Fluke 5440A repair

[MegaVolt]

I received a Fluke 5440A in excellent condition with a small error. I thought it would be easy. But I checked everything I could and I don't see a problem: (I will accept any hints

This is what I see. When turned on, all the dots on the screen light up except for one position where the "?" This is problem?

Then I see an inscription (DV instead of DC)
5440A DV CALIBRATOR
FRONT PANEL RUNNING

And after the error "FRONT COMMUNIC FAULT"

In the service manual, this is error 64. Loss of communication between A2 and A16. But I switched the device to test mode and with the oscilloscope I see an exchange between these two boards in both directions. Signals are similar to RS232. This means that the UART is working, the processors are working, the communication line and buffers are working. I checked the frequencies they are normal.

What else can you check ??

Firmware except MC68701 I could not read it.

[picburner]

The first thing to check is if all the voltages are right and if the ripple of each is within the tolerances shown in the service manual.
A strong ripple on 5VDC could disturb the communications between the main cpu and the front panel as well as create other anomalies.
I have a 5440B which differs in the display (VFD vs LCD) and other little things.

[MegaVolt]

The first thing to check is if all the voltages

Thanks for your participation.

I have checked the voltages related to the processor boards. Everything is fine. The connection is made by differential signals of 5V swing each. This is a very reliable communication channel )

But I didn't check the rest of the voltages. Perhaps it makes sense to do everything.

I thought that someone has information on how the ping is done. Or perhaps it has waveforms.

[TiN]

Check for life on main processorboard, check reset lines, check XO outputs, check if firmware chips on all digitaly boards is good or not. 

[MegaVolt]

Check for life on main processorboard, check reset lines, check XO outputs, check if firmware chips on all digitaly boards is good or not. 

Thank you Ilya for your participation

1. The files that I posted are read from the current boards. Unfortunately, I cannot find out how much the correct firmware is in them.
2. Processors work and send information via UART. This means that some of the firmware, reset, and generator are working.

I see that the boards are working, displaying information on the screen and trying to communicate with each other. But something is not going quite the way it should be.

Perhaps the firmware began to be erased and a couple of bits changed their meaning: (((I'm trying to find another firmware to compare. But it's difficult I found only one person on the Internet with a similar device

[picburner]

The communication from A16 and A2A1front panel is by RS-422 data link @ 65KBaud.
The firmware on eproms (on A16) is protected by checksum, if it starts to lose bits it should make an error during boot.
At least this is written in the 5440A service manual.

[MegaVolt]

At least this is written in the 5440A service manual.

Thank you for this valuable information.  You can share the service manual for model "A".  I didn't find it.  there is only for "B".

[MegaVolt]

https://youtu.be/RgqR6af6lQc

Added a video in which the LEDs are visible.  It looks like the code is fine.  But there is a constant restart and there is an FPC error.  The LEDs in the distance are 4 diagnostic LEDs.  LED near it is Fault.

[picburner]

Yes, there is a fault: the four LEDs must all turn off to successfully complete the test (and remain off...).
I got this service manual here

[MegaVolt]

Maybe someone has copies of memory chips from 5440A?

[velik_kazakov]

Maybe someone has copies of memory chips from 5440A?

Hi, I get your post. I send it (not sure that all is is the zip, but front controller is in).

[MegaVolt]

Hi, I get your post. I send it (not sure that all is is the zip, but front controller is in).

Thank you so much! This is a big relief
100% match ))

I have to start thinking differently to understand the cause of this error.

I can definitely see the byte coming to the front panel and see the panel's response back. These transfers follow periodically.

Studying the A16 is difficult until I have extension cables (on the way).

[velik_kazakov]

The symbols on the LCD is generated from decoder and ROM. I don't remember now , but if I find some time in next days will check the schematic. Maybe you can to find the error on the decoder for this symbol. Just that is in my memories. Because my LCD is brockena and some symbols looks not good, I think to exchange it with LED dysplays. Get the dysplays but no time for that. But I remember that the schematic is very interesting for symbol generator for LCD.

