HP339A distortion analyser

[stevecooke]

I have managed to make a total donkey of myself and damage a HP339A distortion analyser that I have no documentation for. I inadvertently plugged it into 220V instead of 110V. Naturally the external fuse didn't blow before it damaged internal components. I live in Saudi Arabia so don't have a good repair shop here. The damaged components are diode bridges D301 and D302 and diodes D303 and D304. If someone has a parts list and ideally schematic I can access via PDF or via other internet means (or knows where I can find such information on line) I would be most grateful as I could then source bits for a repair. The parts don't have identifiable markings on them.
The instrument's owner will be coming back in 4 days and I'll be one dead donkey if it's not working.
Hoping someone can help ...EEE AWWW!

[soekris]

The manuals is online at Agilent:

Agilent | Product Library: 339A Distortion Measurement Set [Obsolete]

Best luck,

Soren

[kevinkr]

Unfortunately it is quite probable that there is collateral damage, it is unlikely that the diodes failed due to excessive voltage, (unless HP used very low voltage diodes) more likely that they died from excessive current due to damaged/shorted electrolytics and other parts in the power supplies.. If you are very lucky it might just be the diodes and input filter caps.

Once you do the repairs I would use a series ballast lamp on the mains, 60W or so to limit further damage in the event you did not get all of the problems the first time around.

IIRC Every 339A I have ever seen has a voltage selector switch on the back panel so that unit should probably be switched for 220V operation. (or the right voltage for Saudi Arabia)

Good luck!

[stevecooke]

Thank you for your replies to my post. I have downloaded the service manual and have smuggled the 339A home where I can replace components. I have a short across CR301 diode bridge output - could be the bridge, CR303 56V zener, 2 capacitors or U301 LM325H voltage regulator. Needless to say I couldn't get any of these except the capacitors in the electronic shops downtown. Mail order will take a longer time, obviously. I will be unsoldering bits tomorrow to try and isolate the short and just pray the transformer isn't damaged. (The circuit diagram doesn't show secondary voltages at the transformer so I don't know what DC to expect at the diode bridges CR300 and CR301 outputs). Trying to get a replacement transformer quickly would be like trying to find a UK MP who hasn't fiddled expenses. Will post again if I manage to fix it.

Steve Cooke 22 April 2010

[stevecooke]

After connecting the unit to 220V when it was set to 120V at the rear I found 56V zener diode CR303 was short circuit, happened before the rear fuse blew. This diode protects the Power supply IC for the meter circuit.
Naturally I can't get one in Saudi off the shelf so am waiting for one from the UK. As the diode is for protection against overvoltage only I just removed it for now. The unit now works fine but has less protection against overvoltage until I receive the diode. A lesson learnt!
Thanks again to those who replied to my original post and a big thank you to Agilent for making their old test equipment diagrams available.

[rize]

Hi Steve,

I'm glad the damage was not serious and hopefully by now your 56V zener arrived.

I'm interested in DIY audio and after some research concluded that a good distortion analyzer with a sine wave oscillator will be very useful testing or building power amps. Initially I was looking at hp 239a which has impressive specs but unfortunately it doesn't have distortion measurement, hence my interest in finding a 339a - they're quiet expensive. I found one unit except most of the labels on the dials have worn off. I thought this was odd, I'm wondering if some solvent was used to loosen up these controls and it wiped out the scales. The unit apparently powers up but the seller claims nothing about testing and doesn't accept returns - typical fleaBay sales tactics.

May I ask what your application is where 339a is useful ?

Cheers

[gogowatch]

Hello Steve,

I got one HP339A and wonder whether is it normal for the instrument to behave like this on powering up.

When I turn it on, no matter what the input scale is, the meter swing to the very far end, then I turn it off immediately because I don't want to damage it. I wonder I should let its power on and let it have a chance to settle down.

Does your HP339A behave like this on powering up?

Thanks in advance.

Cheers,
WK

[audiohead]

HP pulled a boner on the meter drive circuit.

Art

[kevinkr]

Originally Posted by gogowatch

Hello Steve,

I got one HP339A and wonder whether is it normal for the instrument to behave like this on powering up.

When I turn it on, no matter what the input scale is, the meter swing to the very far end, then I turn it off immediately because I don't want to damage it. I wonder I should let its power on and let it have a chance to settle down.

Does your HP339A behave like this on powering up?

Thanks in advance.

Cheers,
WK

My recollection is that it does - I used one for the entire decade of the 1990s, but not since, so YMMV..

[dchisholm]

Originally Posted by kevinkr

My recollection is that it does - I used one for the entire decade of the 1990s, but not since, so YMMV..

That's the behavior I also recall from the early 1980's. Yes, it IS very disturbing to see that needle peg against the high stop.

Dale