FLUKE 5500A REPAIR  - Page 1
Forum section: electronics / repair

author: HUGOMAN
author_rank: Regular Contributor
timestamp: January 10, 2022, 10:47:46 pm
content: Hi to everyoneThis calibrator gives error 1503 when i generate 1V or 10 ohm then it gives a second message 399 who is A/D COMM is the issue.welcome to your ideas and experiences big thanks to youRegards

author: Kim Christensen
author_rank: Super Contributor
timestamp: January 10, 2022, 10:53:13 pm
content: It may not even be a resistor network...If you post the make and model number of the unit that this PCB is from, it may get you better responses.

author: abdulbadii
author_rank: Frequent Contributor
timestamp: January 10, 2022, 11:04:59 pm
content: you, I, we read it Zzener diodes net beside jack/jumper (JK)?

author: HUGOMAN
author_rank: Regular Contributor
timestamp: January 10, 2022, 11:28:24 pm
content: This one is in the board A6 of FLUKE 5500A, it is ceramic package and the reference printed there is 946087.Thanks

author: Kim Christensen
author_rank: Super Contributor
timestamp: January 11, 2022, 12:07:12 am
content: I found a schematic.Looks like it is a custom resistor network for Fluke.

author: coromonadalix
author_rank: Super Contributor
timestamp: January 11, 2022, 12:20:21 am
content: The obvious source would be Fluke send them an email, its a custom madeYou wont get it, unless you buy an a6 board for parts and this network resistor is good,seems to have been tampered, huge solder amount on the pins

author: HUGOMAN
author_rank: Regular Contributor
timestamp: January 11, 2022, 09:10:39 am
content: Sure they can sell me the A6 board ? do you have an idea about price ? awsome

author: max-bit
author_rank: Frequent Contributor
timestamp: January 11, 2022, 11:11:10 am
content: The module is made to order - read unless you buy, for example, on ebay (used - functional) otherwise rather impossible to get

author: coromonadalix
author_rank: Super Contributor
timestamp: January 11, 2022, 03:34:24 pm
content: Or try to carefully desolder it, and try to measure all the resistors on the given schematic pinout ?? if one value is busted, maybe try a substitution in paralell

author: HUGOMAN
author_rank: Regular Contributor
timestamp: January 11, 2022, 03:39:16 pm
content: THANK YOU SIRi think the samething but i am still guessing about power of resitor that i will put 1/4 watts for the tol i will put 1%?Do You agreed with this plan?All The Best

author: coromonadalix
author_rank: Super Contributor
timestamp: January 11, 2022, 06:16:12 pm
content: Well to do some test it should do the jobBut for precision wise, it will not do if you intend to do scope calibration after the repairsYou need to know when its possible the resistors caracteristics / precision / tempco tolerance .... to do a correct substitution

author: alm
author_rank: Super Contributor
timestamp: January 11, 2022, 07:28:21 pm
content: I don't know the function of the A6 board, but it may well be that they are using a hybrid for temperature coefficient matching and thermal matching of the different resistors, so their ratios stay context (like in a voltage divider). In that case, trying to supplement the original resistor with a series / parallel resistor (if the original drifted but is stable now) might be best. Otherwise, I expect that a low tempco precision wirewound for Vishay bulk metal foil to be a closer match than a 1% resistor. But of course for an initial test you can use something more basic. It would not surprise me if it fails self calibration / self test with a lower spec resistor.It's a higher spec calibrator, but TiN writes about the Fluke 5700A thatthe resistors on the Ohms board have a temperature coefficient up to 1 ppm/°C. Your 1% resistors might be hundred times worse.

author: HUGOMAN
author_rank: Regular Contributor
timestamp: January 11, 2022, 10:00:11 pm
content: the problem is those kind of components could not be found everywhere, i will tell more details about this calibrator issue, i don't know if i continue here or i make a new post?Thanks

author: alm
author_rank: Super Contributor
timestamp: January 11, 2022, 10:07:25 pm
content: I suggest creating a new post and linking to this thread in the first post. In that post, do an as good possible job of describing the state of the unit, history if known and current symptoms.If you continue with this thread, at least change the title of the first post to something more meaningful like "Fluke 5500A repair"

author: coromonadalix
author_rank: Super Contributor
timestamp: January 12, 2022, 02:02:48 am
content: Instead of strating a new threadSimply change your first thread title ''Re: UNKOWN RESISTOR HELP'' to a FLUKE 5500A repair ?? I dont think the mods would be angry ?

