Author Topic: HP 140T calibration  (Read 2390 times)

0 Members and 1 Guest are viewing this topic.

Offline Floopy

  • Regular Contributor
  • *
  • Posts: 110
  • Country: us
HP 140T calibration
« on: June 18, 2018, 11:09:03 am »
Hello,
Don't know if this is considered "repair".

I acquired an HP 140T. I ordered the plugins and they should arrive soon. In the meantime, I thought that I would make sure that the voltage rails are outputting what they should be doing.
Here are the following voltages:-12.6V, 250V, -100V, 100V, and 2350V
The last one being on a separate board labeled High Voltage for obvious reasons. I tuned the -12.6V from 11.6V to -12.601V, the 100V from 95V to 100.07V, but for some reason the 250V would only go up to 248.77V and the -100V only to -93.7V. Same for the 2350V line would only go up to 2000V. That's how far the potentiometers would go.
Is this normal? maybe it's because I don't have  the plugins installed? Do I need to fix something?

I took a picture of the low voltage board. Thankfully I had a high voltage probe on hand, although I should invest into an electricians screwdriver.

Any other concerns I should be worried about?
-Thanks
-Floopy
 

Offline Floopy

  • Regular Contributor
  • *
  • Posts: 110
  • Country: us
Re: HP 140T calibration
« Reply #1 on: June 18, 2018, 11:12:20 am »
Forgot to add:
One of the handles is cracked. Can I just take a propane torch some silver solder and fix it up?
I think I can.
-Floopy
 

Offline joeqsmith

  • Super Contributor
  • ***
  • Posts: 4828
  • Country: us
Re: HP 140T calibration
« Reply #2 on: June 18, 2018, 11:23:52 am »
A good TIG welder should be able to fix you up.   

If you have the service manuals, the should tell you how to test the voltages.  If not, the may be on-line now. 

I had the 141 with three plug-ins many years ago.   One for KHz, one for 100MHz or so and one for 1.3ish GHz.  I also had the GHz tracking generator for it.  Mine had the analog storage tube.  Have fun with it.
How electrically robust is your meter?? http://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
 

Offline Floopy

  • Regular Contributor
  • *
  • Posts: 110
  • Country: us
Re: HP 140T calibration
« Reply #3 on: June 18, 2018, 11:28:25 am »
A good TIG welder should be able to fix you up.   

If you have the service manuals, the should tell you how to test the voltages.  If not, the may be on-line now. 

 Have fun with it.
I only have a SMAW welder (Stick). I don't have access to any TIG welders anymore. I don't have the budget either.

I do have the service manual and that's the voltages it said I had to be reading. Let me double check here in a minute.

-have fun with it.
I will?
-Floopy
 

Offline Floopy

  • Regular Contributor
  • *
  • Posts: 110
  • Country: us
Re: HP 140T calibration
« Reply #4 on: June 18, 2018, 11:32:29 am »
Verified,
« Last Edit: June 18, 2018, 11:58:35 pm by Floopy »
-Floopy
 

Offline joeqsmith

  • Super Contributor
  • ***
  • Posts: 4828
  • Country: us
Re: HP 140T calibration
« Reply #5 on: June 18, 2018, 08:48:44 pm »
Welder meaning a person who is skilled in the art of welding, in this case with a TIG.  I was not suggesting you personally invest in a TIG.

That's just a table.  There should be a whole procedure for checking out the power supply. 
How electrically robust is your meter?? http://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
 

Offline Floopy

  • Regular Contributor
  • *
  • Posts: 110
  • Country: us
Re: HP 140T calibration
« Reply #6 on: June 19, 2018, 12:04:48 am »
Welder meaning a person who is skilled in the art of welding, in this case with a TIG.  I was not suggesting you personally invest in a TIG.

That's just a table.  There should be a whole procedure for checking out the power supply. 

Sorry, where I live a welder and a welder are said the same way and they mean different things. Ones a machine the other a skillful person.

I can TIG weld well enough that it doesn't look like a chicken took a dump. I also edited the previous post to include the short section about checking voltages. The manual points out where I can find the right voltages . I'm quit surprised how much documentation there is for just a service manual.

