Sirius 24 Analogue Output Voltage Low

[AlRamsay]

Hi,

I've got a Sirius 24 that is not outputting the correct voltage at the analogue output.  On a working desk, I am reading 0.23V-10.08V on the analogue output.  On the faulty desk, I am reading 0.82V-2.80V, this is also reflected in the output LED being significantly dimmer than it should be at full output.  This fault is common to all channels on the desk.

Can you give me any guidance on how the output voltage is derived, is there a voltage regulator I should be looking at?

Kind regards

Alasdair

 

[iank99]

@AlRamsay - there isn't a voltage regulator for the output rails per se - the voltage is derived from a D to A convertor that feeds an op amp (IC39) who's output voltage is set by a small resistor network selected by the output voltage selector link. The op amp is supplied from one of the internal 5v rails which is regulated by a conventional voltage regulator that's located near the battery, the 5v rail will need checking.

There's a possibility that the battery has leaked at some point & whilst the initial corrosion as cleaned - some of the battery chemicals have run along the PCB tracks & damaged them - I've repaired a couple of Sirius with similar corrosion issues, the stuff can spread like crazy.

You're going to need a schematic to fault find and I'm happy to send you one but I won't post it here - if you'd like to eMail me    ian at serviceguy.co.uk then I'll send you a copy.