[MegaVolt]

The symbols on the LCD is generated from decoder and ROM. I don't remember now , but if I find some time in next days will check the schematic. Maybe you can to find the error on the decoder for this symbol. Just that is in my memories. Because my LCD is brockena and some symbols looks not good, I think to exchange it with LED dysplays. Get the dysplays but no time for that. But I remember that the schematic is very interesting for symbol generator for LCD.

From what I see in the diagram from version "B", the ROM in front of the screen is simply transcoding. It works only towards the side of the screen and has no feedbacks. Those. error in something else.

I have an exchange problem between A2 and A16

[MegaVolt]

I found a problem IC ) This is UART 6402 on the boards A16 and A14.
The complexity was that the chips worked and transmitted data. But not all bits. Part of the bit`s lost somewhere inside the chip. We send 5 accept 1 ))
I managed to find new at $ 0.25 per piece )

Now I see a power error. Further is easier ))

I can tell a little about the exchange check cycle between A16 and A2.

1. A16 sends 0x05 with some period until A2 respond.
2. A2 replies 0x15

I will pay attention to what these two numbers coincide with the fact that they transmit these boards if the switches select testing mode.

Then goes an active exchange. See images.

[Dr. Frank]

Hello,

I've never seen a 5440 with an LCD, so I assumed it was always a VFD.
Are both displays LCDs?
Is this a late modification by FLUKE?
What's the vintage / datecode?
Does anybody have schematics for this change?

How does the front panel look like, as the green filter foil will be changed to something else?

Frank

[MegaVolt]

I've never seen a 5440 with an LCD, so I assumed it was always a VFD.
Are both displays LCDs?
Is this a late modification by FLUKE?
What's the vintage / datecode?

Yes, it has two LCD displays.  This is the very first 5440 with the letter "A".  Based on the date code on the IC, it was produced in the year 83.  I have inserted a video of the same device from velik_kazakov.
https://youtu.be/yJfPx0z0a78

Does anybody have schematics for this change?

The service manual is sold at this address.  http://artekmanuals.com/manuals/other-manuals/
 I am using instructions from 5442A / 5440B and there are differences only on the A2 board.  The rest of the scheme is completely identical.

I can take any photos you are interested in.

[Dr. Frank]

Thank you very much, that's enough of information.
So it's the other way round, that they changed to VFD later.
Frank

[MegaVolt]

Data file with protocol between A16 and A2.

[MegaVolt]

The two Vishay resistors on the A10 board have changed the resistance a lot.  One for 10% and the second for 40%.  As a result, the + 17V power supply was about + 21V.  Replaced with new ones the error has disappeared.  Now the next error )))

I also found that the A9 board has a date of 88.  It looks like it was replaced later.

[MegaVolt]

I just noticed that the error remained the same.  But the LED indicating the error went out.  I don't seem to notice something.

[MegaVolt]

The LCD panel seems to be dead . It's very sad. I don't know how to replace it

[Kleinstein]

A point where those LCDs may fail is with the contacts from the PCB to the glass (zebra strips or gules contacts). There is also a chance a driver chip lew and this may over a long time damage the LCD (e.g. with DC to the display).  Is this actually an LCD or maybe LEDs ?.

[MegaVolt]

There is also a chance a driver chip lew and this may over a long time damage the LCD (e.g. with DC to the display).

The display is almost black and this indicates that the screen itself is damaged.  The electronics are most likely damaged as well.  But it doesn't matter anymore.

Is this actually an LCD or maybe LEDs ?.

No doubt this is an LCD screen.  I specifically shot so that the characteristic tracks to the segments were visible.  Also in the video above you can see the same screen in operation.  There he is also in poor condition, but still shows a couple of digits.

[MegaVolt]

I was able to start the device without errors by pressing the reset key on the front panel.  It looks like there are some problems with the initial launch.  I'll deal with this later.

 The digital test is successful. 

The analog test stops with an error. 

The high voltage test causes a sound of electrical breakdown and the device freezes (  I have not yet found a place with traces of discharges ...

