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Old 22nd Oct 2018, 7:06 pm   #1
Kopferkingel
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Default HP 180A Oscilloscope - reviving and resurrection

I got the scope in a rather nice visual shape and I would certainly like to get it reasonably working. So far I´ve done the cleaning and basic measurements. The power supply seems to be working just fine. All voltages seem to match the specifications, which is quite impressive for such an old machine. But - there is no trace. The HV regulator circuit seems to have some decent voltage, but the oscillator transistor remains cold and there is no HV nor screen activity. I am not getting any voltage measurements on the transistor (which I´m having some troubles identifying). There is a fuse underneath which is fine and measures 30V on both ends against ground (?). I´ve also tested the other fuses on the bottom - all OK. This is rather puzzling and frustrating at the same time.

I´d like to get more information on general failures of these machines or some tips or tricks where to eventually look You know - source of inspiration, since my primary objects of interest are reel to reel recorders and VCR´s. Thanks very much in advance.


P.S: I´ve searched and I am aware of the resistor failures of some HP machines but I´m not sure if this is the case.
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Old 22nd Oct 2018, 8:30 pm   #2
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Default Re: HP 180A Oscilloscope - reviving and resurrection

The marking on that transistor is the shortened version of an HP stock number. It looks like 4-291

so the full version will be 1854-0291

1854 means silicon bipolar NPN. 0291 is just a chronologically issued number that doesn't encode any other meaning

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Old 22nd Oct 2018, 8:42 pm   #3
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Default Re: HP 180A Oscilloscope - reviving and resurrection

Thanks for the clue. Well, there is something to begin with. Now for the tricky part: Finding out why there is no power to it at all. I tried measuring all three pins against ground, just to be sure. The outcome is just 0 which puzzles me.
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Old 22nd Oct 2018, 8:47 pm   #4
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Unhappy Re: HP 180A Oscilloscope - reviving and resurrection

I owned an HP180A many years ago, (1982 or thereabouts ), but one day it failed in same way yours has. Eventually I was forced to accept that the HV transformer had failed. The only source for a replacement - a complete HV ass'y - was from HP. But the cost (incl. shipping) was well into £ three-figures. That rendered it B.E.R., sadly.

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Old 22nd Oct 2018, 9:38 pm   #5
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Default Re: HP 180A Oscilloscope - reviving and resurrection

Oh, yes. thought of the faulty HV transformer as well, but wouldn´t the oscillator still be working? There isn´t even a blown fuse. The bad thing is that the rear side of the scope is a nest of wires. I find it rather hard to disassemble carefully. Too bad I come from a country where HP scopes are rather exotic. It might be quite hard to obtain an "organ donor"
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Old 23rd Oct 2018, 12:13 am   #6
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Arrow Re: HP 180A Oscilloscope - reviving and resurrection

"Wouldn't the oscillator still be working?" you ask. It's been a very long time since I had the aforementioned trouble with the HP 180A that I had, but I think I discovered that the oscillator needed a coupling winding from the HV transformer. If that transformer has developed shorted turns, (quite likely, IMHO), it will place a substantial load on its driver transistor and also severely damp any coupling winding to the oscillator. Net result is, of course, no osc. & no HV.

At the end of the day, everything here depends on two things: What your need is and how much cash you are prepared to spend. I used to use two Tek. 475 'scopes, but as the years went by, I had so much trouble constantly trying to fix them that in the end I gave up - and bought a 2nd. hand Tek. 2465 for £300. I've had it for 5 years now. It's vastly superior to the 475 in performance and still working O.K. (Tempts fate yet again! )

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Old 23rd Oct 2018, 5:25 am   #7
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Default Re: HP 180A Oscilloscope - reviving and resurrection

"Oh, yes. thought of the faulty HV transformer as well, but wouldn´t the oscillator still be working?" No. From a quick look the oscillator runs off the +15v rail, you also have +/-100v and +12.5v, if you haven't got those nothing else will work. Manual here - http://bee.mif.pg.gda.pl/ciasteczkowypotwor/HP/180A.pdf

Andy.
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Old 23rd Oct 2018, 5:52 am   #8
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Default Re: HP 180A Oscilloscope - reviving and resurrection

But I´ve got them. All the voltages are there The power supply seems to work just fine. This is what bothers me. Yet, there is no voltager measurable on the oscillator. Strange.
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Old 23rd Oct 2018, 3:54 pm   #9
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Default Re: HP 180A Oscilloscope - reviving and resurrection

The regulator stage of the HV-generator indeed works from the stabilized voltages, +15V, +/-100V, but the power transistor itself is fed from the unregulated +23V, through a 0.5A fuse. You might want to check that out too.

Good luck, Peter
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Old 23rd Oct 2018, 5:38 pm   #10
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Default Re: HP 180A Oscilloscope - reviving and resurrection

The power transistor tests OK, The feeding voltage looks good as well. This thing certainly requires a trained TV technician
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Old 24th Oct 2018, 12:24 am   #11
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Arrow Re: HP 180A Oscilloscope - reviving and resurrection

You are correct! At this point in the diagnosis, a trained T.V. tech. would substitute a 'known good' HV transformer. Regretfully, it seems that that option is not available to you.
But I wonder what your chances might be of finding a scrap HP180A on e-bay? Even if its 'one day' . . . .