Manual:
http://bama.edebris.com/manuals/hp/140t/
-Floopy
 

Offline joeqsmith

  • Super Contributor
  • ***
  • Posts: 4828
  • Country: us
Re: HP 140T calibration
« Reply #7 on: June 19, 2018, 09:43:50 am »
Welder meaning a person who is skilled in the art of welding, in this case with a TIG.  I was not suggesting you personally invest in a TIG.

That's just a table.  There should be a whole procedure for checking out the power supply. 

Sorry, where I live a welder and a welder are said the same way and they mean different things. Ones a machine the other a skillful person.

I can TIG weld well enough that it doesn't look like a chicken took a dump. I also edited the previous post to include the short section about checking voltages. The manual points out where I can find the right voltages . I'm quit surprised how much documentation there is for just a service manual.

I only have a SMAW welder (Stick). I don't have access to any TIG welders anymore. I don't have the budget either.

You said you don't own a TIG.  Take it to someone who does and is skilled in using it. 

5-22 is preceded by 5-20 which the first sentence states "5-21. This procedure can be followed using either spectrum analyzer or oscilloscope plug-ins."   Start with 5-20 then work through it.  Jumping in the middle may not yield the correct results. 
How electrically robust is your meter?? http://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
 

Offline Floopy

  • Regular Contributor
  • *
  • Posts: 110
  • Country: us
Re: HP 140T calibration
« Reply #8 on: June 19, 2018, 03:40:30 pm »

You said you don't own a TIG.  Take it to someone who does and is skilled in using it. 

5-22 is preceded by 5-20 which the first sentence states "5-21. This procedure can be followed using either spectrum analyzer or oscilloscope plug-ins."   Start with 5-20 then work through it.  Jumping in the middle may not yield the correct results. 

-from the weight it's aluminum die cast. So TIG is the only way, unless I can find some fixing compound or something like that.  I really wish I still had access to a shop.
Anyway, according to the manual, it's the -100V supply that's throwing everything off. I just need to trace it through. I'm just afraid to plug in the modules with voltages all over the place. The manual says to test with them.
-Floopy
 

Offline kirill_ka

  • Regular Contributor
  • *
  • Posts: 107
  • Country: ru
Re: HP 140T calibration
« Reply #9 on: June 19, 2018, 09:14:44 pm »
I'm just afraid to plug in the modules with voltages all over the place. The manual says to test with them.
From my experience with 141t, you should be able to get the correct voltages without plugins.
You can try to swap power transistors to see if they are the problem.
Also take a look at Veraxis' videos:
 
The following users thanked this post: TerraHertz, Floopy

Offline Floopy

  • Regular Contributor
  • *
  • Posts: 110
  • Country: us
Re: HP 140T calibration
« Reply #10 on: June 20, 2018, 01:30:01 am »
From my experience with 141t, you should be able to get the correct voltages without plugins.
You can try to swap power transistors to see if they are the problem.
Also take a look at Veraxis' videos:
Thank you, I watched it yesterday after doing some searching. I need to find what is causing trouble on the -100V.
-Floopy
 

Offline factory

  • Regular Contributor
  • *
  • Posts: 107
  • Country: gb
Re: HP 140T calibration
« Reply #11 on: June 20, 2018, 05:59:39 am »
Firstly make sure you have the correct manual that covers the serial prefix of your 140T, they often made many changes over the years for instruments with a long production run like the 140 series.

The manual I have downloaded says all the supplies are referenced to the -100V supply (exactly like the earlier 140A's I have), but looking at the power supply diagram the adjustment pot for the +100V isn't  :-//, not sure why (there must be a mistake somewhere with the manual).

Anyway you should check all the voltages listed on the diagram for the -100V supply, to try & find out what has failed, once this supply rail is fixed you will probably find you need to re-adjust all the other rails that were referenced to this one.

For the high voltage supply, did you verify the calibration of your high voltage probe using a known lower voltage? Also the HV probe could be loading down the HV supply if it's a low ohms per volt one.

