UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Test Gear and Workshop Equipment

Notices

Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders.

Reply
 
Thread Tools
Old 1st Aug 2021, 9:53 pm   #81
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 18,214
Default Re: HP 180A Oscilloscope.

Note that the trace selector knob on the 1801A has positions to select which channel is used for trigger when two channels are displayed. It's easy to get this wrong and input the signal to the channel the trigger isn'r watching.

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is offline   Reply With Quote
Old 2nd Aug 2021, 8:46 pm   #82
factory
Heptode
 
Join Date: Jul 2009
Location: Cheshire, UK.
Posts: 962
Default Re: HP 180A Oscilloscope.

Thanks will double check that, as I see I forgot to connect the other channel in the last picture.

If that's not the problem, then it's back to checking the sync amplifier board (A6) on the 1801A, there are eight waveforms given on the circuit diagram pages, it uses the 180A 10Vpk cal output for these checks.

David

Last edited by factory; 2nd Aug 2021 at 8:51 pm.
factory is offline   Reply With Quote
Old 8th Aug 2021, 8:53 pm   #83
factory
Heptode
 
Join Date: Jul 2009
Location: Cheshire, UK.
Posts: 962
Default Re: HP 180A Oscilloscope.

Quick update on the trigger problem with my 1801A & 1821A plug-ins.
Will do a more detailed post another night, but the problem wasn't the trace selector control, it was a failed transistor in the 1801A sync amplifier board.

It's now working OK using both internal timebase triggers.
Click image for larger version

Name:	DSC_4888a.jpg
Views:	29
Size:	81.2 KB
ID:	239106 Click image for larger version

Name:	DSC_4891a.jpg
Views:	29
Size:	92.8 KB
ID:	239105

David
factory is offline   Reply With Quote
Old 8th Aug 2021, 9:34 pm   #84
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 18,214
Default Re: HP 180A Oscilloscope.

With the centremost knob of the time/division stack fully anticlockwise ('main') this is the normal single-timebase setting..... but, if you bring the delayed timebase time/division (outermost ring of that stack) back out of the 'off' position, then the delayed timebase is anabled and will run (if it is triggered) and it will bright up the traces during its run time.

So you can see just when in the waveform you are studying, the fast (delayed) timebase will expand to fill the screen. Move the 10-turn delay pot and the delayed timebase time/div, to get the bright up over the feature you want to look at in detail. Select 'delayed' on the centre knob and this is what you get.

The bright-up mode is great for fiddling with the trigger of the delayed timebase if you need to use it. You get to see what you will get, in the context of the full waveform.

Slow trigger is optimised for trad TV field rates or slower, fast trigger is optimised for trad TV line rates or faster

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is offline   Reply With Quote
Old 14th Aug 2021, 2:31 am   #85
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 18,214
Default Re: HP 180A Oscilloscope.

Re the screw holes for the mumetal screen...

The mumetal screens were brought in from the US. The bent aluminium parts of the chassis will have been made downstairs in phase-1, the only building of the time, in Jim Peachey's machine shop. I expect the parts would have been pressed on hard tooling made locally in the toolroom, to drawings from the US.

It might be a local error, or sometimes we ran into drawing errors where two parts were supposed to match/mate but didn't and an informal fix in the US was discovered not to have caused a proper fix of the wrong drawing.

On mentioning the toolroom, there is a very long article on the HP memories site by John Wastle which starts with his education, a period at Ferranti and then his move to HP's tool room and his progress up the firm. It makes fascinating reading, dishes some dirt on several managers at all sorts of levels (names changed to protect the guilty...). It's compelling reading for anyone with knowledge of the firm. Those incidents and individuals in it where I've got direct knowledge match his descriptions. The HP memories custodians didn't dare edit it! It tells the tale of sub-empires battling each other within the empire of a fortune 500 company, of personal fiefdoms. It gets messy. John wasn't 100% innocent, he was fighting for his empire, too. We in R&D/manufacturing of a division just wanted to get products designed and selling. It felt like we were fighting procurement sometimes in the later years.