author: CaptDon
author_rank: Super Contributor
timestamp: January 12, 2022, 03:49:41 am
content: It is of course a laser trimmed ceramic resistor network. Done so they could be trimmed to better than 1% tolerance, sometimes to .1% tolerance. Love the Z=Zener network reply, hehehe, not hardly, if it were you would see the bulges and it would be overlaid in the typical green epoxy.

author: HUGOMAN
author_rank: Regular Contributor
timestamp: January 12, 2022, 08:30:39 am
content: YES OK

author: CaptDon
author_rank: Super Contributor
timestamp: January 12, 2022, 02:53:27 pm
content: We often see 'Z' as representing the impedance of a 'network' and somehow these hybrid resistor 'networks' are indicated with a Z. As in Z1, Z2 etc. on the artwork and in the schematic. Many years ago they used to use customized modules with resistors, capacitors, diodes, transistors and even specialized I.C.'s to save space. They were ceramic hybrids often with printed laser trimmed resistors and generally coated with green epoxy and also often a brownish yellow encapsulation. In the television and radio circles they were often called 'Plates'. I have seen schematics marked as "HY' or 'HM' (Hybrid Module) and often seen them called 'I.C.' as in I.C. 10 etc. Among Zenith and many others they would not release any information on what was contained in the 'plate' and when these went bad and were no longer available that was an end-of-life for your device. So reverse engineering them became very common. Case in point, the 'greenie' used in Tektronix TDS420 power supplies. An 'unobtainium' part even since the day those scopes were released. They have been reverse engineered and can be duplicated today. Besides being space saving these little wonders often protected a product from being easily duplicated. Cheers!!

author: HUGOMAN
author_rank: Regular Contributor
timestamp: January 12, 2022, 08:16:11 pm
content: Quote from: HUGOMAN on January 10, 2022, 10:47:46 pm

author: HUGOMAN
author_rank: Regular Contributor
timestamp: January 13, 2022, 08:15:05 am
content: Hi to everyoneThis calibrator gives error 1503 when i generate 1V or 10 ohm then it gives a second message 399 who is A/D COMM is the issue.welcome to your ideas and experiences big thanks to youRegards

author: Kim Christensen
author_rank: Super Contributor
timestamp: January 13, 2022, 07:29:45 pm
content: If I was attempting to fix this, I would determine which resistor(s) in Z8 is open and temporarily bridge an equivalent one across. (Series/parallel/pot combo to get the right value)Then see if the error messages go away. If not, then you have other things to fix as well.

author: HUGOMAN
author_rank: Regular Contributor
timestamp: January 13, 2022, 08:22:42 pm
content: Hi Mr KIM first thanks for your positif messagei am going on and i am sure that i will arrive. i will let you know the final status.1 thingto get your point of view:does the digital curve tester help to find really the defective component or just commercial testers! i mean the manual method remains the best!what do you think ? i ask everyone about this.Best Regards and thanks for this forum's Dave

author: Kim Christensen
author_rank: Super Contributor
timestamp: January 13, 2022, 09:54:46 pm
content: Quote from: HUGOMAN on January 13, 2022, 08:22:42 pmWhich digital curve tester are you using? Model number? Or picture of it.

author: HUGOMAN
author_rank: Regular Contributor
timestamp: January 13, 2022, 09:59:26 pm
content: no not yet i plan to buy it but i dont have it yet. so maybe it helps ?

author: dcmxx
author_rank: Contributor
timestamp: May 17, 2022, 06:14:48 pm
content: Hi. a little bit off topic. but I'm looking for a A9 Main CPU board for a 5500a calibrator. If someone has one to sell i might be interested in purchasing it

author: gwideman
author_rank: Contributor
timestamp: February 16, 2023, 06:01:32 am
content: In case anyone else stumbles in here with a question about Z8 and what it does: Definitely check the schematic in post #4.The relays K6,7,8, select which voltage will be delivered to the VMID output, which ultimately is connected (via backplane board and relay) to the front panel "Normal High" output terminal. Depending on which of K6, K7 and K8 are enabled, VMID either seesa 3.3V-range voltage direct from U42 and R67or a divide-by-10 version of that provided by Z8 pin 1 voltage divider (hence 330mV range)or a divide-by-100 version provided by Z8 pin 5, (hence 33mV range)Nothing very sophisticated here, just plain old resistive dividers with output impedance 50 ohms (and of course sophisticated accuracy, temperature matching etc).But of some note is that since this Z8 resistor network gets directly connected to the output terminal, it's relatively easy to damage it. For example, while setting the calibrator to output say 300mV, an accidental connection to external 5V supply would deliver 0.5W into Z8, which it's probably not designed to handle.