David
 

Offline factory

  • Regular Contributor
  • *
  • Posts: 107
  • Country: gb
Re: HP 140T calibration
« Reply #12 on: June 20, 2018, 06:10:36 am »
Also R473 R467 (circled in picture) looks a bit discoloured in your picture, could it be open-circuit or dry jointed? It's in part of the -100V supply.

David

edited 26/8/18 to change error.
« Last Edit: August 27, 2018, 12:11:51 am by factory »
 

Offline Floopy

  • Regular Contributor
  • *
  • Posts: 110
  • Country: us
Re: HP 140T calibration
« Reply #13 on: June 20, 2018, 06:45:36 am »
Thank you! I forgot about the little guy. I'll test them later this week when I'm not buried in other work. Also, I'm pretty sure that the manual I have is correct for the serial number. I have one of the original models. It says "last calibrated: Sept 1970". The boards are exactly the same as the ones in the pictures.

I checked the nuvistor and I didn't find any problem with it. That's how I know that the -2350V line is being affected by the -100V.

 
Also R473 (circled in picture) looks a bit discoloured in your picture, could it be open-circuit or dry jointed? It's in part of the -100V supply.
David

The symptoms are what is described here.

When I would wiggle the -100V I would get a direct response on the -2350V.

I checked the fuse voltage and they seem normal.

I just need more time to dig deeper.

« Last Edit: June 20, 2018, 06:54:17 am by Floopy »
-Floopy
 

Offline Floopy

  • Regular Contributor
  • *
  • Posts: 110
  • Country: us
Re: HP 140T calibration
« Reply #14 on: June 21, 2018, 01:59:17 am »
New question, the neon bulbs are poised to the point that they don't light anymore. I want to replace them. I only have NE2 bulbs, but the service manual says that I need NE2 and NE96.
What's the difference? Does NE96 have a different break down voltage?
-Floopy
 

Offline factory

  • Regular Contributor
  • *
  • Posts: 107
  • Country: gb
Re: HP 140T calibration
« Reply #15 on: June 21, 2018, 04:00:17 am »
New question, the neon bulbs are poised to the point that they don't light anymore. I want to replace them. I only have NE2 bulbs, but the service manual says that I need NE2 and NE96.
What's the difference? Does NE96 have a different break down voltage?

Those neons NE2 (V606) & NE96 (V607, V608) are between the grid & cathode of the nuvistor & CRT, they will only light when the grid to cathode voltage is too high, usually I've only seen them only light during power up before the tube heaters have warmed up, do yours light briefly at power up?
The NE96 has a higher breakdown voltage than the NE2.
Also be very careful not to disturb them as the legs are made from copper plated steel, they tend to either snap off or fall off very easily if knocked, I even found one in the bottom of a parcel from a 140A scope I bought years ago (that was a very easy fix, it had stopped the timebase from running).

I still think you should concentrate your fault finding with the -100V supply before worrying about the HV section.

David
« Last Edit: June 21, 2018, 04:04:18 am by factory »
 
The following users thanked this post: Floopy

Offline Floopy

  • Regular Contributor
  • *
  • Posts: 110
  • Country: us
Re: HP 140T calibration
« Reply #16 on: June 21, 2018, 11:50:18 am »
New question, the neon bulbs are poised to the point that they don't light anymore. I want to replace them. I only have NE2 bulbs, but the service manual says that I need NE2 and NE96.
What's the difference? Does NE96 have a different break down voltage?

Those neons NE2 (V606) & NE96 (V607, V608) are between the grid & cathode of the nuvistor & CRT, they will only light when the grid to cathode voltage is too high, usually I've only seen them only light during power up before the tube heaters have warmed up, do yours light briefly at power up?
The NE96 has a higher breakdown voltage than the NE2.
Also be very careful not to disturb them as the legs are made from copper plated steel, they tend to either snap off or fall off very easily if knocked, I even found one in the bottom of a parcel from a 140A scope I bought years ago (that was a very easy fix, it had stopped the timebase from running).

I still think you should concentrate your fault finding with the -100V supply before worrying about the HV section.

