I broke a chip in my Emax II.
2004-01-31 by poeml@...
Hi all,
okay, it's time to write to the list :)
[First off, thanks for the great information I already found here.
Especially to the maintainers of the FAQ / archive. But also to many
other people, for example the hint to use some paint to determine where
the holes of a hard disk tray should go was really helpful to me
yesterday :) ]
I own an Emax II since a few days, but I already broke it. I initially
was in a lucky streak, because it had 8 Megs of Memory, and after some
experimenting I found a hard disk it would work with. (I tried a few
disks, but had no luck with the 8 Gig drives that I tried. Unfortunately
I had an old Quantum Trailblazer 500 Meg disk ("500MB TRBLS") in an old
Mac.) Bingo!
Unfortunately, after I had put everything together, I found that the
right channel of the main out was dead. I remembered that I had once
misplaced the ribbon cable connector to the board on the case bottom
(the one with the in-/output jacks). The connector had been fitted one
pin too far towards the back pane. By the way, when I switched the Emax
on, all LEDs were *blinking* so I noticed it immediately and turned it
off instantly.)
Analysis...
The connector to the I/O board is wired like this:
(you'll need a proportional font to properly view it)
pin #
NC ------- 40 01 ------- NC
CS pin23 ------- 39 02 ------- ?
? ------- 38 03 ------- GND
? ------- 37 04 ------- ?
? ------- 36 05 ------- GND
? ------- 35 06 ------- ?
? ------- 34 07 ------- GND
? ------- 33 08 ------- ?
CS pin16 ------- 32 09 ------- GND
CS pin15 ------- 31 10 ------- CS pin14
NC ------- 30 11 ------- GND
NC ------- 29 12 ------- DATA (to all 8 channels)
CLK ------- 28 13 ------- GND
LE SubB L ------- 27 14 ------- LE SubB R
LE SubB L ------- 26 15 ------- LE SubA R
GND ------- 25 16 ------- LE SubA L
LE Main R * ------- 24 17 ------- LE Main L
LS SUBC R ------- 23 18 ------- GND
-12?V ------- 22 19 ------- +5V
-12?V ------- 21 20 ------- +5V
There are 8 lines labelled "LE", one for each physical output channel
(SubA, B, C, Main, each times 2). The digital data is sent in sync with
CLK (clock) through the DATA line, which runs to all DATA pins of the 8
D/A converters. Interestingly, the line is shared by them all, so they
seem to be addressed one after the other.
The D/A converters are AD1860N and made by Analog Devices, Inc. Specs
can be found here:
<http://www.analog.com/Analog_Root/productPage/productHome/0,2121,AD1861,00.html>
(The 1861 is a compatible successor of eh 1860).
The lines labelled "LE" carry a signal ("Latch Enable") that tells the
AD1860N when transmitted 16-bit word starts, by a short impulse. (That's
when the AD1860N starts to collect 16 clocked serial bits until and
converts them to an analog value.)
In my case, the LE line for the Main R channel got grounded when I
misplaced the connector. What should in fact go to pin 24, went to pin
25 (GND), and so on...
After looking at the circuit, and fooling with a voltmeter it has become
pretty clear that the pin 24 line now carries +5V, which is _not_ what
it is supposed to do... I first hoped that it would be due to a broken
AD1860N, but with the entire I/O board disconnected it still carries
+5V, and the line comes directly out of the huge custom E-mu labelled
chip in the left hand corner of the motherboard. Too bad!
The AD1860N D/A converter never gets the Latch Enable signal, and in
fact it outputs 3 Volts of current to its output.
Thus, this chip is broken. At least partly -- the other channels seem to
work fine still, but I'd need to look further. Even the A/D convertor
could be broken, I haven't tried sampling yet. But it seems that I can
continue (or, begin ;-) using my new Emax by using the rest of the
channels...
Still, I would like to know whether anyone has parts for replacement to
share -- maybe a broken Emax II in the cellar...
I take it that these kind of chips are no longer available for
replacement from E-mu?
Lesson learnt: CHECK ALL CONNECTORS TWICE. It always happens to me, but
the Emax II is quite unprotected, you can misplace the connectors in all
directions without protection, and it doesn't like it!
Still it's interesting to learn about the internals of the Emax II. In
fact, it would seem feasible to replace it's D/A converters with newer
ones with even better specs (just a foolish idea ;-)
For reference, since I took the time to figure it out, here's a scheme
of where which of the D/A converters is sitated on the board:
|-------------------------------------------------------------------------
|Sample SubC-L SubC-R SubB-L SubB-R SubA-L SubA-R Main-L Main-R Mono Phone
|-------------------------------------------------------------------------
|
|
|
| SubA-R IC21 IC14 SubB-L
|
| x CS ES SubA-L IC21 IC14 SubB-R
| x CS ES
| x CS ES Main-R IC21 IC14 SubC-L
| x CS ES
| x Main-L IC21 IC14 SubC-R
| x
|
|
|--------------------------------------------------------------------------
As seen from the "wired" face of the board.
xxxxxx is the 40 pin connector to the mainboard.
CS is the Crystal Semiconductor 5326 ADC.
ES is an empty socket.
Peter
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