Author Topic: Repairing a 5440B/AF DC Calibrator  (Read 9200 times)

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Offline Tony_G

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Repairing a 5440B/AF DC Calibrator
« on: July 14, 2016, 07:58:16 pm »
I acquired this unit from a DoD auction where it didn't power on - It looked like it was just missing a fuse holder so I bought the calibrator and paid more than the cost of the unit to ship it to me. I now have the unit and just replaced the fuse & fuse holder.

It powers up with a fault and no display so I thought I'd start a thread on what I found - I don't have any answers yet but I'll post here as I do stuff.

The first thing I found was that there seemed to something rattling around in the unit so I took the covers off to see what it was:



Something ceramic and it seemed to just keep coming and coming out of the unit, so I took the unit apart to clean it out. I never did find out what it was so if you have suggestions shoot them across.

This is the unit with the top cover off:



The first board I removed was the Output PCA:



Then the Output/HV Control PCA:



Sample String PCA:



Preamp PCA:



DAC/Digital PCA:



DAC/Analog PCA:



Inside Regulator PCA: 



Filter Board - Both Sides:




Guard Crossing PCA:



Memory PCA:



Controller PCA



Outside Guard PCA:



Still had some crud in the unit so I opened the bottom of the 5440:



Took the front panel off:




I was looking to see if some ceramic component had just destroyed itself and this was really the only one I could find and it looks fine:



For completeness, here are some more shots:

I/O PCA:



Outside Guard Term PCA:



Front outlets



Main board:




I think I got the all the crud cleaned out - No idea what it was as I couldn't find anything that seemed to be the cause of it. I'll start cleaning up the unit, check the power supply voltages and then clean, visually inspect and reinstall each card as I go through.

Till the next time.

TonyG









Online Dr. Frank

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #1 on: July 14, 2016, 08:42:05 pm »
Hi, and welcome in the club of 544x owners..

The DAC/Digital PCA oven looks, as if it was getting too hot, judging by the color of its oven cover.
Although.. the ovens have double safety features, afair.
Open this shield, and look how it's inside.

Frank
 

Offline Tony_G

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #2 on: July 14, 2016, 08:58:21 pm »
Thanks Dr. Frank - Appreciate the welcome and tips.

When I plugged it in it just came up with nothing on the display (no zero's, no words, nothing, just dark) and the "Fault" annunciator lit. If you've seen that before, any tips on where I should look?

TonyG

Offline RobK_NL

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #3 on: July 14, 2016, 09:06:27 pm »
If both displays are dead, chances are the DC-DC converter on the display board is dead. Most likely cause is either C3 or C4 failed. Had that with two of these puppies.
Tell us what problem you want to solve, not what solution you're having problems with
 

Offline acbern

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #4 on: July 14, 2016, 11:34:48 pm »
First thing to do is to measure all internaly supply voltages. Let us know...
 

Offline Tony_G

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #5 on: July 15, 2016, 02:12:02 am »
Hi All,

I put the A19 Outside Guard Term PCA, A12 & 13 Filter PCAs, A11 Guarded XFMR Term PCA and the A17 Outside Guard Regulator PCA back into the unit so I could test power levels.

Interestingly the red LED on the A17 unit wasn't lit.

Here is what I measured - For A19 the test points are:



I measured:

Test Point   Voltage
1 +29V       40.46V
3 -29V       -40.85V
4 +5V         10.54V
5 HR+5V     10.37

Example picture:



The service manual in section 3 lists the values for the regulator test points as:



I measured:

Test Point    Voltage
2 +5.15V     5.150V
3 +5V          5.021V
4 +28V        28.000V
5 +12V        11.967V
6 -12V        -12.303
8 -5V          -5.024V

I wasn't able to find a TP7 to check on the board for the -29V - See example:



Based on this (the regulated voltages are in spec even if the power supply voltages are way off from what was on the schematic) I have to believe that the power is good.

I still can't find where that ceramic came from - Next steps will be to reinstall the other boards and then open the front panel up to see if the VFD is broken or not, check on the DC-DC convert per Rob and to take the cover off the Digital/DAC PCA per Dr Frank.

