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 Post subject: HP 5383a frequency counter problem
PostPosted: Sep Fri 24, 2021 2:59 am 
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Joined: Jan Sun 26, 2020 6:17 am
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I recently got this 520MHz frequency counter and decided that I was going to power it up and test instead of putting in off to the side and letting it collecting dust. However when I powered it up, it displayed all zeros except for one segment which maybe hard to see in the photo. This segment glitch only happens on the .1s and 1s settings so maybe something is wrong with the display? It also does not respond to any kind of input. Any advice on troubleshooting this thing?


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Last edited by GoldenAgeOfRadio on Sep Sat 25, 2021 12:59 am, edited 1 time in total.
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 Post subject: Re: HP 5382a frequency counter problem
PostPosted: Sep Fri 24, 2021 4:44 am 
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Location: Lexington, KY USA
Get the manual. That will get you started, at least.

There is an official vintage HP test equipment manual download site. Someone may have a link handy and post it for us. Google will find it, if you want to get it now. Then post the link here, so everyone can be looking at the same print.

Ted


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 Post subject: Re: HP 5382a frequency counter problem
PostPosted: Sep Fri 24, 2021 5:20 am 
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You mean this?

http://hparchive.com/hp_equipment

or better yet, https://nscainc.com/wp-content/uploads/pdf/A_5382A.pdf


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 Post subject: Re: HP 5382a frequency counter problem
PostPosted: Sep Fri 24, 2021 7:41 am 
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Thanks!


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 Post subject: Re: HP 5382a frequency counter problem
PostPosted: Sep Fri 24, 2021 11:49 am 
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The manual, typical of HP, is excellent. The troubleshooting chart should get you immediately to the problem with the input. The display issue could be any number of things, but it's pretty straightforward and might be covered in the troubleshooting chart as well.

If you have a scope, finding where the signal is going astray should be pretty simple. Fixing it, may or may not be lol. HP is high quality stuff of course, but I swear they were in a race with Tektronix to see who could use more circuitry, components, and servo loops in any given piece of gear.

That said, once you do get it fixed, you will know all about how it works :)

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 Post subject: Re: HP 5382a frequency counter problem
PostPosted: Sep Fri 24, 2021 9:38 pm 
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Location: Dallas, TX
One of the display digits might not be completely seated in the socket. Small instruments like this sometimes get dropped. A company might have literally thrown it in the dumpster when it stated to act up and they get a replacement.
The all zeros is a separate problem. Could be the crystal timebase oscillator is dead.
Once you get it open one of the first thing to do is check the power supply voltages. The one I have had evidence of the rectifier bridge being replaced. If I recall I replaced the power supply electrolytics.
I would stay clear of the input circuits if at all possible, circuits that turn frequencies as high as 500MHz and at low levels into digital signals were pushing technology at the time. Some unobtainium parts now.
The pictured counter is a 5383A, I have a 5382A that only goes to 225MHz.

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 Post subject: Re: HP 5382a frequency counter problem
PostPosted: Sep Fri 24, 2021 9:59 pm 
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The photo shows that the input impedance is set to 50 ohms which can load down a high impedance signal source (if that was what you were trying to measure). Try setting the impedance switch to 1 meg and see if that works better.


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 Post subject: Re: HP 5383a frequency counter problem
PostPosted: Sep Sat 25, 2021 1:08 am 
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Note also the 50 ohm input is FUSED. And there is a switch on the back that must be selected to internal reference to work. So I guess the next thing is to open er rup and see what you can see. You will probably see alot of parts with HP numbers on them which can make replacement a challenge in some gear.

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 Post subject: Re: HP 5383a frequency counter problem
PostPosted: Sep Sat 25, 2021 3:53 am 
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I had one of these counters that had intermittent display problems which cleared up when I resoldered the board. While you are doing that you could try swapping the display with the missing segments with an adjacent one to see if the problem follows. If so, a replacement display is needed. The displays are multiplexed so problems in the driver circuitry usually show up across multiple displays, not just one.

And yes the switch on the back has to be set to internal reference or you will just get zeroes.

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 Post subject: Re: HP 5383a frequency counter problem
PostPosted: Sep Sat 25, 2021 4:22 am 
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Thanks to Notimetolooz for pointing out that I've got a 5383A. I have found the correct manual online here:

https://bama.edebris.com/download/hp/5383a/hp5383a.pdf

Just from some initial continuity testing around the displays, segment F on display number 6 is 100% dead. Fuses are ok and the INT - EXT switch on the back is correctly set to INT. I worked my way through the troubleshooting chart and it more or less told me to replace the defective LED display. I found some good HP 5082-7740 replacements on ebay so I will start there. Would a new display completely fix the problem or should I expect another problem once the display has been replaced?


