G8MNY TECH 24.08.19 06:23l 94 Lines 4577 Bytes #365 (0) @ WW
BID : 18749_GB7CIP
Subj: Mixer Eurorack1804X/ItMix PM184X
Path: OK0NBR IR2UBX IW2OHX UA6ADV CX2SA N3HYM GB7CIP
Sent: 190824/0914Z @:GB7CIP.#32.GBR.EURO #:18749 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW

By G8MNY (Update Oct 18)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

I have worked on both of these Behringer 10ch AF Mixers, "T Mix PM184X" has a plastic carrying handle & a huge 375W/ch (4Ω) 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
┌─────────────────────────────┐
XLR│O O O O O O . . o o o o │ 6 XLR Mic/mono Jack line +4 tone controls Jack│o o o o o o · · o o o o │
LF│· · · · · · o o o o o o │ 4 Stereo 2 Jack ins +4 tone controls Gain│∙ ∙ ∙ ∙ ∙ ∙ o o o o o'o'o │
│=============================│ 1 Aux Jack & 1 Phono Tape In & Out
Top2│∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ │
Top1│∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ █████ ▐▐ │B 32 mode FX echo 24bit processor
Mid│∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ █FX██ ▐▐ │a
Bas│∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ █████ ▐▐ │r Aux & Separate Alt/Solo Mix functions
Aux│∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ │
│ · · · · · · · · · ·||EQ|| ' │ 7 Band Graphic EQ.
Fx│∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ · · │
Pan│∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ ∙ :∙ · │ All Ch have ext rear Jack effect option
│: : : : : : : : : : . . . . │
│| | | | | | | | | | | | | ||│ XLR Bal & Jack Un O/Ps

│| | | | | | | | | | | | | ||│
│| | | | | | | | | | | | | ||│Main
└─────────────────────────────┘L&R
Faders Aux Fx Alt

The 1st Mixer+Amp was not working properly, it had a broken LS screw post, & a very noisy mixer. On painstakingly opening it up, literally 100s of knobs jacks nuts & screws, (1 needed drilling out) to release 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 £20, 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 did not want to wreck the now "good mixer" for spares, so I went back to the PM184X Mixer+Amp again (found I kept all the parts). Removing the duff SM IC I had previously found, but the loud crackle noise was still there! I also spotted the overload/PFL LEDs would not light. Testing it further, on its own PSU in the PA compartment, I found a symular 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 2A fuse wire. Re-testing all 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, & 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. Then do a good test out. A very hot 2x 4R large dummy load with the 375W/Ch amp. :=)

It has now been used at a function quite reliably, (spare taken too in case) so eventually it was well worth all that hassle in the end.


Why Don't U send an interesting bul?


--- Mystic BBS v1.12 A43 (Linux/32)
* Origin: HAMRADIO telnet slacko.kozow.com (21:5/101)