Thanks for the help.

TonyG



Offline Tony_G

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #6 on: July 15, 2016, 02:46:01 am »
I dropped all the cards into the unit with the exception of the actual front panel (the panel itself, not the front panel controller card that is attached to the main unit).

When I do this I can see the LEDs on the A16 Controller PCA light up and then extinguish one by one:



This seems to imply that the basic "guts" of the device is working - I'm going to take the front panel apart and see what is there.

Also I took the top off the DAC/Digital PCA as Dr. Frank asked - Here is what it looks like:



The board itself seems OK but I'm not sure why someone would write "console" on it (lower right corner).

TonyG

Offline Tony_G

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #7 on: July 15, 2016, 03:30:42 am »
Interesting, plugging in the A22 Display Controller causes the power supply fault LED on A17 to turn on - When I try to read any of the test points on the board I get nothing - I Looking at the schematic and with Rob's advice I'm going to check C13 & 14:



and C3 & 4:



I removed C3, C4, C13 & C14 from the circuit and measure them with my LCR meter - Crap, while I was checking them I dropped C3 & 4 and they got mixed up but they're both supposed to be 15uF/35V caps

Cap   Value      ESR
C3     3.61uF    38.0ohms
C4     11.99uF  2.34ohms
C13   0.20uF    6.92ohms
C14   45.91uF  0.24ohms

The official values are supposed to be:

C3 & 4 - 15uF
C13 - 0.22uF
C14 - 47uF

so it looks like C3 & 4 need replacing (just like Rob was suggesting) - I'll do that after dinner.

In the meantime, I'm a complete NOOB when it comes to VFDs - I have no idea if these look good or not:




Are the black marks in the corners normal?

TonyG

Offline Cubdriver

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #8 on: July 15, 2016, 04:00:32 am »
Tony -

The VFDs are basically vacuum tubes.  The black/possibly silver-ish marks in the corner are good - those are the getters.  It's a (usually) barium compound that's flashed onto the glass after the tube has been evacuated; it acts as a collector of the residual gasses that are not pumped out during manufacture.  If the vacuum seal is compromised and the display fills with air, they will turn white and flakey.

-Pat
If it jams, force it.  If it breaks, you needed a new one anyway...
 

Offline TiN

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #9 on: July 15, 2016, 04:53:13 am »
Yup, VFDs seem to be ok. Doesn't mean they aren't dim from age though, but lets hope for best.

Thanks for photos, keep them coming. Can I steal them into my T&M collection (with link to this thread).
YouTube | Metrology IRC Chat room | Live-cam | Share T&M documentation? Upload! No MB limit, firmwares, photos.
 

Offline Tony_G

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #10 on: July 15, 2016, 06:41:23 am »
Feel free to use the pictures as you'd like.

I didn't have any 15uF caps handy so I used the closest value I had, which was 10uF - No go, it still causes the regulator to light the fault LED and shutdown the power - The circuit seems simple enough that I should just have to get close with the capacitors and not exact.

Will need to look at Q1-4 and U1 next - I can pick up some caps and a replacement U1 on my way home from work tomorrow - For the purposes of testing Q1-4 should be swappable with 2N3904/6

TonyG

Online Dr. Frank

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #11 on: July 15, 2016, 06:45:13 am »
Ok, my guess was wrong, obviously, as there is no oven on this PCB.
Your unit is even older, from about  1986, so elco capacitor defects are probable
Frank
 

Offline singapol

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #12 on: July 15, 2016, 06:57:15 am »
Quote
I measured:

Test Point   Voltage
1 +29V       40.46V
3 -29V       -40.85V
4 +5V         10.54V
5 HR+5V     10.37

The vfd display requires a negative supply, as in post #5 it is -29V so I think it's missing.You need to restore this and the positive one for the display to work assuming the display controller and circuit is ok.
 

