary encoders, Vol ctrl, H/phone skt and some buttons]
> and it's built really well - quite drop proof, strong
> metal case etc.
> Only trouble is, Ensoniq is out of business now, and parts
> and comics etc will be hard if not impossible to get...
>
> I'm an ex-technician - I had a business back in the 90s,
> but for the last few years I've just been playing. I used
> to be on this list then, but I've only recently re-subscribed
> and been lurking a while.
>
> ANYWAY... <gr>
>
> So one day the outputs of the MR-rack stopped working. No
> reason, the unit hadn't been dropped or moved or anything,
> just turned off overnight and turned on again, and no sound
> from the MR. But get this: the headphone socket still has
> sound!!!
> I've been thinking this through - clearly this unit is not
> using the old
> D/A >>> opamp >>> outputs >>> H/phone amp >>> H/phone skt
> signal chain - otherwise there would be no sound at the
> headphone.
>
> I've had a bit of poke around but being a double sided board
> and lots of SM and no comic, I'm not able to ascertain much.
>
> One thing: the outputs on the back panel are balanced, so there
> are a couple of other possibilities:
> D/A >>> opamp >>> outputs
>     >>> H/phone amp >>> H/phone skt
>
> or even:
> D/A >>> VCA [from Vol ctrl] >>> opamp >>> outputs
>                             >>> H/phone amp >>> H/phone skt
>
> The other thing I was thinking of is maybe there are some
> FETs across the outputs for muting [I remember some Rane
> equipment around the same vintage had that idea] and maybe
> they've gone short or are being switched on by leaking
> voltage somehow. Not that there's any signs of moisture or
> cracks etc - the unit looks like new inside.
>
> There are a bunch of 3 legged SM devices with "CR15", "CR16"
> etc on the screenprint; they have "SD" or "5D" on them.
> The only other transistors in the general area, well the
> print is really small and hard to make out, but I think
> it's something like P10, with 59 at right angle. I'm assuming
> transistors - the screen says "Q12", "Q11" etc.
>
> Anyone got any ideas?
> A circuit or block diagram maybe?
> Or a contact or website etc for someone doing Ensoniq repairs
> and parts these days?
>
> TIA for any help... :)
>
>
> --
> Merlin Zener
> Piano, Synthesizer
> Pattaya Thailand
> http://www.merlinzener.com
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