To be continued

[picburner]

According to the manual, this is the area where to look for the fault:

[MegaVolt]

According to the manual, this is the area where to look for the fault:

Thank you )

I turned on the output and even with these errors I see voltages from 20V and below )))) If you select a voltage higher, a guarded power error is triggered.  It looks like these are capacitors.

[picburner]

If the voltages greater than 20V do not work I would check the components highlighted in section A13.

[MegaVolt]

If the voltages greater than 20V do not work I would check the components highlighted in section A13.

Yes. High voltage has problems. I heard breakdown sounds during high voltage self-test.

[MegaVolt]

DAC DIGITAL FAULT
SECOND SWITCH

This error has been fixed. Replacing the optocoupler U18 (HCPL2601) on the A8 board.

The following error may be the reason for running the tests on a cold device )

[MegaVolt]

Warmed up the device. Started the calibration. On high voltage gain calibration, the unit reset and gave an error.

I understand the issue may be that the resistors went a little more than necessary?

[Badwolf]

I also recently repaired a 5440. The diagnostic mode with output on RS232 provides a lot of information and allows you to find your way on the diagram to identify problems. In my case, most of the errors were due to the relay. I didn't replace them ($ 100 each), I just used Dexoit + isopropyl alcohol to remove residue and prevent leakage.

[MegaVolt]

I just used Dexoit + isopropyl alcohol to remove residue and prevent leakage.

Looks like my repair is going to be a little more complicated

I also found that the A9 board has a date of 88.  It looks like it was replaced later.

This change was not an accident. I looked at the reference voltage and was very upset. It looks like the board was already in the hands of a technician and one of the SZA263 is marked with a black marker. This board was put as a known bad one

I also observe oven oscillations that never end

I also checked the output voltages when they were stable. The ratios between 10V and 1000V are very good. Better than I can accurately measure. So there is nothing wrong with the divider resistors.

[Kleinstein]

The oven oscillations are unusual. This is normally a question on how good the initial design is not so much about failing part. There may be a electrolytic cap used in the regulator compensation that may have failed. The other point is too much delay from the heat to the sensor, e.g. from thermal past missing or loose screws.  With a schematics available this should normally be fixable.

For the black dot, this may be from inital selection of the parts. One finds dot's on slected chips quite a lot.

[MegaVolt]

Here are pictures of the inside of the oven.

[MegaVolt]

continue

[MegaVolt]

With a schematics available this should normally be fixable.

What should I change to remove the oscillation?

For the black dot, this may be from inital selection of the parts. One finds dot's on slected chips quite a lot.

It's not like the usual dots. It looks more like it was painted over.

What else could explain this behavior of Vref?

[Dr. Frank]

I also have a (newer) 5442A and investigated on the interesting stacked 13V reference.

This stacking circuit is partly on the small reference board with both SZA263, and partly outside the oven assembly, if I remember correctly.
Maybe you print the different parts of the schematics to understand how this circuit works.

I don't know, where exactly you probe these 13V. W/o extender card it's also not that easy.

I suggest that you connect two cables directly on the reference board choosing ground and  a connection directly at the upper SZA263 output, and then analyze the signal in situ. Pay attention not to create any shorts, especially by proper selection of isolated cables!

I doubt that the SZA263 itself is damaged. Maybe one of the LM308 is breaking down thermally, i.e. one of its input transistors, as the whole assembly is at about 55°C permanently.

Maybe you might also dis - connect the reference board and rebuild the stacking circuit on a test board at room temperature, so you can decide where the failing OpAmp, or other component is sitting. 

Another idea: As the oven might also have problems, check the stability of the supply voltages.

Frank

[MegaVolt]

I also have a (newer) 5442A and investigated on the interesting stacked 13V reference.

They are identical in my opinion.

I don't know, where exactly you probe these 13V. W/o extender card it's also not that easy.

I suggest that you connect two cables directly on the reference board choosing ground and  a connection directly at the upper SZA263 output, and then analyze the signal in situ. Pay attention not to create any shorts, especially by proper selecting of isolated cables!

Here are the connection points.  The only extra element is the relay. Otherwise I have a direct connection to the zener.

