Channel strip test procedure

[Sturoc]

Would like to know how to go about testing IC based channel strip.
Basically to see if the strip is working 100% as it should and to pinpoint any failing parts that need to be replaced
I have over 24 strips to check and cannot afford sending them out or having a good tech do the work,
Right now they are pulled but can be mounted back in the console's mainframe or tested individually on a bench with an external p/s

Am good with basic parts replacement stuff per soldering but would like to go deeper and learn more.
If anyone can offer a step by step how-to, this would be most appreciated, along with any Test gear suggestions i.e a scope ?

 

[Brian Roth]

A test signal generator is the very first item you need. A DAW can be used, but having both a sine AND a square wave signal isn't always easily produced with a DAW's basic "test tone" facilities. I prefer a stand-alone generator. I've observed some very competent ProTools or Logic users having to dig around in the menus to find the tone generator and then fiddle with the on-screen controls.

A scope is an essential tool if you want to go any further than "well, that channel seems to be passing some sort of signal..."

Bri

 

[Sturoc]

A test signal generator is the very first item you need. A DAW can be used, but having both a sine AND a square wave signal isn't always easily produced with a DAW's basic "test tone" facilities. I prefer a stand-alone generator. I've observed some very competent ProTools or Logic users having to dig around in the menus to find the tone generator and then fiddle with the on-screen controls.

A scope is an essential tool if you want to go any further than "well, that channel seems to be passing some sort of signal..."

Bri

Thanks Bri for the quik reply,

Will acquire a test sign gen and keep my eyes out for a good used Scope. About 2/3rds of the channel strips passed a mic signal before i pulled them for inspection and cleaning, the remaining did not or barely. So I will have to go further in testing.
Any tips on that level of testing would be greatly appreciated.

 

[gyraf]

Do you have schematics? If so, please post it..

 

[Sturoc]

Do you have schematics? If so, please post it..

Will post in the morning .

 

[Brian Roth]

Out of curiosity, what desk are you testing? Perhaps I can offer more specific testing.

Often, just removing modules, carefully cleaning the innards and reinserting them MIGHT clear some problems. Having the frame and a working power supply is a huge bonus for you. (sidebar....you know NOT to remove or insert modules with the power on.....)

I don't have a "new" suggestion for a generator but I used (still do) use one of these antiques:



I built the kit in the mid 1980's. Purists will SCREAM...."UGH! A function generator has horrible distortion levels on the sine wave out!" OK....maybe 0.5% THD. If you want ultra low distortion, then spend 4-figures for an Audio Precision. I like the specs of the wide frequency range, ULTRA flat frequency response, and ultra fast settling time when sweeping frequencies. Perfect for me when aligning tape machines. Plus, it's compact. And it can produce a square wave....more on that later.

I am sure my comments will ignite a flame war here...lol. "OMG You need a HP model 122342715!" "No, you need a BippityBoppityBoo model WTF47965!"

Sidebar....our own John Roberts designed a test set marketed by Loft. That was years ago and I forget the model number......TS-1? Cool unit if you can find one in good condition (but alas, no square wave out).

Again showing my age....for years I used a Tektronix 2215 scope. 60 MHz bandwidth dual trace. I recall when I bought it new in the 1980's it cost $2200 ($6600 today). Plenty of bandwidth for audio (but nowadays "lame" when probing around inside high sample rate/high bit width digital stuff). The 2215 was smallish for it's time.

I now have a much smaller Rigol (model????) with a fancy color screen, yada yada. Cost $500-ish. It does the job, but with only 8 bit sampling so waveforms are "jaggedy" (newer units are 12 bit) and a slow...think it's called refresh rate...it acts like a slug when rapidly changing levels or frequency. The other day I fired up my old 2215 to see if it still worked (yes) and I realized how painfully slow the Rigol "reacted".

Folks here will scream "well, you need faster digital scope." OK....so gift me some money for a new five-figure Tek digital scope! Christmas is coming up....lol!

Square wave signal generator along with a scope lets you quickly detect dying lytic caps in a console's signal path and also do a quick check of the action of EQ on each channel. I am really simplifying things here, but I can elaborate....and I bet others will chime in!

Bri

 

[ruffrecords]

I have two scopes. A digital one for making fancy measurements and grabbing pretty pics into my PC and a proper analogue one sitting underneath it for when I want to see what is actually going on.

Cheers

Ian

 

[Brian Roth]

I have two scopes. A digital one for making fancy measurements and grabbing pretty pics into my PC and a proper analogue one sitting underneath it for when I want to see what is actually going on.

Cheers

Ian

Your analog scope is how old? Do you expect the fancy looking digital scope to last that long? <G!> I will be surprised if the Rigol lives for 5 years......but it looks really fancy dancy with the color screen and menus!

Bri

 

[Matt Syson]

I was very upset when my Tektronics 2245 died as it was very handy with the cursors and 'calculations' features and being 350 MHz very handy. I have a beaten up cheap 20MHz Hameg for the workshop. I had another analogue scipe previously too but as I travelled by plane every week or two, it simply fell apart (baggage handling).
Cheap and an expensive digital scope now but it is difficult to trust what they 'think' they are displaying. An old analogue 'tells' you you are getting it wrong because the line turns into a dot as it hits the edge of the screen. A signal generator of some form is of course essential and as said, a function generator is an economic and prefectly adequate for basic measurements.
Learning how to interpret square waves will take time.
I am mighty unimpressed that Audio Precision abandonned support for their older models but that is Americans I suppose. I want my gear to do today and tomporrow wnat I am doing NOW, I don't really need 'upgrades', but reliability and consistency.

