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HP339A distortion analyser
HP339A distortion analyser
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Old 17th October 2018, 06:02 PM   #791
RNMarsh is online now RNMarsh  United States
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Originally Posted by RNMarsh View Post
There is an Asian made clone of the HP-339A now. It does not look exactly like the 339A but similar and has all the same features and controls.

Attachment 709451

MCP DTM4120 - distortion meter, View distortion meter, MCP Product Details from Shanghai MCP Corp. on Alibaba.com

I have inquiry in to mfr as to their selling cost.

THx-RNMarsh
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Old 17th October 2018, 07:05 PM   #792
Audio1Man is offline Audio1Man  United States
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Hi All
The HP339A is a great instrument, however is has a few limitations, like BALANCED input (30 volt max), Bridged amps can burn up the instrument and output level 3 volts. Many users find this good for their work while other canít. Other instruments offer real BALANCED inputs like 200 volts and BALANCED outputs of 26 volts. Great instruments donít come cheap, used market prices usually out of the investment of most DIY just like Richard said.

My Tek AA501, SG505ís & SC502 & AP Portable One are hardly ever used I typically have 1 or 2 AP running on the bench with 2 or more PCís. I service & sell used APís
Duke
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Old 18th October 2018, 08:34 AM   #793
SyncTronX is offline SyncTronX  United States
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Originally Posted by 1audio View Post
The company seems to specialize in copies of nearly obsolete instruments: https://sep.yimg.com/ty/cdn/ldb-cdpackaging/CQ620F.pdf
Well I can tell just by looking at the pic of the instrument, that the scope's triangle and other waveforms aren't the actual scope pics. They are graphic additions.

It remind's me of the day in a tabloid sized automotive magizene Sharp had a pic of their LCD Projector showing either a car being welded or molten steel being poured. The image was striking and awesome. I contacted their rep in Detroit because I wanted one and we could use it with our client, General Motors.

I was talking with the Sharp rep about the order and asked how they got such great resolution with that projector? They confessed that they didn't, it was an actual picture they used in the ad and that the projector wasn't really as good as in the advertisement. They also confessed that anyone who purchased it was "pissed" that they couldn't get their projected images as good as the one shown and they've been very busy sending people their money back. It was a very bad marketing blunder on their part and advised that I not even buy the product because I too would be sending it back and demanding my money back.

Oh the promise of a great image, I still remember how vivid it was!

Cheers,

Quote:
Originally Posted by slbender View Post
Well I finally found out was is wrong with one of my 339a's. See pix. I think that is Sw4
@ Steven, BTW do you still have the broken off parts? If so, with some careful planning you might be able to repair it, them:
Epoxy board together.

Re-solder the trace, then smooth it out. Find some broken one somewhere and buy it cheap. ID which units you have/had functioning at their best then move parts around to those and have a dedicated parts unit. There was a guy here in Dallas that had removed some of these switches from his HP units but he wouldn't sell any of them--I asked. I don't know what he did with the ones he had or even if they were the correct configuration for the broken wafers.

Bummer, late to the party, but hey it's still a part nether-the-less (NTL).

Cheers,
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Old 22nd June 2019, 11:22 PM   #794
slbender is offline slbender  United States
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Smile Eight months later...

Hi sync,

I actually did buy another HP339a just recently. It has mediocre cosmetics, as every knob is broken or badly epoxied together and two are missing. Upon testing and looking inside, I find the internals look immaculate, like it just left the factory, but the set has an 11.0% - 12.0% distortion at most frequencies.

Using an external 1 khz. signal, from an Amber 3501, the analyzer section reads about -89dB (bouncing between -88 and -91) or around 0.0035% which is certainly in the proper range, so this HP339A has an Oscillator problem.

I just checked the 4 main power supplies - very close to +/-15 volts, and ripple between 0.4 mv and 1.2 mv. Considering that my Fluke shows 0.4 mv between two ground points on the PS board, the ripple may be lower, I am not in a shielded room, just in the dining room.

I checked temps in the set, with ambient at 79.6F most parts were 81 - 102.5 degrees, nothing seemed hot, worst was Q300 at 102.6 degrees. C306 was a bit hotter than the other 3 main caps in that area, so maybe a couple of lytic caps may be due for a change.

So I ruled out the power supplies, and the Analyzer, there is no evidence of prior repairs, but some trace of residue, like someone sprayed a "freezing spray" in a few areas (like at E1 and E2). I have to check the output on a scope, at the A1U1 test point, it is way distorted at the output bananna jack's on the front panel. I had bought a bunch of the LT1468CN8's from Digikey about a year back, and I have a few AD-747's which are similar too if it is a U1 that is the problem, but that is not even close to being verified.

Anyone with some suggestions, where to look next, I would be grateful for the help!

Steven
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Last edited by slbender; 22nd June 2019 at 11:28 PM.
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Old 23rd June 2019, 02:48 AM   #795
anatech is offline anatech  Canada
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HP339A distortion analyser
Hi Steven,
Can you follow the oscillator signal from the actual oscillator output to the buffer and then through the attenuator? It's a good use for your Amber. Some times there are problems with the LDR units.