I'm inclined to believe John, and I can decode plenty of the changed names.

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is offline   Reply With Quote
Old 26th Aug 2021, 2:02 pm   #86
factory
Heptode
 
Join Date: Jul 2009
Location: Cheshire, UK.
Posts: 962
Default Re: HP 180A Oscilloscope.

Quote:
Originally Posted by factory View Post
Quick update on the trigger problem with my 1801A & 1821A plug-ins.
Will do a more detailed post another night, but the problem wasn't the trace selector control, it was a failed transistor in the 1801A sync amplifier board.

It's now working OK using both internal timebase triggers.
Attachment 239106 Attachment 239105

David
Forgot to update this.

To prove whether the internal trigger problem was in the 1821A timebase or 1801A vertical input, I used the other pair of plug-ins (1824A & 1801A), swapping the 1821A timebase for the 1824A, it was still not triggering properly unless a very large trace was present.
And using the other 1801A (only one channel works at the moment) with the 1821A, it was triggering fine. That proved the trigger problem was with the original 1801A plug-in (it wasn't an incorrect trigger selection either).

Looking at the diagrams, the internal trigger signal comes from the sync amplifier circuit in the 1801A vertical plug-in.
Click image for larger version

Name:	DSC_4852a.jpg
Views:	10
Size:	60.1 KB
ID:	240133 Click image for larger version

Name:	DSC_4856a.jpg
Views:	13
Size:	51.6 KB
ID:	240134 Click image for larger version

Name:	DSC_4742b.jpg
Views:	13
Size:	67.7 KB
ID:	240135

After setting up the switches & inputs as shown on the diagram page and going though the sync amplifier circuit test points, it was found that the signal got reduced to almost nothing after Q714, instead of being amplified (note: readout incorrect as non-Tek 10x probes were used).
Click image for larger version

Name:	DSC_4855a.jpg
Views:	10
Size:	60.2 KB
ID:	240136 Click image for larger version

Name:	DSC_4846a.jpg
Views:	11
Size:	48.3 KB
ID:	240137

Before pulling Q714, I verified the -10V supply rail from that big rusty gold plated Zener was present & correct, it was OK. Then I removed Q714 and found base/emitter was open circuit, it was marked MPS3563 (listed as 1854-0092 in the manual), I didn't have any MPS3563 or 2N3563, but a bit of searching found a donor board with some 4-092 (aka 1854-0092).

After replacing Q714 the internal trigger function was once again working , pictures are in the quoted post.

David
factory is offline   Reply With Quote
Old 26th Aug 2021, 3:26 pm   #87
factory
Heptode
 
Join Date: Jul 2009
Location: Cheshire, UK.
Posts: 962
Default Re: HP 180A Oscilloscope.

Quote:
Originally Posted by Radio Wrangler View Post
With the centremost knob of the time/division stack fully anticlockwise ('main') this is the normal single-timebase setting..... but, if you bring the delayed timebase time/division (outermost ring of that stack) back out of the 'off' position, then the delayed timebase is anabled and will run (if it is triggered) and it will bright up the traces during its run time.

So you can see just when in the waveform you are studying, the fast (delayed) timebase will expand to fill the screen. Move the 10-turn delay pot and the delayed timebase time/div, to get the bright up over the feature you want to look at in detail. Select 'delayed' on the centre knob and this is what you get.

The bright-up mode is great for fiddling with the trigger of the delayed timebase if you need to use it. You get to see what you will get, in the context of the full waveform.

Slow trigger is optimised for trad TV field rates or slower, fast trigger is optimised for trad TV line rates or faster

David
I've never used a scope for looking at TV signals, will have to do give it a try as I have various scopes that have TV trigger modes, also should try the 180A too.

All the sweep modes were checked, just didn't post pictures of them as it was quite late at night when I added that quick post, after fixing the trigger problem.

For future reference for anyone else repairing vintage hp 180 series scopes & others, here are some pictures of the different sweep modes with the 1821A timebase.

