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Help ME Save This AMEK Rack & Power Supply
Old 7th February 2009
  #1
Gear Nut
 
dcharrison's Avatar
 
🎧 15 years
Help ME Save This AMEK Rack & Power Supply

I recently acquired a lovely Amek RM01 rack with 8 PM01 equalizers and 2 CL01 compressor limiters. It's 4 RU high and just perfect for my needs.

Unfortunately, somewhere en route, the power supply, a 2RU monster labeled only "PSU", took a knock stout enough to sheer off the bolt holding down the toroidal transformer, which then became the proverbial bull in the china shop.


I really don't want to queer this deal and I know the guy that sold it to me doesn't, either. It looks like all that happened was that the plastic wrap on the toroid was damaged, but I can't be certain that the windings aren't damaged. There are some spade lugs that have come loose, but I am pretty certain how they go back. I don't want to take any chances on plugging it in and doing more damage. Any ideas on proper procedure for ringing this out would be greatly appreciated.

Likewise, service manuals and docs would be most helpful. I gather from other posts that this probably ran on +/-17v rails and also had +48 for phantom, but I would like to know for sure. There appear to be three pairs of secondary wires coming off the toroid, 2 yellow wires @about 14 ga, 2 grey @about 14 ga, and 2 white @about 18 ga. The circuit board is labeled:
294
294 V-0 MCI/3/

I have put some pictures up on Google for your perusal.
Picasa Web Albums - David - Amek
Come, oh ye wise ones, enlighten this poor fool.

Last edited by dcharrison; 8th February 2009 at 10:50 AM.. Reason: Add Pix
Old 7th February 2009
  #2
Gear Nut
 
dcharrison's Avatar
 
🎧 15 years
Bump!
Old 9th February 2009 | Show parent
  #3
Lives for gear
 
🎧 15 years
Hi
If the transformer really has been 'running loose' then examine it VERY thoroughly for damaged windings. Fortunately the mains primaries are on the inside so electrical safety is unlikely to be seriously compromised.
The rack won't need phantom power for those modules so a replacement transformer with 2 windings of say 20 to 22 Volts at 5 Amps each would be sufficient. The original would have been rather more powerful but you are not trying to power a full desk.
The schematic for your unit appeared on another thread about AMEK and supplies.
Matt S
Old 11th February 2009 | Show parent
  #4
Gear Nut
 
dcharrison's Avatar
 
🎧 15 years
Thanks, and now...

Gracias. I found the power supply schematic posted earlier and also received a clean copy from one of our overseas friends. (I am in Texas).

Now I am starting to worry about resolving the connections to the terminal strips on the back of the rack. There is a 12 lug terminal strip for each of the modules and one for power. Other than some incomplete handwritten clues, there are no markings on them. The last two look like this on the outside:



...And like this on the inside


There is also one marked like this:


Anyone have access to a schematic or a working rack?
Old 14th February 2009 | Show parent
  #5
Lives for gear
 
ulysses's Avatar
 
🎧 15 years
The 94-V-0 is not the board name. That's the flammability rating of the material the board is made out of.

In photo number 19 of 21, you can see where a bunch of circuitboard traces connect to your power terminals on the end of the module backplane board. The fattest trace is the one that connects to a whole bunch of pins. That's clearly the power ground connection. The skinny trace above that only connects to one pin, and I would expect that to be your phantom power connection. I expect the 3rd and 5th traces to be your bipolar rails, with a ground trace between them. You can see that each of these two traces connects to three pins on the power terminal block.

Now you can take this theoretical idea of the power pin-out and verify it. Look at those Nubus-style connectors and figure out which pins of the modules connect to which of these two power rails. These connectors use only the A and C columns of pins, not the middle B column. For power connections, I expect the two pins in each row to be connected together.

Then look at a module and see if these in face are the pins that feed power to your audio circuitry. There will be polarized electrolytic decoupling capacitors between each power rail and ground. By observing the polarity of those capacitors, you can determine which is supposed to get positive volts and which gets negative volts. Likewise, you can easily find the very top pair of pins on the module (which I suspect are the 48V pins) and see if they are connected to a decoupling cap with a higher voltage rating (probably 63V). On the compressor modules, these pins probably don't go anywhere at all.

Figuring out the connections for the spades inside the power supply is a similar task, but it should be even easier since there are text labels next to the lugs on the PCB.

Assuming you get those spade lugs hooked up properly, I don't think the possibility of damage to the power transformer can cause any further damage to anything downstream of the transformer. Just make sure there's a properly-rated fuse installed and see what happens. The only likely transformer damage would be if the enamel is scraped off the wires and they short out. That would lower the secondary voltage, so you aren't going to hurt the power supply boards. If the primary was damaged, it could raise the secondary voltage (by increasing the turns ratio) but that doesn't look like a possibility here. So get it reconnected, give it a whirl, and if the transformer smokes then you know you already needed a new transformer.
Old 14th February 2009 | Show parent
  #6
Lives for gear
 
🎧 15 years
Hi
By reading all the above posts you should be able to sort it out from here.
Looking at the pics there are a pair of thin traces part way down the board which 'break out' in pairs between connectors. I think these will be the linling busses as they give the oportunity to 'cut' between modules and as they have holes, remake the connection if needed.
I have a diagram for a CLO1 somewhere which would help but it is quicker for you to look at the boards as Ulysses says and you can see the general state of the components while you are there.
Matt S
PS when first powering it up, only have 1 module in place so you only risk one!
Old 14th February 2009 | Show parent
  #7
Lives for gear
 
Mylithra's Avatar
 
🎧 10 years
Use the light bulb current limiter when you power up as well. (Wire a 100w light bulb in line with your mains, Ill post a picture of mine when I get home to give you the idea) If the transformer is bad or you have a winding wire to ground, the light bulb with glow really brightly and burn out but may save your transformer or the other components.

Saved my butt on a couple of builds.
Old 14th February 2009 | Show parent
  #8
Lives for gear
 
🎧 15 years
Hi
Yes the lightbulb 'trick'.
Wire up a mains bulb socket safely in series with the live of your supply cable then you can fit any size of bulb. 40 or 60 watt should be sufficient to get it at least showing signs of life.
The bulb won't burn out, just glow at normal max brightness if the transformer is 'shorted'. Normally it would glow faintly or not at all (after an initial 'flash' as the big capacitors charge and the transformer gets itself 'magnetised').
Matt S
Old 19th February 2009 | Show parent
  #9
Gear Nut
 
dcharrison's Avatar
 
🎧 15 years
TNX

As always, I am humbled by the depth of knowledge and the generosity of spirit evident in this forum. Thanks for all the good info.

I visited with my brother, the family savant, this weekend and we confirmed all the wiring in the power supply and gave it a test. Seems to be working okey-dokey-- except the fan is kaput. Our meter also showed slightly more than 17.5v, but I am currently operating under the assumption that the discrepancy is meter error or perhaps the absence of a proper load.

The rest of the detective work seems pretty straight forward. I received a schematic of the CL01 and it shows a "high level input" and a "low level input" as well as high and low level outputs. Is this -10 for low and +4 for high?
Old 19th February 2009 | Show parent
  #10
Lives for gear
 
🎧 15 years
Hi
The power rails are set using resistors not presets I think on these units.
In any case as long as it is not more than 18 Volts you don't need to do anything.
Yes dual levels were available to suit more situations.
You probably don't need the fan when only powering this small rack. These supplies were built for complete desks and so completely over rated in this application. It was easier to pull a design from production than set about making 'small' supplies involving new metalwork and so on.
A '250' supply from the much later Bullet or B2 desk would be a good alternative if it were needed.
Matt S
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