I doubt that the SZA263 itself is damaged. Maybe one of the LM308 is breaking down thermally, i.e. one of its input transistors, as the whole assembly is at about 55°C permanently.

Maybe you might also dis - connect the reference board and rebuild the stacking circuit on a test board at room temperature, so you can decide where the failing OpAmp, or other component is sitting.

Thank you for your words. They are encouraging. An op amp is no big deal I'll keep looking

[Kleinstein]

The oven part looks a little odd. It looks like just a simple proportional regulator. As shown it could be relatively sensitive to ripply and noise coming in and not very stable.  As the resistive heater has a square law the loop gain thus goes up with higher heater power. It also looks like the transistor gain would have an effect.

I had expected more like an PI regulator. The high values for R115 / R116 look odd and may be a left over from an original plan to have a capacitor in series to R116. 
My suggestion to fix / improvementthe regulator would be to reduce the gain at higher current. A possible way would be to replace R114 with something like 2x 10 K in series and than something like 3 K and a LED in series to ground from the center. So at the higher end the gain would be reduces about 3 times. This would still be only a small step not a really good solution. A better way would be more like changing to a PI regulator - though tricky with a electrolytic cap (likely need something like 100 µF) at the warm temperature.

[chuckb]

I noticed that the heater is made up of 8 Carbon Comp Resistors.
If their total value has drifted significantly then the heater gain would also change. A lower total resistance would have a higher "voltage to watts" gain.

Is the thermal oscillation present with all the normal insulation and installation in place?
If the heater block is being testing on a cool bench (or even with covers off) it will need a higher voltage to reach temperature and it will have a higher gain from the square law issue.
If it was installed in a warm calibrator the heater will have a lower voltage and less gain from V^2/R.

Good Luck!

[Kleinstein]

The jumpy reference voltage could be from a cold soder joint, failing bond wire or maybe a bad relay contact.

For the heater part the transistor to control the heater is itself a powerful heater.

[MegaVolt]

To get a better understanding I have redrawn the schematics of the Fluke 5440 voltage reference.

[MegaVolt]

Today is a strange day. I found a problematic part. And I should be happy... But it's a R18 fluke 1.68 kOhm unobtanium resistor and I don't know where to get a replacement (((

When you heat it up, it increases many times. I have seen a figure of 27 kOhm. And it takes a very long time to get back to the initial value. The hysteresis in the picture is 0.4 ohms which is 300ppm. Maybe it's a bad contact inside. Does it make sense to fix it?

Maybe someone has a spare pair of 5.18kOhm and 1.68kOhm resistors? Or should I look for all 4 resistors: R18, R22, R19, R21?

[Kleinstein]

The resistors are not that special - mainly trimmed relatively stable resistors. The 5 K part is even not that kritical. The point may be that the resistors can be trimmed / selcted to match the reference chip they are used with. With this resistors one can trim the TC of the reference to a reasonable low value (e.g. < 5 /K). The final precision than comes from a stable temperature.  So one could still search for a suitable value in the 1.4 to 2 K range and than get a relatively good resistor to replace it. I don't know how critical the resistor is exactly, but expect a attenuation similalar to the LTZ1000, so something like an drft attenuation by a factor like 100 to 500. So 100 ppm drift of the resistor would translate to 0.2 to 1 ppm change in ref. voltage.

At least for the start a relatively normal resistor can do.

[MegaVolt]

While I'm looking for a replacement resistor I tested the rest.

Some show stable hysteresis to one side. For example, the resistor in the picture adds 5ppm after each heating.

As a result after 20 turns on of the device we will have 100 ppm. I think this is a lot.

Is it worth to change such resistors?

[MegaVolt]

I returned

1. Corrected the scheme. C5 fixed to C16.
2. I drew a board with tracks. (this file is for Photoshop layered. Let me know if you need it >50MB)

[leighcorrigall]

...

For the black dot, this may be from inital selection of the parts. One finds dot's on slected chips quite a lot.

It's not like the usual dots. It looks more like it was painted over.

...

The black dot does appear on another reference board that I have. It may help distinguish one SZA263 from the other when selected resistors are being installed.