EZ1073-PRE Newbild - smoked resistor with a side of silent no-sound

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LouD

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Hey guys,
Long time lurker here and I think this is my first post, so in case an intro is advised *:
ehm.. name's Lou and I started out as an intern in a big studio in the 90s, and 30 years later I'm still making coffee for clients. Only now they're my own clients. I'm currently building my second project studio, because I want to get in on the hyper lucrative recording studio business I hear about! Or I suppose I just love making stuff, using my tools, creating, you know.

Thus, having built my own 51X rack and floorbox which have served me well for many years, I figured that my new "electronics guru" status was more than up to the task of finally putting together some DIY 500 series modules (including the Eisen DIY500 that I bought like what, 13 years ago?).
Right.. well, I've been duly humbled. Not that I consider myself remotely qualified to be posting on this forum, but ho baby I'm sure is interested!

So please forgive my ignorance and/or lack of being able to rule out even the most basic culprits before posting. Short of starting at page one of Intro to DC/AC Electronics, I'm not sure where to start with troubleshooting these things, and I've got a hell of a lot more work to do getting this studio operational. I'm not looking to circumvent hiring a tech, but rather would like to learn something as I go and perhaps be able myself to contribute around here. So hints and general direction-pointing are surely welcome (as are direct answers!). Thanks for any help!!

* TL;DR

I just finished putting together 2 AML ez1073-pres and am having a different issue on each:

Module 1, a.k.a."Smokey" - a few seconds after powering up, R21 (5.6Ω) fires up in a blaze of glory, with an unpretentious smokey finish.
I don't know how to read a schematic well enough to trace potential culprits, but even if I did, I unfortunately do not have an extender jig yet (but it's on the way!). I wondered if the wires I connected to the test points (for biasing while in the rack) could have caused it somehow, but a second 5.6Ω flared up just the same without them.


Module 2, a.k.a. "Silence" - powers up fine, but passes no signal. There is a tiny bit of noise if turned all the way up, but no micorophone sound.
I was able to calibrate the bias per the directions, but I haven't figured out yet how to measure output in dBu (my meter reads dBm, dunno how to convert that or V to dBu). Though with the methods that I have tried, the readings do not react to adjusting the gain trimmer. FWIW

And that's where I'm at.
Could anyone offer any ideas/advice/a hint?
Is there a specific protocol to use on these units for tracing voltages at certain points?
I've attached the schematic, but don't seem to be able to upload w/ sufficient resolution. So here's a link to the manual as well - page 39.
And I promise, I did USFSE to the best of my ability.

Thanks again,
and sorry for the rambling

-Lou
 

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Whoops

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I don't know how to read a schematic well enough to trace potential culprits

Hi mate, you don’t need to be an electronics expert to be able to do those projects but at least reading a schematic will be needed as it’s really easy and simple. Start on that, plenty info on the web on how to do that, there’s 5-7 different symbols and lines and that’s it
 

moamps

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Module 1, a.k.a."Smokey" - a few seconds after powering up, R21 (5.6Ω) fires up in a blaze of glory, with an unpretentious smokey finish.
I don't know how to read a schematic well enough to trace potential culprits, but even if I did, I unfortunately do not have an extender jig yet (but it's on the way!). I wondered if the wires I connected to the test points (for biasing while in the rack) could have caused it somehow, but a second 5.6Ω flared up just the same without them.

R21 is placed in series with the output stage (V stage 3+) so if it burns out it means that the output stage consumes too much power. This does not mean that anything is faulty, but only that the trimmer R58 that sets the operating point of the output transistor is set incorrectly. Maybe you did not turn the trimmer R58 fully ccw before the initial power on of the preamplifier as stated on page 38 of the manual. Check this first. If the problem persists, check the solder connections on connectors PL12 and PL13 and report back.

I would recommend that you focus your energy on making one module work for you properly. After that, you will more easily fix the other one and make it work.
 

LouD

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Jun 19, 2017
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Hi mate, you don’t need to be an electronics expert to be able to do those projects but at least reading a schematic will be needed as it’s really easy and simple. Start on that, plenty info on the web on how to do that, there’s 5-7 different symbols and lines and that’s it

I can read them well enough to trace signal path and identify components, it's what I'm looking for that I'm unsure of. As in, am I checking for 16V at the output of each component until I find a discrepancy? I troubleshoot heaters and this is partly how I do that, is it similar? Is there perhaps a troubleshooting protocol specific to these units or 500 series modules in general?

R21 is placed in series with the output stage (V stage 3+) so if it burns out it means that the output stage consumes too much power. This does not mean that anything is faulty, but only that the trimmer R58 that sets the operating point of the output transistor is set incorrectly. Maybe you did not turn the trimmer R58 fully ccw before the initial power on of the preamplifier as stated on page 38 of the manual. Check this first. If the problem persists, check the solder connections on connectors PL12 and PL13 and report back.

I would recommend that you focus your energy on making one module work for you properly. After that, you will more easily fix the other one and make it work.

Ok, I will focus on Smokey first.
Hmm.. I did adjust the trimmer R58 fully ccw before powering up. However, upon double checking, now there doesn't seem to be a fully ccw position and it will just keep turning and turning and turning. Did I doing something wrong? I believe there was a stop before, but no longer.
Re: PL12 and PL13 - I see PL12 but not PL13. Do you perhaps mean PL11 and PL12 as they're both on the output board?
I checked those connections and they were fine, but upon checking the rest of the board I found a short across C47 and C48 on the PL22 side. I resoldered them and no more short, no more frying resistor. Problem solved!

But now, when it comes to adjusting the output trim I'm checking dBm(?) across pins 2 and 5. Is this correct? My meter has only dBm mode, not dBu. I was able to adjust the reading, but it jumps from 18dBm to 32dBm with nothing in between. I left it at 18 and checked the module, but I get no sound. Just some strange noise that comes and goes depending on where I hold the mic. Very strange.

So I guess my question is, am I performing the second test correctly or is the dBm setting on my meter incorrect? Any ideas about what the mic-placement dependent noise might indicate?


Thanks so much for the input guys, much appreciated!
 

Whoops

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As in, am I checking for 16V at the output of each component until I find a discrepancy?

Neve circuits work with a single rail of +24volts,
so the + and + 16v rails of the 500 series rack will just do into a DC to DC converter at the voltage input of the module to convert from 16v to 24v

Even though it works with 24V that doesnt mean at all you will get +24v at the "output of each component"
 

moamps

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Hmm.. I did adjust the trimmer R58 fully ccw before powering up. However, upon double checking, now there doesn't seem to be a fully ccw position and it will just keep turning and turning and turning. Did I doing something wrong? I believe there was a stop before, but no longer.

There are no limit on multiturn trimmers, you will hear a quiet click sound when you are at one end.
Re: PL12 and PL13 - I see PL12 but not PL13. Do you perhaps mean PL11 and PL12 as they're both on the output board?
I checked those connections and they were fine, but upon checking the rest of the board I found a short across C47 and C48 on the PL22 side. I resoldered them and no more short, no more frying resistor. Problem solved!

Yeah, I meant Pl11. First you need to check that all the modules are powered by the correct DC voltage. The reference point is -16V, the right side of the resistor R25. In relation to this point you need to measure the DC voltages on the resistors R20, 21, 22 which should be 24V. If this is ok, try to connect some 400Hz sine signal from the converter to the preamplifier input, set the gain according the manual and measure the AC voltage at the output between pins 2 and 4 with the instrument.

+20dBu is about 7,75V so you can use DMM in voltage range for measuring.
 
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