Offline Tony_G

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #13 on: July 15, 2016, 03:25:58 pm »
Thanks for the reply - According to the schematic the panel takes in 29V & 5V:



I measure 4.87V between pins 1 & 2 and 27.99V between pins 3 & 4. In fact the whole DC-DC converter doesn't take in a specific -29V line but just a 29V and 29V return:



The 6 main ICs on the board are socketed so I removed them and the problem persists. This seems to me to imply that the issue has to be in the DC-DC converter as that is really the only thing left connected to J4.

TonyG

Offline ManateeMafia

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #14 on: July 15, 2016, 04:05:03 pm »
What about CR1? Possible shorted diode in the rectifier.
 

Offline Tony_G

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #15 on: July 15, 2016, 04:29:54 pm »
Thanks for the suggestion - I checked out CR1 and it appears to work correctly (read the appropriate voltage drops and opens from the AC to the +/- pins) - I really think it has to be in U1 or one of Q1-4.

So I was just putting together a shopping list (I have to pretty much pass the store to get to work so I thought I'd drop in a grab the components regardless so they'll be on hand if needed).

The items I'm looking at are:

C3 & C4 - 15uF/35V Electrolytic Caps
U1 - LM3542N
Q1 & 2 - Fluke 272237
Q3 & 4 - 2N4403
CR 2 & 3 - TCR5315 (marked as a 2N4401 on the schematic)

In terms of replacements - I can do the following:

15uF/35V replaced with 22uF/35V (should be Ok to increase the capacitance, they don't have a 15uF electrolytic)
LM3542N replaced with a NTE1720 PWM regulator
Q3 & 4 replaced with 2N3906 PNP transistor
Q1 & 2 replaced with 2N3904 NPN transistor

The parts that I don't seem to have any information on are CR 2 & 3 - They are described as "Diode, SI, N-JFET, Current Reg, IF=5.3mA" so they must be using a JFET to protect the transistors.

I can't find anything about this part - 07910 looks like it is Teledyne Corp (Continental Devices) Hawthorne California but the closest I can come to a datasheet/more information is this page:

Military/High-Rel :  N
I(S) Nom.(A) Regulator Current :  5.2m
Z(T) Min (?) Dynamic Imped :  220k
V(L) Max. (V) limiting Voltage :  3.1
P(D) Max. (W) : 
V(P) Max.(V)Peak Oper. Voltage :  50
Semiconductor Material :  Silicon
Package Style :  TO-18
Mounting Style :  T

Any suggestions on what to use as a replacement that would be generally available? I can find several that will fit on Digikey but nothing that my local store seems to carry. I can't seem to find anything but maybe my SearchFu is just weak today...

TonyG

Offline picburner

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #16 on: July 15, 2016, 05:57:40 pm »
You must look for "Current Regulator Diodes".
I have found these but CR470 deliver 4.7mA only:
pe2bz.philpem.me.uk/pdf on typenumber/A-C/CR160.pdf
However before you replace them, test with a power supply if they generate a constant current of 5.2mA:
if they work is useless replace them....
Good luck.
 

Offline singapol

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #17 on: July 15, 2016, 06:33:28 pm »
My bad,  post#5 refers to main power supply of which +29 goes to display panel but strangely you measured
+40.46 and -40.85 respectively instead of +/-29 as stated.


Quote
I measure 4.87V between pins 1 & 2 and 27.99V between pins 3 & 4. In fact the whole DC-DC converter doesn't take in a specific -29V line but just a 29V and 29V return:

You are right this display uses +29 into DC-DC convertor to generate +41V (VCC2A) @ TP1 and +35V ( VCC2B) @ TP2 for . VCC2A for U4 - U7 and VCC 2B for U2 -U3 display drivers respectively. The +5 also
goes to the 6 SN75518 VFD drivers. Need to check if +41V and +35V are present at the display drivers.


 

Offline Tony_G

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #18 on: July 15, 2016, 07:08:53 pm »
Thanks Singapol,

The problem that I'm having with testing the DC-DC converter is that as soon as I plug in the Display Panel it puts the Regulator PCA into fault mode and that cuts off all the power so I just don't see anything on the test points.

I'm going to remove U1 when I get home because that should basically disable the rest of the DC-DC converter and let me know if the issue is in that area - i.e. plugging the display panel back in doesn't cause the regulator fault LED to light.