 

[Rob Flinn]

I've been using one of these for site visits, it's especially useful on plane journeys. It's not as good as a analog scope & Sig gen, but I've never not been able to do something because of it.

https://www.owon.co.uk/product-page/hds272s-70mhz-handheld-oscilloscope-with-signal-generator

 

[Ike Zimbel]

I think we are talking about two separate paths here, testing wise:
1) Audio performance: I would argue that this is best done with the modules in the desk. It takes forever, but you would test every function on every module, and signal path to and from each i/o point (Mic In->Insert Send etc.) To create a test jig for the bench that essentially emulates all of the functions of the master section (like all of the Aux masters, for example) just seems like too much work.
2) Visual inspection and passive component tests: This can be done on the bench. First visual: Any burnt parts, loose hardware, switches with their tops popped off (I'm looking at you, ALPS SPUJ) etc. ?
Then, a visual of the electrolytic caps: Any bulging tops (or ends on axial caps), stretched skin, or standing taller than caps of same value (a sign that the end may have popped out). If you have questions about the caps, further testing with an ESR/Capacitance meter like the Peak ESR70 will give you a good idea if you can do spot replacement of individual caps, or if a re-cap is needed.
You can also test switches with your DMM. Lately, I have been finding that dodgy switches are quite easy to verify simply by use the Ohms setting and testing between contacts. If you see anything over, say 1 or 2 ohms, the switch is suspect.
IC Sockets: Do they hold the IC's firmly? Do they look tarnished? Giving each chip a push downward to re-seat it can break up oxide build up with a satisfying "snap!".
Connectors: Bent pins, dirty, tarnished, etc? Broken latch mechanisms?
And finally, a careful look at the soldering, preferably under magnification, can show up suspect joints, especially in older, hand soldered desks.
+1 to Brian's question about what make/model desk we are talking about. Chances are, someone on here may have designed, built, serviced or commissioned whatever you have.

 

[JohnRoberts]

Testing console strips on the bench, outside the frame is difficult to fully confirm every single function. You don't mention what desk, but 24 strips suggests its not a little un. Depending on the type of console inline or split you need at least one input, one master section, one sub master (if a split), and efx send/returns. And of course a console power supply.

You can start debugging/troubleshooting running simple music/audio through the input strips, but for serious work you want a decent sine wave source and the capability to monitor/measure the output level accurately.

Back in the 80s I designed a simple audio test set (Loftech TS-1) but you don't need a dedicated test intrument to get started.

JR

 

[Sturoc]

Thanks JR ,
Its one of your babies, an AMR 800 as we have discussed in another thread of mine earlier this year.
I pulled most of the input modules for cleaning and inspect and am ready to test each one as well as bus and master sections. The mainframe and P/S will be set up on another bench as well. This was delayed this year by travel / work and now finding a nice room to do the work in.

 

[JohnRoberts]

Good luck... be careful making repairs to those old single sided PCB.

JR

 

[Sturoc]

Do you have schematics? If so, please post it..

My console is a Peavey AMR 800 Split. Its designer John Roberts and I have discussed this console in a separate post earlier this year.
Here are the schems for channel module strip . JR has given initial guidance, so any tips on testing etc are also much aprecciated.

 

[Brian Roth]

A block diagram of the signal flow would be useful for us here.

I've worked on a few AMR desk over the decades....most recently in 2016 (?) in Kansas City. They are VERY under appreciated.

As others have mentioned, after carefully scrutinizing/cleaning each module put the modules back in the frame...and the fun (testing) begins. Any large format desk has a bazillion signal paths/functions and IMHO all have to be tested. Otherwise, in the middle of a session ..."Hmmm something is weird with the mid EQ on module 12" "Send 2 on module 3 doesn't seem to work" "Fader on channel 7 is scratchy" etc etc

The AMR desks I recall didn't have an integral patchbay, so you need the desk in an area where you can easily get back and forth from the front to the back (to change patching) while running the tests.

Bri

 

[ruffrecords]

Your analog scope is how old?

About half my age

Cheers

Ian

 

[Sturoc]

AMR 800 Blk diagrams

 

[gyraf]

..for quick confirmation of a channel among many being OK, I use a very-low and a very-high frequency signal for testing, then simply compare levels across channels.

10Hz and 30KHz are good candidates. This is my to-go setup. Very-low-freq is the first to go when electrolytics dry out, extreme hf can show loading problems and tired opamp drivers. But note that you'll need a voltmeter (or a scope) able to read these freqs

The test signals easily obtained with e.g. a 8038-based waveform generator - https://www.aliexpress.com/item/1005006630001609.html

/Jakob E.

 

[JohnRoberts]

..for quick confirmation of a channel among many being OK, I use a very-low and a very-high frequency signal for testing, then simply compare levels across channels.

10Hz and 30KHz are good candidates. This is my to-go setup. Very-low-freq is the first to go when electrolytics dry out, extreme hf can show loading problems and tired opamp drivers. But note that you'll need a voltmeter (or a scope) able to read these freqs

The test signals easily obtained with e.g. a 8038-based waveform generator - https://www.aliexpress.com/item/1005006630001609.html

/Jakob E.

Good general advice but OP wants to perform a full functional check. As I recall the test technicians took several hours to check out one console. We actually built them two soundproof booths so they could hear what they were listening to.

That series has many sends and to check them all requires having modules to send to.

JR