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Old 21st December 2014, 05:33 PM   #1
djupdal is offline djupdal  Norway
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Default HP 339A problems

I just got myself an HP 339A distortion analyzer. First I was happy as it seemed to be working, but now I have discovered some problems with it. There seems to be at least two different things:

- Performance: When connecting a coax between output and input, I usually read between -60dB to -80dB. That is bad. It seems to have problems with nulling, it sometimes takes a long time to settle on the lowest reading (sometimes not at all). Sometimes it seems to help to play with the switches when it cant find the null.

- The meter: Usually it is OK, showing approximately what I expect it to (comparing to other instruments etc). But sometimes it just stops working and shows apparently random values. Corrects itself after a power cycle.

Before I spend christmas trying to find the causes of this, does any of you know of "typical" problem components in these units that I should check first? I think the oscillator is OK, at least as far as I can tell by looking at the scope, so the problems are probably somewhere else.
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Old 21st December 2014, 08:05 PM   #2
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Default Where to start?

Hi, I haven't had any problems with my HP339a (grin)
but if I did, you could start at post # 401 from RN Marsh
and post your distortion reading. That is on the
HP339a Distortion Analyzer thread.

Post # 401, then post # 410.

That is a start.

For reliability replace the 4 electrolytic's
in the power supply to 105 degree types.
Carefully clean contacts, switches, and knobs.

Avoid over spray of the air capacitors.
I covered mine when I was cleaning it.

What kind of shape is it in?
What did you get it for?
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Last edited by SyncTronX; 21st December 2014 at 08:08 PM.
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Old 22nd December 2014, 08:31 AM   #3
djupdal is offline djupdal  Norway
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Thanks

I have seen that huge thread. Did not read all the posts there because I though it was more about improving the 339A beyond the original specs, but I see I was wrong.

The 339A is in good shape. Looks OK for being so old. It even had the warranty void stickers on the screws. Some of the switches has been repaired, but it was done well so I dont mind that. I paid 350USD on ebay.
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Old 22nd December 2014, 08:50 AM   #4
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djupdal,

You are are in good hands here, there are some really good people
that will help you out. Me, I'm just trying to get mine working properly
and make it better.

Make sure you get a manual for it you can buy one online
from <name> or buy and original hp manual. For me, I bought
a real one, then copied the schematics on Tabloid sized 11 x 17
80 - 100 pound card stock.

See what the analyzer will do first. Then do the power supply.
It probably won't make a difference other than peace of mind.

Then see what it will do again. Follow the steps that RNMarsh
wrote out, they worked for me. If you need help you've got
RNMarsh, RichEEM, Davada, Demian, SkiDave, DennisMiller,
Me, others drop by from time to time. These are bright bunch
of get up and go guys. I can't keep but they don't seem to mind
me tagging a long and when I get lost, they help me along my way.

Nobody really complains about anyone either, it is a nice group
of professionals and wannabes. : )

This is the link to the shorter thread:The post #401 and #410
http://www.diyaudio.com/forums/equipment-tools/165481-hp339a-distortion-analyser.html

The long thread is the low distortion oscillator thread.

Then there is the grand daddy thread that's even longer, but another forum.
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Last edited by SyncTronX; 22nd December 2014 at 08:55 AM.
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Old 9th January 2015, 10:33 PM   #5
djupdal is offline djupdal  Norway
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SyncTronX, sorry for answering your kind post so late.

I fixed the meter problem. It was a bad opamp (A2U6). Changed that to a DIP version of the 741, it now works very well.

Regarding performance, after cleaning switches and calibrating (as good as I could with my equipment), I get close to -90dB on most switch positions (when connecting it in loopback). This is not according to spec, but close enough to be useful for me. I will therefore leave it as it is and instead start using it

Good luck with your 339A project.
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