Solo isolation issue >>SOLVED<<

[oyanliz]

Hi all,

I have been reading threads about simillar issues, but I still do not know how to start fixind my issue.

The console was working perfect until last week we remove a stereo strip for checking the input card (there was a difference between left and right signal input). After pull out the strip, we switch on the bucket where it was installed the strip and solo isolation started failing in all channels.

When solo isolation starts failing, we switch off and on any of the buckets and everything comes to working fine again. But anytime starts failing again.

The console does not have multiplex cards, computer jumpers are installed and each channel has the multiplex card jumper bridge done in the motherboard.

Would be a ribbon cable between buckets? Should I start checking from other things?

Thanks in advance.

Regards.

Oihan

[oyanliz]

Hi,

I have replaced the 20 pin ribbon cables between buckets, S3E cables. Still the issue is there. When I switch off a bucket, the solo isolation works fine for switched on buckets. Does not matter wich bucket is shitched off, if any of them is switched off the others work fine.

It is definetly something coming from the PSU?

Thanks in advance.

Regards.

Oihan

[oyanliz]

Hi all,

We have tested with other PSU and problem is solved. So the problem is in one of our PSU, the voltage rails are not trimmed propertly. I am able to measure +20v and -20v rails in the 651 mother board, but I do not know how to measure +48v and The differencial between +18v and +12v. I do not see the tracks of +12v and +48v. I try measuring them around S20E connector soldering joints but... I do not have a clear idea of what I am measuring.
bellow +6V and this caused intermitent functioning of solo issolation.

If someone could explain in detail hor to measure rail values on the 651 module... I would be very gratefull.

Thanks in advance

Regards.

[amillar]

Hi,

This is how I used to do it on the 651 (from memory):
Measure on the edge connectors of the '33 and '34 cards on the 651 backplane.

Starting with the '34 card (nearest the meter bridge). The last pins 53, 54, and 55 are 0V and are very obviously joined together - this gives you a reference point.

From pin 52 to 55 should be between -18 and -18.5V
From pin 51 to 55 should be between +18 and +18.5V
From pin 51 to 49 should be 7V - as near as you can get it

Now moving to the next card, the '33 card
From pin 47 to 55 should be +48V - somewhere between 47 and 49V.

Be careful - it is easy to get your meter probe to short circuit pins 52 and 53, or 51 and 52.

Wherever you measure it, do NOT measure and adjust between the 11V and 0V connections, ALWAYS measure and adjust between +18V and +11V to be 7V.

Ignore the fact that the service manual mentions "20V" and "13V" on the backplane connectors, that was only true for the very early (about pre 1981?) desks. It was quickly realised that 5534s didn't like being run at +-20V for very long and were dying too quickly. (Actually it might have been the TL074s on the 10 card that died...anyway still not a good thing.)

Hope that helps,

Cheers,

Andy

[oyanliz]

Thank you so much Andy.

It is very kind of you!!

Regards!