David

Your right, they do light just before the CRT begins to light up. I thought that they where dead. I plugged in the modules to see if it would change the voltage in anyway and it didn't. I ended up blowing the fuses on the modules also. At least I verified that they worked. I've tested the  power transistors and they are okay. I swapped them and the voltage is exactly the same.

I measured the reference voltages that are given on the schematic. The ones outlined in blue mean they are different, the ones with a green check mark mean they are withing 0.2V of the marked voltage. I measured by touching the ground plane with the negative probe and the positive probe went where I was measuring. For some reason I forgot to write down the voltage I had for terminal 927. I will update it when I open it again. The markings of the side of the paper is the resistors that are heating up and discoloring the board. I'm really starting to get stumped on what might be producing the problem. Probably because I haven't worked as much with these kind of power supplies before.

Sorry for all my mistakes, this is the first time I trouble shoot such a large and dangerous piece of equipment.

EDIT: the One I forgot to write down (29V next to power transistor), is 62V+. That is not normal and I'm pretty sure I measured that right.
« Last Edit: June 21, 2018, 11:56:33 am by Floopy »
-Floopy
 

Offline Floopy

  • Regular Contributor
  • *
  • Posts: 110
  • Country: us
Re: HP 140T calibration
« Reply #17 on: June 22, 2018, 02:26:27 am »
I merged the two schematics in the service manual since they where overlapping.
-Floopy
 

Offline factory

  • Regular Contributor
  • *
  • Posts: 107
  • Country: gb
Re: HP 140T calibration
« Reply #18 on: June 22, 2018, 06:23:37 am »

Your right, they do light just before the CRT begins to light up. I thought that they where dead. I plugged in the modules to see if it would change the voltage in anyway and it didn't. I ended up blowing the fuses on the modules also. At least I verified that they worked. I've tested the  power transistors and they are okay. I swapped them and the voltage is exactly the same.

I measured the reference voltages that are given on the schematic. The ones outlined in blue mean they are different, the ones with a green check mark mean they are withing 0.2V of the marked voltage. I measured by touching the ground plane with the negative probe and the positive probe went where I was measuring. For some reason I forgot to write down the voltage I had for terminal 927. I will update it when I open it again. The markings of the side of the paper is the resistors that are heating up and discoloring the board. I'm really starting to get stumped on what might be producing the problem. Probably because I haven't worked as much with these kind of power supplies before.

Sorry for all my mistakes, this is the first time I trouble shoot such a large and dangerous piece of equipment.

EDIT: the One I forgot to write down (29V next to power transistor), is 62V+. That is not normal and I'm pretty sure I measured that right.

Ok your measured voltages for Q462 are;
Collector 62V
Base 1.2V
Emitter 0.5V

As you have checked the series regulator (power) transistor is OK, I suspect Q462 is open circuit, you should be able to verify this out of circuit with the diode check on your DMM.
As usual the manual only gives a HP in-house part number for it (1854-0022), it's probably a standard part but it will need looking up in the equivalent charts available on the web.

I don't think you need to worry too much about resistors R467 & R473 (the discoloured ones) as they form a voltage divider across the +100V & -100V rails and the -20V is correct. You may wish to re-solder them if the joints look dry and if I've done my calculations correctly they only dissipate about 0.8W of heat between them.

David
« Last Edit: June 22, 2018, 06:26:44 am by factory »
 
The following users thanked this post: Floopy

Offline Floopy

  • Regular Contributor
  • *
  • Posts: 110
  • Country: us
Re: HP 140T calibration
« Reply #19 on: June 24, 2018, 02:11:57 am »
As you have checked the series regulator (power) transistor is OK, I suspect Q462 is open circuit, you should be able to verify this out of circuit with the diode check on your DMM.
As usual the manual only gives a HP in-house part number for it (1854-0022), it's probably a standard part but it will need looking up in the equivalent charts available on the web.

I de-soldered and it tested fine, NPN no shorts. Should I try replacing it anyway? I don't see who else could be causing problems. It seems that the wrong voltage is being applied to the base of the regulator and its' raising the voltage from 29V to 62V. I'm going to do a little more probing around and trace the voltage as it goes through. I'll test the reference voltages on the +100V and see if everything is normal.

