[volt-nuts] Fluke 5200A repair

Gerd admin at controlelectronics.com.au
Thu Jul 10 04:25:32 EDT 2014


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 at controlelectronics.com.au>
> To: Discussion of precise voltage measurement <volt-nuts at febo.com>
> Subject: Re: [volt-nuts] Fluke 5200A repair.
> Message-ID: <53BD3362.5030802 at 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 at controlelectronics.com.au>
>> To: volt-nuts at febo.com
>> Subject: Re: [volt-nuts] Fluke 5200a
>> Message-ID: <53BB3BA7.2070102 at 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
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<http://www.controlelectronics.com.au/>*
Email*: admin at controlelectronics.com.au 
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