I also realized that I didn't include a full photo of the display panel - Here it is:



TonyG
TonyG

Offline Tony_G

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #19 on: July 16, 2016, 01:46:21 am »
Ok I'm at a bit of a loss right now.

I replaced U1, checked CR1, CR2, CR3, Q1-4 and replaced C3 & C4. Still no go - When I hook the display panel in the regulator goes into fault mode.

Took T1 out of the circuit and unplugged all the ICs - It shouldn't be pulling the supply down.

Maybe I just need to remove all the components to see if even the bare board is OK.

Thoughts?

TonyG


Offline Tony_G

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #20 on: July 16, 2016, 02:05:10 am »
And I just decided to remove absolutely everything from the DC-DC power supply:



Lo and behold! Connecting the display panel doesn't cause the regulator to fault. Now to test everything in the pile of components again....

TonyG

Offline Tony_G

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #21 on: July 16, 2016, 04:36:53 am »
Well there's your problem:



C1 is being recognized as a 0.079ohm resistor. Seeing that it is a filter cap directly across the 29v supply that would generally be regarded as "bad" by the regulator PCA.

I'm going to reinstall all the components tomorrow (late here in Seattle) and see if that lets me fire up the displays.

TonyG

Offline Vgkid

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #22 on: July 16, 2016, 05:55:10 am »
Best of luck, at least no fireworks.
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Offline singapol

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #23 on: July 16, 2016, 05:58:19 am »
Well there's your problem:



C1 is being recognized as a 0.079ohm resistor. Seeing that it is a filter cap directly across the 29v supply that would generally be regarded as "bad" by the regulator PCA.

I'm going to reinstall all the components tomorrow (late here in Seattle) and see if that lets me fire up the displays.

TonyG

Sorry I don't follow, are you testing the right pin? There are 2 supply going into SN75518  pin1 VCC2 (+41/+35) and pin40  Vcc1=+5V.  The orange tantalum reading at 79 mOhm could be correct. ( depending on capacitance value )

You replaced C3,C4 are you meaning C13 and C14?  C14 is in the +5V for pin 40.

Edit: SN75518 does not use +29V. Tantalums when new (unsoldered) can measure like what you measured.
There are different grades of tants with impedance. Try measuring a new one if you suspect it is defective which I think it is not. Afer soldering it can read higher but is expected as stated by manufacturer.
Eg. a smt 10uf tantalum states 300mOhm after soldering but before soldering it measured 78 -90 mOhm).

Are you sure NTE replacement is pin identical?
Sorry from the picture I thought you were measuing sn75518 pins when it is a tantalum after it's remove out of circuit.
« Last Edit: July 16, 2016, 06:17:43 am by singapol »
 

Offline Tony_G

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #24 on: July 16, 2016, 07:18:38 am »
Thanks Vgkid - I think the regulator PCA does a really good job of cutting the power off before anything bad can happen so I didn't see that usual burst top thing.

Sorry Singapol - I happened to be measuring the C1 capacitor and the photo was there so I thought it would make a good background.

It appears that the C1 capacitor is effectively a dead short (I wasn't showing ESR on that cap but actual resistance measurement) - When connected to the LCR meter in auto mode the meter says that it is a resistor. When I set the meter to capacitance mode it reads 'overload'. Doing the same thing with my Rigol DM3058 shows the same overload on capacitance and a slightly different but still very low resistance value. All the other tantalums measure correctly and in spec.

Based on that I believe that C1 has failed as a short and given its position in the circuit as a filter capacitor it's shorting the 29V supply.

According to the NTE 1720 Datasheet and the Fluke schematic they're identical pin outs.

I had replaced C3 & C4 with 10uF caps (which I had on hand) per Rob's suggestion that he has seen them fail - When I tested them they had indeed failed - Whether that placed undue stress on C1 and caused it to go as well or some other issue occurred I don't know. Will know more tomorrow when I put the components back in the board.

Thanks for all the feedback and help - I really appreciate everyone's willingness to help out here on the forum.

TonyG



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