How to test an optical converter ic (AL1401AG Wavefront)?

[camarada78]

I have a focusrite ADC card in my bench that is not sending signal out from its optical outputs. Both of them have zero output and no light is emitted through the adat cable.

After some measurements I have a suspect: the optical converters. A Wavefront/Alesis AL1401AG ic

- the powersupply is ok, all voltages are correct all around the board.
- My scope do catch digital signals on the IC input. Which is expected.
- also the internal clock is outputing a regular pulse, which is also expected.
- I dont have an external clock to test (would a signal generator work as clock generator for audio devices?)

What is the signal that i should have on the output of the IC? I imagine that it should also be a pulsating digital out.

What is weird is that both ICs are bad, because both outputs are bad, which is a little unusual but not impossible.

I cant share the ADC schematic due to a NDA.

any tips would be welcomed. have a good day

Leandro

 

[Khron]

(would a signal generator work as clock generator for audio devices?)

Very likely; 44.1kHz or 48kHz, 50% duty cycle, probably ~3V amplitude; definitely no more than 5Vpp.

You could of course scope out the outputs of the chips and see if there's anything going on. Even without any (digital) input signal, there should (normally) be plenty of transitions to see.

https://ackspace.nl/wiki/ADAT_project

I don't suppose the two optical transmitters have a separate power rail from the chip, that could be not-working?

 

[camarada78]

Thanks for the quick answer kron.

I scoped the outputs of both chips and have zero signals, no pulse, no voltage (but it is not shorted to ground).

They have only one power rail (pin 20) that is 5v and it is very stable without ripples.

I later suspected the reset function might be the problem, but the reset function is "active low reset" per datasheet and it is receiving voltage normally (5v also).

 

[ccaudle]

also the internal clock is outputing a regular pulse

Do you mean the word clock input to the AL1401 device? Did you verify the frequency is correct? Seems unlikely that it could still be running but at the wrong frequency, but easy enough to check with most scopes.

Any chance the input to the optical module failed and is holding the output low?

 

[camarada78]

Do you mean the word clock input to the AL1401 device? Did you verify the frequency is correct? Seems unlikely that it could still be running but at the wrong frequency, but easy enough to check with most scopes.

Any chance the input to the optical module failed and is holding the output low?

good guess.

The clock input to the AL1401 is giving me 4.1khz (not 44.1khz). according to datasheet it should be equal to chosen frequency. falls to 2.1khz when changing to 48khz sample rate.

I will investigate. thanks for the tip.

 

[camarada78]

scratch that. it was error on the scope. It is receiving 44.1khz, 48khz normally.