888 fails to power up

[~rf~]

Any help would be much appreciated. Even if it is confirmation of power supply failure.
Today I had a situation happen on not one but 2 888 i/o interfaces. When I powered up one of the 888 interfaces, it lit up briefly then went dark. I don't use this old digi rig much anymore. when I powered on the 1st 888 it lit up briefly, went dark and then began to pulse like a metronome thru the outputs. I then powered the second and it seemed to be fine, so to use the system I disconnected the master slave cable and the 1st 888 cable and repowered the 2nd 888. It failed within seconds. These units worked fine just several months ago.

I have good power and these units are mostly disconnected from a/c when not in use to avoid potential damage from spikes or strikes.

[~rf~]

I opened up the 888/24 I/O interface that failed first. Did some troubleshooting and when I disconnect the output ribbon cable, it powers up.
Is it possible that something has failed in the output circuit?
Does the power supply have a circuit for the output bus?

I have another older 888 16 bit that has the same symptoms. I can really hear the clicks coming from something somewhere either on the main board or the power supply.
Does anyone know what has failed and if this part is easily replaced/repaired?
Is there a schematic available for these older outdated interfaces?

Thanks

[mrhappy]

It's strange that all 3 of your interfaces have all of a sudden developed the same problem... Are the 888/24 interfaces connected using the 'Y' cable? If so maybe you could try a different interface cable to see if that is causing a problem??

Are the interfaces  connected directly to the Mac or through a expansion chassis?

[mrhappy]

First thought went to failing caps but it seems odd that they'd fail on the same day... 

[Astroman]

yes, so much synchronity would be very unlikely.
Sometimes unplugging/replugging cards and bus cables helps with vintage audio gear.
(I have a Creamware DSP system of similiar age that occasionally has contact 'symptoms')
Be careful not to touch contacts with fingers.
Pure ethanol (from the chemistry) is a good cleaner, but beware of the stuff used to light up grills, it contains some oily components.

Of course a (partly) failing PSU can have influence on output drivers and it may introduce electric noise into the circuit.
My 882 has a kind of suspective power-up noise (low level deaying beep of a second or so when regulation swings in), but no flaws in performance yet.

[oldtimer]

In addition to re-seating all Digi PCI cards, and reconnecting the internal Digi ribbon cable, I'd suggest running DigiTest to identify any potential problems at the source. Of course this can be a catch-22 situation, because DigiTest will fail if it's not receiving clock from the 888/24 interface.

[~rf~]

It's strange that all 3 of your interfaces have all of a sudden developed the same problem... Are the 888/24 interfaces connected using the 'Y' cable? If so maybe you could try a different interface cable to see if that is causing a problem??

Are the interfaces  connected directly to the Mac or through a expansion chassis?

These symptoms also happen when the I/O is in stand alone mode.
I have 3 888's and one is still a functioning spare. When I went in yesterday #2 powered up and stayed on. I suppose I just got lucky. The 1st one to go down is still down. I have it open and have been checking voltages from the power supply leads. All power is good and within range of 10% of PSU spec, although I suspect a cap on the negative side of the power supply. All the power is good until I plug in the ribbon cable on the output side to the main board. That's when it all goes in the crapper.

.... Of course a (partly) failing PSU can have influence on output drivers and it may introduce electric noise into the circuit.
My 882 has a kind of suspective power-up noise (low level deaying beep of a second or so when regulation swings in), but no flaws in performance yet.

Astroman, any ideas on which caps power what circuits?

For what it's worth, I have had a user in the Avid forum suggest caps as well.