Thanks!
-Floopy
 

Offline factory

  • Regular Contributor
  • *
  • Posts: 107
  • Country: gb
Re: HP 140T calibration
« Reply #20 on: June 24, 2018, 05:54:14 am »

I de-soldered and it tested fine, NPN no shorts. Should I try replacing it anyway?


It won't be shorted as all the voltages measured for that transistor were different, but was either half of it open circuit? The only other part that could potently be open circuit is R465 (56k).

David
 

Offline Floopy

  • Regular Contributor
  • *
  • Posts: 110
  • Country: us
Re: HP 140T calibration
« Reply #21 on: June 24, 2018, 11:50:30 am »
I de-soldered both 1854-0022 transistors, (there where two) and swapped places. The outputs where almost exactly the same. I tested the 56K resistor and it was reading fine. The only voltage differences in the 100V+ circuit was the zener (CR445) was at 52.8V instead of 69.8V and the inputs at terminal 926 was 154V instead of 126V. I measured the "calibrator" voltage and it was extremely off the page. it was reading -0.5V instead of 1V and -4.5V instead of 10V. I tested the transistor and it had a base to emitter of 0.2. I un-soldered it and disconnected the resistor that was connecting to -100V (R493). No luck unfortunately, the output was just the same. I just need to dig deeper, I'm going to start trying to disconnect certain parts of the circuits and other boards to see what happens.
-Floopy
 

Offline factory

  • Regular Contributor
  • *
  • Posts: 107
  • Country: gb
Re: HP 140T calibration
« Reply #22 on: June 24, 2018, 10:58:54 pm »
Unless there is a track break or bad connection in that area I'm not sure what else to suggest, I've had a quick look at the pictures of the power supply boards in mine, none of the adjustment pots are at the end stops, do they all actually change the output voltages when adjusted?
The discoloured board around the resistors, mentioned earlier may indicate your 140T has had a lot of use, none of mine are like that.

Also one of the manuals (140A 1967) mentions that the measured voltages on the circuit diagrams may vary depending on the plug-ins fitted, of course with no load (no plug-ins) that may explain the higher voltages before the regulator transistors.

As for the calibrator, the outputs are a 1V & 10V peak to peak square wave at mains input frequency (i.e. 50Hz or 60Hz depending on country), did you use an oscilloscope to check this?
The transistor Q490 is germanium type, they have a lower forward voltage than silicon types, but if it's reading 0.2V (base to emitter) both ways (out of circuit) then it's leaky.
One important thing with the calibrator circuit, DO NOT measure the tunnel diode (CR490) with your DMM as they are very easy to destroy, they can also be damaged very easily with the heat of soldering.

David
 

Offline Floopy

  • Regular Contributor
  • *
  • Posts: 110
  • Country: us
Re: HP 140T calibration
« Reply #23 on: June 25, 2018, 02:30:12 pm »
Well, never thought I would end up doing this.
I ended up taking almost everything apart. Finally I had enough and I thought that if the potentiometer won't go farther, I will make it go farther. R470 is a resistor that is right before the regulating potentiometer. It's value is only 4320 \$\Omega\$, I grabbed a similar resistor that was 5.9K and swapped the two. I could now regulate it to where I wanted it and I got all the other lines to where they needed to be. No problem anywhere. I plugged in the units and the fuses have not been blowing anymore (crossing fingers). I forgot to mention that they where blowing. I did not find anything odd after some testing. Is this a band-aid, or a real solution? I think it's fine now.

Also the fan was not turning very fast at all. (maybe 2 RPM). Taking it out was a pain! Really! I oiled the shaft after a disassembly and now it's blowing enough air that I can feel it on the side vents.

Anything else I should look for. Right now it looks really nice with everything setup
-Floopy
 

Offline Floopy

  • Regular Contributor
  • *
  • Posts: 110
  • Country: us
Re: HP 140T calibration
« Reply #24 on: June 26, 2018, 03:49:20 am »
Forgot to mention. I measured the 1V and the 10V, I didn't know it was a peak-to-peak voltage. It measured fine, the problem was my ignorance.
-Floopy
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf