Fluke 5200A repair
Hi Gerd,
R6 slider to U1 varies from +15v to -15v but the output of U1 only
varies by mv's, I put this down to the loading of R9 to earth on the input
to pin3 of U1 (221 ohm),only allowing a small variation to the input on pin
3 of U1, maybe this needs further investigation!
I initially suspected U1 but when you look up the markings on the IC on the
internet nothing can be found for it as it was specific to Fluke and is no
longer available.
I did substitute an OP7 IC but it did not make any difference. Just today I
got an email from Fluke telling me that part is no longer available, but
they kindly sent me the full specs for it as I requested and it turns out to
be an OP77 according to their sheet, so if the OP77 was faulty the OP7
should have at least given me some improvement which it did not.
This afternoon I tried the shotgun approach and changed all the diodes
(zener's included) except for the 130v zener as I did not have one. It made
no difference.
I think I have tested all the transistors in those stages and I did find two
of them u/s as stated earlier, but maybe I missed one.
I have measured all the resistors around there to and replaced any that were
too far out.
Checked all the caps to make sure none of them were shorted and the few
electros for ESR and capacitance, all appear to be ok.
What do you think of the voltage variation out of U1, should it be more? I
would have thought so but maybe I am wrong.
Thanks again for your input.
Ken.
Message: 6
Date: Wed, 09 Jul 2014 22:19:46 +1000
From: Gerd admin@controlelectronics.com.au
To: Discussion of precise voltage measurement volt-nuts@febo.com
Subject: Re: [volt-nuts] Fluke 5200A repair.
Message-ID: 53BD3362.5030802@controlelectronics.com.au
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Hello Ken,
Glad to hear the SpecAn is still going well.
I know working on these machines without extender boards is a pain. I
assume U1 output is moving as you adjust R6. U1 feeds a differential
cascode circuit consisting of Q3,4,5,and 6. these would have been
matched originally for minimum offset. It could be they are no longer
matched close enough for the offset adjustment to compensate. It could
be U1 also.
If CR3 anode is -31.8V that means Q9 must be cutoff. Probably the
quickest is to check every transistor in the input and mid stage
amplifiers. Also check every carbon resistor, at this age they will all
be out of tolerance, sometimes quite a bit.
Regards
On 09/07/14 09:10, Kgoodhew wrote:
Hi Gerd,
Thanks for the reply.
My mistake I should have said r6 and not r26 as I typed it from memory.
The voltages that are high are :-
Q2 collector 7.35v
Q3-Q4 emitters 2.0v-3.2v should be nearly equal and about 0.7 to 1.8v
Q5 Q7 collectors -38.0v should be +28.4v
CR3 anode -31.8v should be -20 to -22v
Originally found Q36 and Q37 faulty apparently caused by intermittent bad
contacts on the plug in base on Q15 as I could hear arcing from here
after
powering up the unit and found the plastic plug in base melted, the
transistor tested ok so I just removed the base and soldered it into the
pcb.
During my investigations I found and relaced several out of tolerance
resistors as well as CR19 -CR20 zener's one of which was breaking down
well
below it's 20v rating. Also found Q33 faulty.
Originally I had to replace a number of components in the power supply
regulator board including caps and the U2 regulator for the +19v and +5v
supplies as well as a few tracks that had been damaged by someone's
earlier
repair attempts, to get the unit to operate at all.
The unit output is pretty close according to my HP3478A, it is just that I
have this 1mv offset on the output that I cannot adjust out using R6.
As I do not have an extender board to do testing with the board out of the
chassis it has been a long and painful process to remove the board and
solder wires on to each point to make measurements that I need each time.
I even tried to get the sockets to make an extender board but it appears
the
43/86 pin sockets at the required pin spacing are no longer available.
BTW the HP8569B you repaired for me some time ago is still going strong.
Today's Topics:
1. Re: Fluke 5200a (Gerd)
2. Re: Buying HP-3458A (Todd Micallef)
3. Re: Fluke 5200a (John Phillips)
Message: 1
Date: Tue, 08 Jul 2014 10:30:31 +1000
From: Gerd admin@controlelectronics.com.au
To: volt-nuts@febo.com
Subject: Re: [volt-nuts] Fluke 5200a
Message-ID: 53BB3BA7.2070102@controlelectronics.com.au
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Hello Ken,
From what I remember of this circuit, R26 is for output stage bias. R6
is
for adjusting offset. By the way, which voltages are high and how much?
The 5200 is an old beast, expect a lot of marginal electrolytics, carbon
resistors that have drifted well out of tolerance and even transistors
that
no longer perform any where near what they originally did.
Regards
On 07/07/14 14:56, Ken Goodhew1 wrote:
Hi all,
I am currently repairing a Fluke 5200a ac voltage
calibrator.
After pulling cards in and out and soldering multiple wires on to test
I now have the unit working about 98%.
Anybody might have or know of where I might be able to obtain an
extender card for this unit as it would make it a lot easier to fix
the last remaining problem that I have, ie:- I have a dc offset
voltage on the output of about 1mv when it should be +/- 100 microvolts.
I am unable to adjust this with r26 adjustment on the power amplifier
board as described in the manual. I have followed the troubleshooting
guides as per the manual, as well as testing just about all the
components around that particular part of the circuit.
The problem appears to be that the input stage is not being turned on
hard enough as all the suggested voltages for the input stage
(Q1-2-3-4-5-9) are all too high. The supply voltages are all within spec.
Anybody can offer suggestions?
Sorry to put this out there in this group but I cannot find an online
group related to fluke test equipment to ask.
Ken Goodhew.
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Quality used test equipment
Phone: 02 9456 0736
Website: www.controlelectronics.com.au
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Ken wrote:
R6 slider to U1 varies from +15v to -15v but the output of U1 only
varies by mv's, I put this down to the loading of R9 to earth on the input
to pin3 of U1 (221 ohm),only allowing a small variation to the input on pin
3 of U1, maybe this needs further investigation!
Look at the circuit. The 100k potentiometer (R6) feeds a voltage
divider composed of R8 and R9 (464k and 221 ohms, respectively). The
tap of this divider feeds the reference input of U1. R8 and R9
attenuate the +/- 15v range of R6 by a factor of 210, so the divider
tap voltage (i.e., the reference voltage for U1) only varies +/- 7.14
mV from ground for the full range of R6.
U1 is an integrator, so it has lots of gain at DC (Q38 switches the
integrating capacitor to give two time constants). If one of these
capacitors is leaky or shorted (or there is another leakage path from
Pin 6 to Pin 2 of U1), it would reduce the gain of the integrator and
could produce the symptom you are having.
Best regards,
Charles
Hello Ken,
The offset adjustment is about +-7mV to the input of U1. The amplifier
has a gain of 3 or 30 so adjustment is small. Is the problem the same on
both the 10V and 100V ranges? Is the amplifier producing the full output
voltage? Is it distortion free?
Are both the 190V regulators working correctly?
Regards
On 09/07/14 23:19, Kgoodhew wrote:
Hi Gerd,
R6 slider to U1 varies from +15v to -15v but the output of U1 only
varies by mv's, I put this down to the loading of R9 to earth on the input
to pin3 of U1 (221 ohm),only allowing a small variation to the input on pin
3 of U1, maybe this needs further investigation!
I initially suspected U1 but when you look up the markings on the IC on the
internet nothing can be found for it as it was specific to Fluke and is no
longer available.
I did substitute an OP7 IC but it did not make any difference. Just today I
got an email from Fluke telling me that part is no longer available, but
they kindly sent me the full specs for it as I requested and it turns out to
be an OP77 according to their sheet, so if the OP77 was faulty the OP7
should have at least given me some improvement which it did not.
This afternoon I tried the shotgun approach and changed all the diodes
(zener's included) except for the 130v zener as I did not have one. It made
no difference.
I think I have tested all the transistors in those stages and I did find two
of them u/s as stated earlier, but maybe I missed one.
I have measured all the resistors around there to and replaced any that were
too far out.
Checked all the caps to make sure none of them were shorted and the few
electros for ESR and capacitance, all appear to be ok.
What do you think of the voltage variation out of U1, should it be more? I
would have thought so but maybe I am wrong.
Thanks again for your input.
Ken.
Message: 6
Date: Wed, 09 Jul 2014 22:19:46 +1000
From: Gerd admin@controlelectronics.com.au
To: Discussion of precise voltage measurement volt-nuts@febo.com
Subject: Re: [volt-nuts] Fluke 5200A repair.
Message-ID: 53BD3362.5030802@controlelectronics.com.au
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Hello Ken,
Glad to hear the SpecAn is still going well.
I know working on these machines without extender boards is a pain. I
assume U1 output is moving as you adjust R6. U1 feeds a differential
cascode circuit consisting of Q3,4,5,and 6. these would have been
matched originally for minimum offset. It could be they are no longer
matched close enough for the offset adjustment to compensate. It could
be U1 also.
If CR3 anode is -31.8V that means Q9 must be cutoff. Probably the
quickest is to check every transistor in the input and mid stage
amplifiers. Also check every carbon resistor, at this age they will all
be out of tolerance, sometimes quite a bit.
Regards
On 09/07/14 09:10, Kgoodhew wrote:
Hi Gerd,
Thanks for the reply.
My mistake I should have said r6 and not r26 as I typed it from memory.
The voltages that are high are :-
Q2 collector 7.35v
Q3-Q4 emitters 2.0v-3.2v should be nearly equal and about 0.7 to 1.8v
Q5 Q7 collectors -38.0v should be +28.4v
CR3 anode -31.8v should be -20 to -22v
Originally found Q36 and Q37 faulty apparently caused by intermittent bad
contacts on the plug in base on Q15 as I could hear arcing from here
after
powering up the unit and found the plastic plug in base melted, the
transistor tested ok so I just removed the base and soldered it into the
pcb.
During my investigations I found and relaced several out of tolerance
resistors as well as CR19 -CR20 zener's one of which was breaking down
well
below it's 20v rating. Also found Q33 faulty.
Originally I had to replace a number of components in the power supply
regulator board including caps and the U2 regulator for the +19v and +5v
supplies as well as a few tracks that had been damaged by someone's
earlier
repair attempts, to get the unit to operate at all.
The unit output is pretty close according to my HP3478A, it is just that I
have this 1mv offset on the output that I cannot adjust out using R6.
As I do not have an extender board to do testing with the board out of the
chassis it has been a long and painful process to remove the board and
solder wires on to each point to make measurements that I need each time.
I even tried to get the sockets to make an extender board but it appears
the
43/86 pin sockets at the required pin spacing are no longer available.
BTW the HP8569B you repaired for me some time ago is still going strong.
Today's Topics:
1. Re: Fluke 5200a (Gerd)
2. Re: Buying HP-3458A (Todd Micallef)
3. Re: Fluke 5200a (John Phillips)
Message: 1
Date: Tue, 08 Jul 2014 10:30:31 +1000
From: Gerd admin@controlelectronics.com.au
To: volt-nuts@febo.com
Subject: Re: [volt-nuts] Fluke 5200a
Message-ID: 53BB3BA7.2070102@controlelectronics.com.au
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Hello Ken,
From what I remember of this circuit, R26 is for output stage bias. R6
is
for adjusting offset. By the way, which voltages are high and how much?
The 5200 is an old beast, expect a lot of marginal electrolytics, carbon
resistors that have drifted well out of tolerance and even transistors
that
no longer perform any where near what they originally did.
Regards
On 07/07/14 14:56, Ken Goodhew1 wrote:
Hi all,
I am currently repairing a Fluke 5200a ac voltage
calibrator.
After pulling cards in and out and soldering multiple wires on to test
I now have the unit working about 98%.
Anybody might have or know of where I might be able to obtain an
extender card for this unit as it would make it a lot easier to fix
the last remaining problem that I have, ie:- I have a dc offset
voltage on the output of about 1mv when it should be +/- 100 microvolts.
I am unable to adjust this with r26 adjustment on the power amplifier
board as described in the manual. I have followed the troubleshooting
guides as per the manual, as well as testing just about all the
components around that particular part of the circuit.
The problem appears to be that the input stage is not being turned on
hard enough as all the suggested voltages for the input stage
(Q1-2-3-4-5-9) are all too high. The supply voltages are all within spec.
Anybody can offer suggestions?
Sorry to put this out there in this group but I cannot find an online
group related to fluke test equipment to ask.
Ken Goodhew.
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sig.html Control Electronics Pty Ltd
The home of Shiftmaster
Quality used test equipment
Phone: 02 9456 0736
Website: www.controlelectronics.com.au
http://www.controlelectronics.com.au/*
Email*: admin@controlelectronics.com.au
mailto:admin@controlelectronics.com.au
ABN 86 109 858 022
The email addresses in this message are not to be added to any database,
list, or mailing list without my prior explicit written permission. This
email and any files transmitted with it are confidential and intended
solely
for the use of the individual or entity to whom they are addressed. If you
have received this email in error please notify the system manager. Please
note that any views or opinions presented in this email are solely those
of
the author and do not necessarily represent those of the company. Finally,
the recipient should check this email and any attachments for the presence
of viruses. The company accepts no liability for any damage caused by any
virus transmitted by this email.
This email is free from viruses and malware because avast! Antivirus
protection is active.
and follow the instructions there.
--
sig.html Control Electronics Pty Ltd
The home of Shiftmaster
Quality used test equipment
Phone: 02 9456 0736
Website: www.controlelectronics.com.au
http://www.controlelectronics.com.au/*
Email*: admin@controlelectronics.com.au
mailto:admin@controlelectronics.com.au
ABN 86 109 858 022
The email addresses in this message are not to be added to any database,
list, or mailing list without my prior explicit written permission. This
email and any files transmitted with it are confidential and intended
solely for the use of the individual or entity to whom they are
addressed. If you have received this email in error please notify the
system manager. Please note that any views or opinions presented in this
email are solely those of the author and do not necessarily represent
those of the company. Finally, the recipient should check this email and
any attachments for the presence of viruses. The company accepts no
liability for any damage caused by any virus transmitted by this email.