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 Post subject: Re: HP 5383a frequency counter problem
PostPosted: Sep Sat 25, 2021 3:34 pm 
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Even if you have a bad segment in one of the displays, the rest of the counter should still work and read frequencies. So if you are applying signals of reasonable amplitude and waveform, but still getting no readings, I would expect that something else is up with it.

This is a problem that can be attacked from two angles. First, you've got to make sure the applied signal is actually getting through the input attenuator and filter (which is fused, as noted above) and to the counter circuitry. An oscilloscope will be most useful here. An audio oscillator that puts out 400 Hz or 1-kHz at a volt or two makes a good signal source to troubleshoot with. (I don't like to use 60-Hz because it can get mixed up with AC line or power supply hum). Secondarily, you need to look at the reference oscillator section and make sure it is producing the right frequencies and voltages. Crystals can and do fail after long hours of service.

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 Post subject: Re: HP 5383a frequency counter problem
PostPosted: Sep Sat 25, 2021 4:46 pm 
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Right.
There is a possibility that the display board has the display driver/decoder on it and it is the reason for all zeros, in which case that would fix both problems. However I wouldn't bet on it.
Replacing the display board (if you could find one) first might be like fixing a dented fender on a car there the engine doesn't run. So I would get it to register a frequency first.
Keep in mind these service manuals are meant for the HP repair techs to use. At the time they had access to replacement boards and parts. The owner (customer) is paying the bill. To continue the automobile example, if this manual was about a car and the symptom was the engine running rough, the fix would be to replace the engine. Much simpler and quicker than tracking down the exact problem.
The 5382A and 5383A look very similar. A close look at the switches reveals differences. The 5382A input selector is all 1Mohm, no fuse. The gate time is 0.1s - MHz, 1s - KHz, 10s - Hz. With it set to MHz and no input the display shows 0.00000, but the schematic is probably somewhat different.
Attachment:
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 Post subject: Re: HP 5383a frequency counter problem
PostPosted: Sep Sat 25, 2021 11:49 pm 
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Well I checked the display board and the decoder works fine so the problem is in the main board. Its most likely that the reference oscillator might not be working correctly. Thanks Chris for the tip about the crystal, I'll check it now. I also think a counter or latch chip is bad since I get all 0's on the bus lines that go to the decoder, but that's probably how it should operate.


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 Post subject: Re: HP 5383a frequency counter problem
PostPosted: Sep Wed 29, 2021 2:25 pm 
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If you have an oscilloscope, first see if the reference oscillator is running. If so, apply a signal and trace it through with the scope.

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 Post subject: Re: HP 5383a frequency counter problem
PostPosted: Sep Wed 29, 2021 3:31 pm 
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A little digression, but this series of HP counters were interesting in their physical build. A 2 piece aluminum case you could run over with a truck and it would sustain no damage. Yet the absolute worst made front panel ever, with a laminated overlay that peeled off turning the thing an icky mustard yellow in shop/lab Marlboro country. :|

-Mark-

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 Post subject: Re: HP 5383a frequency counter problem
PostPosted: Oct Fri 01, 2021 4:01 pm 
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It seems like all the major test equipment companies tried to test the waters for lower priced equipment from time to time. HP and its succssors, Tektronix, even B&K Precision have from time to time put cost-reduced products on the market. Back in the mid-1970s relatively low cost digital frequency counters for technicians, ham radio operators, and hobbyists were like CB radios for truckers. Everybody had to have one! HP tried to tap into that market with the 5382A and 5383A which were intended to compete with lower end units. To their credit, HP reduced costs by going to a simpler case and chassis design, lightweight switches, and things like that. They did not cut back on the performance specs of the units. Those counters sold in large numbers and there are still a lot of them around.

A great many frequency counters got damaged because people would connect them directly to the outputs of CB or ham transceivers and hit "transmit," burning out the input circuitry. I've only seen one frequency counter where one of the logic chips went bad (it was an even older Heathkit) and it was an easy fix because the chips were in sockets and moving the suspect to another socket moved the problem to a different digit. I still think you need to pick one end or the other--either the input circuitry or the crystal oscillator--and go from there. One other area you can check, though less likely than an input problem, is the gate timing area. They divide the reference frequency down to get the various gate times selected by the front panel switch, which then go to a gate circuit that opens and closes. When the switch closes, the processed input frequency, which has been filtered and clipped to remove noise, is applied to the counter circuit. This is then clocked to the display and shown on the LEDs. Meanwhile the counter clears and does another count, then the display is updated. All that logical stuff should be happening as long as the power is on and you should be able to see the levels switching on the various inputs and outputs of the chips with a scope.

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