HP 8903B Audio Analyzer
This page covers the ins and outs of our HP 8903B Audio Analyzer.
This is a great piece og test gear, allowing us to make numerous measurements on all our gear, such as THD (Total Harmonic Distortion), frequency response and much more.
We got this analyzer a while back and we though we cover our experiences with this piece of gear, the overhauling we carried out as well as some basic adjustment.
This is to help other owners of the 8903A/B.
Looking at this unit, with all its buttons and myriads of testing ability, it can be a bit daunting at first. We went through a steep learning curve and are still learning of what this analyzer can do.
We also have a full set of service and operation instructions, with all the circuit diagrams as well a complete set of test and calibration procedures.


April 2020:
The first thing we did when we got this unit, is open it up and gave it a good clean out, mainly dust. We removed each pcb and cleaned each with an air compressor, followed by the chassis.
We also gavce the front panel a good wipe down with de natured alcohol. It came up almost as good as new!

The we had a good look over, to make sure there were no obvious damaged ares, darkened spots on any of the pcb, just a good visual checkover.
Our unit was made in late 1991, so the main power supply capacitors probably needed replacement.
There were another three smalled axial lead electrolytic caps on pcb A3.
We decided to replace them all. It is piece of mind. Electrolytic caps have a lifespan of around 20 years or so, so it is a good insurance to raplce them with new units.
The three large caps are made up of two values. Two are 3900uF @ 40V and one is 15000uF @ 25VDC. We replaced them with 3800uF 50V and 14000uF 50V, we got those from Mouser.
On pcb A3, two are 20uF 50V and one is 100uF 50V. We replaced them with equal value caps, also from Mouser.


Once this was done, we powered it back up and went through some checks. This is detailed under 'Basic Functional Checks', section 3-5 in the 8903B operation manual.
You will need an oscilloscope as well.
Anyway, we had an issue with the output voltage. Setting it to 1.0V, we only got 0.545V. The frequency was OK. So, all following tests were also out.
Now, we also happen to have the 8903A operation manual. There, the above tests are called 'Operator's Checks', section 3-10. In that section, they are actually point to fault finding instructions if the readings are out, and it just so happened that a low output voltage level was covered.
So, we went ahead and follwed those fault finding isntructions as set out in the 8903A Operator's Checks section 3-10.
Not really sure why they did not add these in the 8903B manual....because without those fault finding hints, we would have had a heck of a time trtying to figure this out.
So, we recommend that you obtain BOTH the 8903A and 8903B manuals!!
In the end, it turned out that the calbration was out by a small amount, as detailed on SHEET 9 in the 8903B manual. Once we re adjusted those areas, bingo, it was reading correclty and we got 1.000V output level when 1V was selected.

All other areas and functions, so far, seem to be good.


As we get into more detailed operation of our 8903B, we will cover those here, so stay tuned!