HP8903A Audio Analyzer repair

[mark_maher]

Hi!

I recently picked up an HP8903A Audio Analyzer, which is not measuring AC voltage level properly. I have found a pair of 1/16A glass fuses on the input amplifier board (A2), one of them is blown. I can't find any schematics for this model, and do not want to put another fuse in without understanding what could have caused it (especially as I don't have any 1/16A fuses...) . I also note that there are no fuses on the newer models.... Maybe they are just prone to fatigue?
Has anyone got schematics, or experience of this problem?

Any advice apreciated!

Mark

[chihaxinh]

hi mark_maher

I thing owner equipment make overload vol input device ! Likely measurements in Anode tube in VAS stage !
Pls take out and take picture for other member review

Best regards
Nam Nguyen Hai

[singapol]

HP8903A service-21Mb 450pg:

http://www.schematicsunlimited.com/h/hp-agilent
http://www.schematicsunlimited.com/h/hp-agilent/hp-8903a-audio-analyzer-service



HP8903A_errata-
http://exodus.poly.edu/~kurt/manuals/manuals/HP%20Agilent/HP%208903A%20Operation.pdf

Old 8903A?
http://www.electronicspoint.com/threads/hp-8903a-audio-analyzer-schematic.230344/

[dacman]

A2F1 = 1/32 A (or 0.032 A, 250 V).  On HIGH signal input line.
A2F2 = 1/16 A (or 0.062 A, 250 V).  On LOW signal input line.

Note that the analyzer has a specified input range of 300 V, whereas the input fuses have a rating of 250 V.

Check C2 and C3 on the A3 card (and other aluminum electrolytic capacitors).

[mark_maher]

Thanks for your replies! The link to the service manual was very helpfull. I changed the fuses, and now the instrument works as it should. Looks like it was an overload from the previous owner..

I'll check through the caps as you suggest.

Thanks again!