-Chris
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Old 24th June 2019, 03:04 AM   #796
BSST is offline BSST  United States
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Hi Steven,

I can try to help.

As you mentioned, a peek at A1-TP1 would be a great first look. You didn't describe the appearance of the distorted waveform at the oscillator output, but I'll guess it's clipping on both positive and negative peaks. And most likely a problem in the oscillator amplitude control loop.

Would you describe what you observe at TP1 and at the various test points in the amplitude control loop, i.e. TP3,4,5,6,8? DC voltages, AC amplitudes, and waveform shapes are all of interest.

Good luck!

P.S. BTW, make sure to use a x10 scope probe. X1 probes with their high capacitance can provoke opamp oscillation.

Last edited by BSST; 24th June 2019 at 03:14 AM.
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Old 25th June 2019, 10:19 PM   #797
slbender is offline slbender  United States
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Default A few days later, distorted HP 339a

Hi BSST

OK, I have the set and a Sony 336 scope setup and I am using the 50 MHz. 10x scope probe within the A1 osc area.

Probe is currently calibrated and the Sony AC coupled.

Going to show waveforms on the testpoints. The photos in order are:

Front of Sony 336 scope
Body of Tek P6148 probe
Cal signal optimized on probe
TP1
TP4
TP5
TP6
TP8
(Somehow I lost TP3 when uploading them, hmmm.) Is it needed?

Steven
Attached Images
File Type: jpg Sony 336 Front.jpg (573.8 KB, 155 views)
File Type: jpg Sony TEK P6148 Probe.jpg (553.6 KB, 156 views)
File Type: jpg Sony 336 CAL.jpg (538.0 KB, 152 views)
File Type: jpg HP339a TP1.jpg (495.1 KB, 150 views)
File Type: jpg HP339a TP4.jpg (511.0 KB, 146 views)
File Type: jpg HP339a TP5.jpg (323.9 KB, 15 views)
File Type: jpg HP339a TP6.jpg (481.1 KB, 13 views)
File Type: jpg HP339a TP8.jpg (498.6 KB, 17 views)
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Last edited by slbender; 25th June 2019 at 10:24 PM. Reason: Lost a file
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Old 25th June 2019, 11:14 PM   #798
davada is offline davada  Canada
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The oscillator is not stabilizing for some reason. Check the TP for Jfet gate, what dc voltage do you have there?
It would be more telling to use dc coupling for now.
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Last edited by davada; 25th June 2019 at 11:18 PM.
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Old 26th June 2019, 12:05 AM   #799
BSST is offline BSST  United States
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Hi Steven,

David is right. DC voltages will be more telling at this point. Even voltmeter readings may suffice.

TP8 DC volts will tell us a lot. A wild guess is that TP8 will be a large negative voltage.

If so, a couple simple experiments:

If you use a grounded meter probe (or similar technique) to short the junction of R52 and C30, the oscillator should stop. (I've seen lots of warnings to not short Q2 case, so exercise caution.)

Similarly, if you ground TP8, the oscillator should also stop, as that will put Q2 into a low resistance state. If these tests behave as they should, then Q2 is probably OK. Would then measure U2C voltages at pins 12, 13, 14?

Last edited by BSST; 26th June 2019 at 12:13 AM. Reason: typo
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Old 26th June 2019, 07:32 PM   #800
BSST is offline BSST  United States
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Hi Steven,

I’m having erratic internet access at home and am uncertain I’ll be able to get onto the forum this evening. So I’m going to outline some thoughts and offer a few tips.

Based upon the TP8 scope waveform in your post, my best guess is that Q2 is biased into the off state, hence the guess that TP8 will have a large negative voltage near the -15V rail. The “short-to-ground” tests I suggested earlier are intended to test health of Q2, assuming TP8 is in fact a large negative volts as imagined. If TP8 is large and positive, Q2 is likely open, but I doubt this failure mode because of the TP8 waveform.

If Q2 is confirmed operable, the most likely culprit is U2 and the hope is to catch it “misbehaving” in-circuit. To this end, I suggest re-measuring the test points with DC coupling on the scope. Given that the oscillator is in clipping/overload, the anticipated waveform at TP4 is a replica of the TP3 ripple but larger in amplitude (x 2.47) and riding on a DC voltage of several volts. (BTW, once the oscillator is working properly, the saw tooth ripple will remain but average voltage at TP8 will be 0V.) If you don’t see a waveform approximately as described, U2 is highly suspect.

If U2A works correctly, I suggest exercising U2B and U2C using a troubleshooting technique I use frequently:

To test U2B, try to position your scope probe (or voltmeter probe) so that it joins pins U2 pins 6 and 7 simultaneously. This converts the stage into a unity gain opamp. The measured voltage should be a replica of the voltage of the + input--- in the case of the U2B integrator, 0V. Similarly, shorting together pins 13 and 14 should generate a replica of the TP6 waveform.

I hope some of this will point to the problem. Please let me know what you observe/find. Good luck!
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