Hi guys, I want you geeks zo look in your magic crystal electric ball.

The console was decomissioned by me out of a protools based studio.

My studer doesnt pass any usable signal from in to output. DAW -> ssl alphalink -> tape reproduce

The inputs are clipping (clipping led) easily (tape return and line).

I can monitor output on my ADC with a lot of noise (mytek reporting a lot of led activity. I have no mixer output but I can hear something distortet on the sum output (the one that goes into the mytek) from the desk.

The sound I can hear sounds like a echoish distortet crosstalk.

I know it can be everything...

What bugs me the most is the nonexistant headroom on the input channels.

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Hi George
There may be a number of things going on.
Your convertors are putting out too much for the inputs of the desk. I haven't read the specs but it may be simply too much level. peak output may be +24dBu from convertors but the dsk may only be happy with 20 or 22dBu. Line sources used to be typically tape or 'grams' for which the 'average' level would be quite low compared to some convertors and the machines themselves although capable of high levels, would rarely be called to deliver as the tape would be getting towards saturation.
Secondly, are the power supplies of the desk working properly, for example is one 'rail' running low voltage?
Third, are you sure it is wired correctly?
On the basis that it was at least working quite well in it's last 'home' it is unlikely to suddenly 'stop' working.
Last, should there be some insert linking that you have forgotten to reinstate?
I think you said it has a patchbay, is that connected to the right place?
Matt S

the inputlevel on the console should be ok. you know it's not like 2 or 4dB are missing. it's instantly distorting.

I can imagine that a rail is not working ok, or that the caps have dried out. the caps are 22 years +. the console was 24/7 in use, then decomissioned and stood still for 3 years.

let me check, and I will report back.

thanx!

Hi George
It sounds so bad that it's cause will be fairly obvious. I would doubt it is as 'subtle' as dried caps to be such a problem.
Matt

PSU is a good place to start. They are easy to check on those desks.
Is the problem identical on every channel?

ok.. here we go.

the PSU had a faulty PCB between transformer and DC-converters. resoldered the joints and voila.

12 out of 18 channels recapped.

audio is going trough it! headroom ok.

stabilizer cards are recapped too.

will report back. right now she is 80% working (RTF meter is not, some things not tested yet).

cheers
George

Great to hear that the PSU fault was not that bad.

Thanx a lot for the excellent channel recapping job Jensenmann!

Appreciated.

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Since George got his problem sorted, I'll just go ahead and hijack this thread then...

Here's my situation:
I finally got my Studer 902 in the control room(though I had to chop off the stands to fit it through the door).

I've been going though the desk for the past week or so and I've gotten all the mono input channels working. Also the bus outputs(1,2,3 and 4), and the AUX outputs(1,2,3 and 4) work just fine. The talkback mic and routing works(except TB out C and E).

Here's my current problem:
I´m having problems with the control room unit 1.920.420

I´m only getting a very weak signal to the headphone outputs and only from master bus 2. Also the units source selectors don´t seem to affect the sound coming to the phones(or the CR bus). Also the signal is reversed(bus2 is coming out of my left earphone).
I have to turn the volume knob all the way up and even then the signal is very low. I eyeballed the unit and all the components seem fine, no blown caps or burnt resistors and all the solder joints look good...

I get a good and solid signal to the PFL bus and studio/PFL unit, so I can monitor the input channels through PFL but I'd like to get the CR unit working as well...

I have no idea what the problem here is, please give me some suggestions where I should start troubleshooting.

Thanks,
Tomi

Hi
If your Studer uses the 4136 Quad op amps, I have some little adaptor cards available that allow you to use 'modern' surface mount chips in that position. They are 'plug in' if your modules have the original chips on sockets. Note that the 4136 is about the only quad op amp that uses this pin layout so the TL074, MC33079 or whichever will not work as a plug in replacement.
Matt S

Thanks,

So you think it's the opamps that are causing this? How would I confirm this?
I just checked the schematics and there are no 4136´s in the control room unit. There are RC4559´s and NE5532´s...

EDIT: There seem to be RC4559's and NE5532's in the studio/PFL unit as well so I'll start swapping those tomorrow to see if it has an effect...

I fixed 99% of my 903a problems by replacing 5532 and 5534 ic's. They just seem to blow every once in a while.

Hey, been waiting for you to chime in!!!

Really? How about the other opamps?

How's your board doing? I really like what you did with it(been reading your blog...).

I'll be doing some testing tomorrow and will post back how it is going.

Are you still looking for parts?

Well I just swapped all the 5532´s in the CR unit with no change, so it seems they are not to blame...
Any other suggestions?

Hi
Considering the internal complexity most 'op amps' since the '741' varieties are incredibly reliable as long as the power rail voltages are not exceeded and the circuit design does not deliberately 'stress' them.
Failures are far more likely to be elsewhere in terms of poor connections or 'short circuits' which may ultimately result in component failure.
Rather than becoming an 'expert' through watching a chip being changed on Youtube it would be better to learn some basic failure modes of various components, at which point you will discover than probably 70 percent of 'failures' will be mundane 'poor connection' related rather than anything 'esoteric'.
Matt S

Ok, thanks.

So what would you suggest I do next?
Here´s what I can tell you so far:
-the channel reverse switch works(changes left to right and vice versa)
-the ch1 phase reverse switch works
-the balance control works
-the mono switch works(I hear the faint signal in both earpieces.
-the headphones vol control works

-the input selectors have no affect on the signal

I have to turn the channel fader, master fader and the CR volume pot all the way up to even hear anything. As if I was listening to the signal through the ground bus...

