hp8903a repair needed

[joustman]

Hi,
I have an hp8903a audio analyzer that does not display the proper voltage reading on input signals. I'm wondering if anybody has any experience in this area?
I have the schematics and can start poking around. I do not have board extenders which would make this task a little easier. The meter is way off so i don't think its a simple adjustment. Using a fluke it seems the output at least is accurate,
Thanks for any advice in advance.

 

[gootee]

If you don't have the full service manual, get it. Check at agilent.com. If it's not there try the "boat anchor manuals archive" (BAMA) site.

 

[joustman]

i have the full service manual.

 

[macboy]

At the input are a series of attentuators and a series of gain stages, each of which may be switched in or out depending on the detected signal level. You can check the level at each stage to determine where the level goes wrong. The service manuals are great, they have procedures to troubleshoot just about every circuit, including the inputs. Follow the check procedures! They include the use of special codes which override normal operation, and they describe what you should expect to measure at various test points, have frequent references to the schematics, and even suggest where to look for a fault when some test point doesn't measure right.

 

[macboy]

You won't need the riser card. Many of the test points and adjustments are located at the top of the board for easy access. Internally all boards plug into the chassis sort of like how PCI cards plug into a motherboard. If there is a test point that is obscured, you can remove the board (input board), attach some wires to the test points, and replace the board. You can then power up and take the measurements from those leadwires.

 

[joustman]

ok I'll give it a try. hopefully tonight.
I'll let you know the results.
BTW my email is [email protected] I live a little west of Ottawa in Almonte.
I build Tube Amps for one of my hobbies which is why i need this thing. I've been dying for an audio spectrum analyzer and its almost within my grasp. all i need to do is fix this and find an HPIB interface card/dongle.