Main sweep, red control set to Main sweep and outer delayed sweep to a faster sweep, than the middle main sweep control, these are all part the triple Time/CM control. The CM Delay gives an intensified section on the trace when triggered, which increases the more the ten turn control is increased.
Click image for larger version

Name:	Main sweep.jpg
Views:	17
Size:	79.9 KB
ID:	240140

Mixed sweep, red control set to Mixed sweep and other controls are unchanged, this shows both the normal sweep and the delayed sweep.
Click image for larger version

Name:	Mixed Sweep.jpg
Views:	18
Size:	80.4 KB
ID:	240141

Delayed sweep, red control set to Delayed sweep, other controls unchanged, this only shows the faster delayed sweep portion of the above mixed sweep mode.
Click image for larger version

Name:	Delayed Sweep.jpg
Views:	17
Size:	74.6 KB
ID:	240142

Something I noticed when checking all the modes out, is that the light behind the reset switch was never lit, even when set to single sweep. In fact I've only ever seen it lit briefly at power up. The 1821A manual doesn't seem to mention it outside of the single sweep mode.

But comparing the 1821A timebase with the older 1421A timebase, which shares some circuitry in this area, it seems to light when a triggered sweep is running and goes out briefly at the start of the sweep.

David
factory is offline   Reply With Quote
Old 26th Aug 2021, 3:42 pm   #88
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 18,214
Default Re: HP 180A Oscilloscope.

The light in the reset button is a neon.... it might be getting too low emission or too high a strike voltage to light properly.

Congratulations, you now have a nice scope. Because of the HP badge, no-one will believe you ever got it triggering

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is offline   Reply With Quote
Old 26th Aug 2021, 4:21 pm   #89
factory
Heptode
 
Join Date: Jul 2009
Location: Cheshire, UK.
Posts: 962
Default Re: HP 180A Oscilloscope.

The high striking voltage of the aged neon must be the problem here, as it lights briefly at power-up, maybe the voltage is just high enough before the PSU starts regulating, but I haven't checked this.

Yesterday I had a look at the switch & neon problem, first I noted for the single sweep mode the switch had to be pressed quite hard to get the neon on the circuit board to light.

As for neon in that switch, well it's part of the Schmitt trigger circuit on the main sweep circuit diagram.
As before I set the controls & input as listed opposite the circuit diagram page and went through checking the waveforms at the test points (I've added the missing text using a 1820A manual as a reference ), nothing seemed to be wrong with any of them.
Click image for larger version

Name:	DSC_5283a.jpg
Views:	10
Size:	56.4 KB
ID:	240156 Click image for larger version

Name:	DSC_5285a.jpg
Views:	11
Size:	57.0 KB
ID:	240157

Then I checked what was happening at the collector of Q203, again I was getting something that looked OK (no waveform shown in the manual), I pulled a couple of the resistors in the chain to check they had not drifted and they were all OK.
That only left the neon lamp in the switch, to check this I found one from another 1821A (that has been a parts donor for various repairs) and temporarily connected it across resistor R215. It was working fine and this proved the original was knackered.
Click image for larger version

Name:	DSC_5277a.jpg
Views:	9
Size:	118.4 KB
ID:	240158 Click image for larger version

Name:	DSC_5279a.jpg
Views:	10
Size:	90.1 KB
ID:	240160

The switch with neon isn't the easiest part to replace, but probably not the most difficult either. Once the dozen or so screws were removed, along with the side panel, it wasn't too hard to replace, note the wire colours have faded a bit in this 1821A.
Click image for larger version

Name:	DSC_5281a.jpg
Views:	13
Size:	130.9 KB
ID:	240159
The replacement switch seems to be in better condition too, as it requires less force to operate in single sweep mode.

That's two vintage hp scopes here that work & trigger , I currently only have this 180A & the 140A here (others are in storage) I had to bring back the other 1421A plug-in from storage to prove the operation of the reset neon, the 1421A I already had here failed last weekend, the sweep length gradually reduced and stopped working.

David
factory is offline   Reply With Quote
Reply

Thread Tools



All times are GMT. The time now is 9:17 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Copyright ©2002 - 2021, Paul Stenning.