Hi
Use a multimeter first on DC to check supplies are what they should be, then on AC with a tone inserted to find out where your signals 'stop'.
Matt S

Thanks,

I guess it´s time to start tracing the signal...

Though I don´t have a true rms multimeter, just your regular multimeter so we´ll see if I can work with that... No, can´t measure the AC...

Hi
You only 'need' a true RMS meter if you are attempting to measure NON sinusoidal signals as most (practically all) meters are 'calibrated' for a sinewave.
You have to pay good money for ANY meter to be 'accurate' beyond about 400Hz but for the purposes described here almost anything will do as you want to be looking for a signal of say half a Volt to a couple of Volts, and comparing it to practically 'nothing' where the signal has stopped.
Matt S

Ok, now I´m totally lost here.

I have no idea where the signal goes from the master faders. The problem must be after the master faders because I´m getting the signal ok from the outputs of 1,2,3 and 4.

I know there are some distribution cards under the desk, do these split the signal to the outputs and to the CR unit?

If that is the case then I would think the problem is there?

I´m ok at reading/following schematics but I´m no EE so bear with me...

Thin, leaky signals can be really bad caps. Just because they do not look blown or puffed up, doesn't mean they are still ok. Studer used a lot of Frako brand caps and I've seen those fail often.
Best,
Ike

Yep.

I think it was back in the mid-'80s when it finally dawned upon me that when I was called upon to repair a tape machine with a complaint like: "It sounds weird", "No low end", "sounds muffled", "it distorts" (or the like), I could almost ALWAYS save a whole helluva lot of time, effort, and energy just by making it "standard operative procedure" to start by just re-capping any analog tape device (or part thereof) which was displaying those sorts of symptoms.

...And then putting the machine through a complete alignment procedure.

Turns out that damn near every time I handled it this way, I would be in the door, problem solved, and quickly on my way to the next "disaster" in LESS time than performing an actual "diagnoses and replacement" (...Usually a bad CAP, or two ...or three).

...And since most ALL the caps in such a device are usually about the same age (and we have now replaced them with new ones), I also avoided getting quickly called back in order to service the same damn machine at some annoyingly-too-soon future date.

Even fairly expensive caps are often quite a bit cheaper than all the gasoline for repeat visits, extra time spent, and how your clients perceive the quality of your work. (They like it when things STAY fixed!)

.

Thanks for the advice, I'll be changing the caps tomorrow.
I'll report back...

So, good news and bad news:
Good news- all the caps are changed!
Bad news- still no sound...

Ideas?

Hi Tomi,
Having re-read your original post, it sounds to me like you are not getting signal into the CR module. I'm not very familiar with the Studer desks, so I can't get too specific but a couple of things come to mind:
1) Weak or missing master signal: In most consoles this is always routed to the CR section. Sometimes you have to select it as a source and in other cases, it's always there until you select another source (2 Track -A etc).
This signal has to be sent from the 2-mix o/p somehow. You may be right about the distribution cards under the desk. At the very least they should be inspected / re-seated (or really, they should be found in the block diagrams and verified or rejected as the source to the CR section). These could have a bad cap or two, or a bad 5532, or both. I've seen lots of 5532's have high DC offset on their outputs, cooking the coupling cap following. In any case, you have to figure out how your 2-Mix gets routed to the CR section. What about metering? Does the 2-mix meter correctly, or does it reflect the same issues you hear in the CR section?
2) External switches doing nothing: These signals have to be sourced somewhere. Usually, they will go to a multi-pin on the back of the desk (Tuschel, in this case?) and then to the patch bay and then to the selector switches. I worked on a Studer desk a few years ago that initially confused me because at first glance, it looked like all of the i/o was on XLR's. After a while, I noticed that there was a row of Tuschel connectors, out of site, beneath a frame member, and that the wiring to all of these had been cut when it was removed from the broadcast studio. Since some of those connections had been insert send / returns to a remote patchbay (where they were normalled), things started to work a lot better once those connections were bridged over. So, have a look for your external connections.
Best,
Ike

Thanks for the reply Ike!

The meters aren't connected as I haven't found a pinout for the meters yet but I can tell that the signal is healthy out of busses 1-4 since the output from behind the console is ok. As are AUX1-4.
Actually busses 1 and 2 are split into 4 different outputs that all work and I think this is done by the cards under the console. Busses 3 and 4 both have one balanced output. Also there is mono 1+2 output that I haven't checked yet.
I think I checked the AUX outputs(I think...) as well and they were ok.


Pretty much all of the connectors are siemens type, I'm planning to hard wire XLR inputs for mics and outputs for the busses and auxes.

Since all the outputs actually work(except the CR out of course), and all the busses are outputting a healthy signal I can't stop thinking it has to be in the input of the CR unit(mainly the source selector).
The unit has source selector for 15 different inputs that you can select from. Anything from master busses to external sources. There's a also a PFL override, when you solo a channel and have "TO MONITOR" switch on in the studio/PFL unit, the CR unit is fed the PFL signal.

And no matter which source I have selected(haven't tried the external ones yet) theres no signal.

Oh well, tomorrow we shall continue...

.

...Well, at least you've got the caps outta the way.

I'll bet you find the culprit soon.

(Sounds like you're on the right track.)

.

So to be clear about this, the CR output to the monitors works?
iz

No.

CR output does not work.
See my last post:
"...Since all the outputs actually work(except the CR out of course)..."