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G8MNY > TECH 02.01.22 11:00l 93 Lines 4654 Bytes #999 (0) @ WW
BID : 57235_GB7CIP
Read: GUEST
Subj: Mixer Eurorack1804X/ItMix PM184X
Path: IW8PGT<LU4ECL<GB7CIP
Sent: 220102/0857Z @:GB7CIP.#32.GBR.EURO #:57235 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Update Jan 20)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
I have worked on both of these Behringer type 10ch AF Mixers, "T Mix PM184X"
has a plastic carrying handle & a huge 375W/ch (4ê) PA amp built in underneath.
The "Eurotrack 1804X" is a mixer only & separate mains transformer.
ch 1 2 3 4 5 6 7 8 9 10 o/p
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
XLR³O O O O O O . . o o o o ³ 6 XLR Mic/mono Jack line +4 tone controls
Jack³o o o o o o ú ú o o o o ³
LF³ú ú ú ú ú ú o o o o o o ³ 4 Stereo 2 Jack ins +4 tone controls
Gain³ù ù ù ù ù ù o o o o o'o'o ³
³=============================³ 1 Aux Jack & 1 Phono Tape In & Out
Top2³ù ù ù ù ù ù ù ù ù ù ³
Top1³ù ù ù ù ù ù ù ù ù ù ÛÛÛÛÛ ÞÞ ³B 32 mode FX echo 24bit processor
Mid³ù ù ù ù ù ù ù ù ù ù ÛFXÛÛ ÞÞ ³a
Bas³ù ù ù ù ù ù ù ù ù ù ÛÛÛÛÛ ÞÞ ³r Aux & Separate Alt/Solo Mix functions
Aux³ù ù ù ù ù ù ù ù ù ù ³
³ ú ú ú ú ú ú ú ú ú ú||EQ|| ' ³ 7 Band Graphic EQ.
Fx³ù ù ù ù ù ù ù ù ù ù ú ú ³
Pan³ù ù ù ù ù ù ù ù ù ù ù ù :ù ú ³ All Ch have ext rear Jack effect option
³: : : : : : : : : : . . . . ³
³| | | | | | | | | | | | | ||³ XLR Bal & Jack Un O/Ps
³| | | | | | | | | | | | | ||³
³| | | | | | | | | | | | | ||³Main
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙL&R
Faders Aux Fx Alt
The 1st Mixer+Amp was not working properly, it had a broken LS screw post, & a
very noisy mixer. Painstakingly opening it up, literally 100s of knobs jacks
nuts & screws, (1 needed drilling out) released the large PCB. On close
inspection, it soon became apparent that a CUP OF COFFEE had done it in.
(Always power off/remove batts if this happens to you!)
I photographed the PCB with 10Mpixel camera, to show up the many tiny corrosion
points in detail on a PC screen, to see all Surface Mount bits zoomed in to
more easily check it out.
After much tinkering I found a surface mount "SM" dual Op amp IC, with a
completely corroded away +ve pin. At this point I gave up as un-reparable for a
few years!
At a Ham rally I spotted the similar 1804X "mixer only" version, for œ20, less
its external transformer & it "just had a noisy slider", so I bought it, & made
up transformer (19-0-19V 1A) PSU box for it. The bad slider was the 1st ch Mic,
so I stripped this mixer down too (another 100 knobs & screws etc.) Unsoldered
& removed the slider, opened it up, re-tensioned the wipers & put it all back
together. Then solder suckered the PCB holes to refit. All tested out OK.
Now I decided that I did not want to wreck the now "good mixer" for spares, so
I went back to the PM184X Mixer+Amp again (found I had kept all the parts).
Removing the duff SM IC I had previously found, but the loud crackle noise was
still there! I also spotted a ch overload/PFL LEDs would not light. Testing it
further, on its own PSU in the PA compartment. I found a similar SM dual Op amp
IC with no +ve rail or to that that ch's LEDs. This failed power line, I traced
to a tiny plated through PCB track "bridge failure" under a component, as this
had the same layout as other channels, I pieced it out on the non component
side with fine 2A fuse wire. On re-testing all the noise had gone.
Now to the duff SM IC, filing it's corner off, I managed to expose enough metal
(0.2mm) to tin & solder 2A fuse wire to it. Putting it back in, a steady hand
was needed for SM ICs! Hey Presto it all worked too. (wooden cocktail stick is
ideal for unblocking oversoldered fine IC legs.)
Back to the last bit, the PA Amp's broken dual post LS high current screw post,
I made a replacement part from an old similar one & made it fit.
To stop this Mixer "coffee fault" in the future, to both mixers, I added felt
rings washers cut from "J Cloth" on each of the 79 pot shafts & glued a cloth
to the cover for the 15 sliders holes & slotted them.
Before closing up, I drilled out & re-tappped the seized screw thread in the
spot welded in collar, that I had drilled the screw head off before, & replaced
the screw for "a Proper Job". Also all the screw threads were greased up to
enable easier re-assembly & undoing next time!
Then it was just the matter of the 100s screws, nuts & washed clean the knobs,
etc. And do a good test out of everything. A very hot 2x 4R large dummy loads
with the 375W/Ch amp. :=)
It has now been used at a function quite reliably, (spare taken too with my
external Amps just in case) so eventually it was well worth all that hassle in
the end.
Why Don't U send an interesting bul?
73 de John G8MNY @ GB7CIP
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