Al.
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Old 24th Oct 2018, 5:42 am   #12
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Default Re: HP 180A Oscilloscope - reviving and resurrection

The chances are slim. There are some spare parts available right now. There is even a guy from Germany selling the "monitor assy" with a good potential but the prices are out of this world. 50 Euro/piece + 50 Euro shipping. No way!
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Old 24th Oct 2018, 5:55 am   #13
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Default Re: HP 180A Oscilloscope - reviving and resurrection

So you should have about +22v on the oscillator's power transistor collector. 0v on the emitter and about 0.7v DC bias inn the base.... if the circuit is not oscillating due to a short on the transformer.

Note the two diodes at the transistor base. one in series and one backwards across base-emitter. These are to protect the transistor from reverse base-emitter voltage from the transformer. Check them. They need to be quite fast types. Everyone on this forum seems to put 1N4007 diodes everywhere but they are much too slow here and will slowly kill the power transistor. Don't even try one.

If you haven't got the right DC bias. then fix that first.

If you have got the right DC bias, but no oscillation, then it looks like something is shorting the transformer. The transformers are normally reliable, so there is a chance it might not be an internal short. So the next step is to check the things on the secondaries. A failed high voltage diode or capacitor or a fault in the tripler will stop the oscillator.

Be careful, because the circuit has a lot of output voltage capability and needs the feedback system to govern it. Run without the feedback regulator working, it can produce increasing voltage until something breaks down and fails. This may have already happened and is why there is a fuse in the +22v feed.

One safer way to test would be to disconnect the primary of the transformer and drive it with an audio signal generator at about 25kHz and then go looking at the secondary voltages as you increase the voltage from the audio generator.

I have an HP EHT unit in the attic, but it came from a microwave link analyser which means it's an earlier generation, the MLA used the rectangular CRT of the later generation 140A scope. I gave away all my HP180A stuff two years ago (3 scopes, one donor and even the spectrum analyser plug-in)

The later 1740A scope uses the same CRT as the 180A so a transformer from one of those might work, but the only ones I have are all in working scopes.

David
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Old 24th Oct 2018, 6:28 am   #14
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Default Re: HP 180A Oscilloscope - reviving and resurrection

"But I've got them. All the voltages are there" That's good, so the main transformer is ok. Don't despair, these are pretty simple scopes.

As David said he gave away his 180A's, I've got two, one for spares. If you need a replacement part I might be able to help, but check as advised first.

Andy.
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Old 24th Oct 2018, 12:00 pm   #15
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Default Re: HP 180A Oscilloscope - reviving and resurrection

Hi!

Is this any use?

https://www.ebay.co.uk/itm/HP-182T-O...kAAOSwvNlbWeJK

The seller may post to the C.R. if you contact him and ask for a postage price!

(Link mentioned under Forum eBay rule exception as this is the same component/section in similar equipment as the OP is dealing with!

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Old 24th Oct 2018, 12:35 pm   #16
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Default Re: HP 180A Oscilloscope - reviving and resurrection

HP180A
I would be cautious over using the EHT transformer from a model 182T, which is the large screen model, with slightly different voltages from the HP180. Particularly at the price quoted.
You have an offer of an HP180 transformer. I might be able to find you one as well.
The HP180 has a particularly good tube, fine and bright, better to my mind than the comparable Tek of that period. So worth getting going.
You will need a stock of low current fuses. This model uses fuses instead of current limiting, and fuses seem to blow readily when fault finding. Keep checking them.
The HP1740 transformer has a different part number, but it looks identical electically, as David RadioWrangler says.
Thanks for his warning about the fast switching diodes.
The oscillator transistor 1854-0291 is selected. The one in the HP1740 is 1854-0433, quoted as 90W, Ft 2Mhz, so a 2N3055, TIP33C should be useable for a substitution trial.
The manual you are directed to is a poor copy.
But the HP Archive itself does not offer a copy. Amazing for one of their best sellers of the early 1970's.
I have the manuals for the HP180A, 180C and 182, including most later modifications. And also most of the plug-in units - also not many on the Archive. I can scan them if you are stuck.
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Old 24th Oct 2018, 3:19 pm   #17
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Default Re: HP 180A Oscilloscope - reviving and resurrection

I have good readable pdf of the HP180C & D service manual if wanted to save Bill some scanning. It's 6.5MB large.
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Old 24th Oct 2018, 4:30 pm   #18
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Default Re: HP 180A Oscilloscope - reviving and resurrection

1854-0291 has ft of 1M @ 2 amps and hfe between 18 and 55 at 3 amps, and Ic max 3 amps.

Peter
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Old 27th Oct 2018, 9:08 pm   #19
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Default Re: HP 180A Oscilloscope - reviving and resurrection

So, I´ve done a little bit of poking around. The oscillator transistor as well as the litle board containing 2 capacitors, inductor and diode seems to be OK as well. I´ve also checked the resistance of both primary windings of the HV transformer. They are 1 ohm and 1,3 ohms. I don´t know whether this is a normal value but given the circumstances I am not alerted about that. As for the spare parts - yes, some of them are on Ebay. I managed to find the whole NOS HV regulator board but I´ll be absolutely honest - the prices are out of this world for me. We are talking about 35 £ + 30 £ shipping or so. This is a considerable amout of money for us here in CR. Not complaining, just saying.

Another thing - I would be very grateful if anybody has a good copy of the schematics since I´m unable to decipher the values for some of the transistors on the HV regulator board, especially the Q303 and the VR302 diode. I´m still scratching my head about this part,
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Old 27th Oct 2018, 9:49 pm   #20
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Default Re: HP 180A Oscilloscope - reviving and resurrection

here you go, freshly scanned, colour and greyscale
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