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Fixed My DRO! whoo hooo!

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  • #16
    You probably had a cold solder joint on the resistor, so it was "making and breaking" at random intervals. The heat caused the part to expand enough into the solder to make a better connection.

    I doubt that the resistor is bad, or even damaged - those things are near bullet proof. I mess with SMT components like that all the time and I can't remember a time where I found a SMT resistor bad, except from over powering them and this guy is just in the signal path.

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    • #17
      SLK --- After testing I then hit that 161 from both sides with my iron before removing it - just a blip and seeing the reformation of solder to make sure it was grounded good, and it did look soldered very well even before that, there was no change in my test readings...

      I did the same thing with testing the Y's 161 and totally different readings, not heating it - just measuring it --- and even after removal of the 161 on the X it read the same as when it was on board --- it was only 12.something where as the Y's was 180. something --- the X was 12. something both on and off the board (11.38 off and after cooling and in maybe little different room temp) so there's nothing upstream or downstream that was effecting things (both X and Y leads disconnected from the display unit when testing this)

      there was stark contrast between this resistor and the one on the Y board in the same location,,, not only that --- after repairing and replacing the resistor the leads from the end where it plugged into the display started looking similar to each other - the yellow and black almost matched the resistance reading... then I fired things up and sure nuff everything worked right off the bat and has not even glitched once... that has never happened in about two years with all the paces i put things through I would have had a glitch by now....

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      • #18
        Originally posted by mickeyf View Post
        Congratulations!
        And, you have beaten half-nuts Mattthemuppet for finally solving the painfully frustrating long-running puzzler of the month!
        and that reminds me of another song fragment "Adolf Hitler only had one ball, the other was stored in the Albert Hall"

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        • #19
          Good fix. And that always leads to a real feel good feeling. Believe me, I know.

          On that auto-ranging meter, there should be a decimal point in the display that tells you the actual value. Play with it and some known value resistors and you will get the hang of it.
          Paul A.
          SE Texas

          And if you look REAL close at an analog signal,
          You will find that it has discrete steps.

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          • #20
            Hot air soldering irons are the bomb for surface mount stuff, if you have one.

            -D
            DZER

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            • #21
              I checked it last night after everything got acclimated to the cooler temps in the basement - it was solid not even a .001" glitch after going full blown spastic with the handles,


              same thing with this morning --- what puzzles me is that the Y is involved too and totally glitch free - is there a common relationship between both scales that could have been effected with what I did?


              I think im getting another steak today for a celebration repeat as this has been one long haul and I think I just saved allot of money....

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              • #22
                I think you are just like your pit bull dogs! You get a hold of something and won't let go. To say I am impressed that you stuck to it and actually fixed the DRO would be a big understatement!
                Location: The Black Forest in Germany

                How to become a millionaire: Start out with 10 million and take up machining as a hobby!

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                • #23
                  Thanks BF, had not much to do with skill - and everything to do with persistence and determination and also getting lucky,

                  and now for the confession that will most likely make the electronic guys cringe,,, remember the "crystal" that I was fixated on because i could not get a reading off of it?

                  well i removed it and put one in from another board just to see what would happen - I thought if it was just a frequency setter of sorts then who knows things would just compute slower or faster but maybe stable if the original was bad,,,,,,,,, well the whole thing went wonky --- no scales picking up anything and the digital readout was not even numbers just here and there jumbles of light... I thought I f'ed it up right then and there but when i put the original crystal back everything went back to normal (including the glitch)

                  I do not see any blistering on the old 161 SMT so don't know why it shot craps,,,

                  but over the years I have found about 5 SMT's that were bad in two separate incidences --- it was not "their fault" although in comparison to some of their ceramic counterparts it does expose a weakness, all were in tape deck/CD players and after finding paths that were totally "open" that also led to corrosive looking goo and in one case even that green fungus that you see on positive side battery terminals I then replaced however many it took from other cannibalized decks and got things up and running again, talked to the customers when they picked up their cars and in one case even got a giggle from a customer about his wife who had a major"pepsi" spill the previous year in her cup holder that was positioned directly above the kenwood CD player...
                  That unit had a special adapter that went to some kinda "sirus"? pick up unit with special harnessing and in fact I checked around and all the stereo guys stated I just needed to replace the entire mess and rewire to boot, it would have been over a grand to do and I think they got by with 120 dollar bill...

                  I have been doing hillbilly electronics repair for decades --- big emphasis on the hillbilly part lol and also --- I don't always win...

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                  • #24
                    Originally posted by A.K. Boomer View Post
                    nd now for the confession that will most likely make the electronic guys cringe,,, remember the "crystal" that I was fixated on because i could not get a reading off of it?

                    well i removed it and put one in from another board just to see what would happen - I thought if it was just a frequency setter of sorts then who knows things would just compute slower or faster but maybe stable if the original was bad,,,,,,,,, well the whole thing went wonky...
                    The crystals perform a delicate choreographed dance to enable your DRO to work. They set the rates at which data is bantered around the board. It sets the time that data will arrive somewhere needed. If you speed things up, or slow things down, the data hand-off doesn't occur at the correct time and the data is lost (gets wonky). That's how we knew that the crystals weren't the problem - if they were not working, your entire DRO wouldn't work.

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                    • #25
                      SLK so would it be fair to say they are the "starting point" and all other components that are susceptible to this frequency have to be built around them, anotherwords you don't build an entire board with a multitude of different components and then pick out a crystal --- you pick out the crystal and then match all other critical components to it ----?

                      im thinking I missed a step --- you start with the main processor or component it takes to make the board do all the things it needs to do in the first place then match the crystal and then all the other components and secondary processors to it???
                      Last edited by A.K. Boomer; 03-09-2021, 12:50 PM.

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                      • #26
                        The crystal frequency is generally not critical, although serial communications need a specific clock rate. Most processors specify a range of clock frequencies and may even work on DC (toggling the clock manually). If the interface to the peripherals like the display uses RS-232 serial comms, a clock frequency more than 5-10% off will cause "framing errors" and will be evidenced by erratic operation as you have seen. The processors have internal settings that can be changed to work with various crystal frequencies, and they also often have internal oscillators so an external crystal may not be needed.

                        The design process involves many choices, but the clock frequency and crystal selection come very early. Usually you want to use the highest rated frequency so that processing can proceed quickly, but you also need to consider such things as the desired baud rate, which should be among a limited set of choices. I often use 14.7456 MHz, which can be divided by integers to obtain common values like 2400, 4800, 9600, 19200, and 38400, and 57600. Corresponding divisors are 6144, 3072, 1536, 768, 384, and 256.
                        http://pauleschoen.com/pix/PM08_P76_P54.png
                        Paul , P S Technology, Inc. and MrTibbs
                        USA Maryland 21030

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                        • #27
                          You catz are amazing - the more I scratch the surface the more I want to just pop the hood on an engine lol

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                          • #28
                            Can you say, "Modem Baud Rates"?



                            Originally posted by PStechPaul View Post
                            The crystal frequency is generally not critical, although serial communications need a specific clock rate. Most processors specify a range of clock frequencies and may even work on DC (toggling the clock manually). If the interface to the peripherals like the display uses RS-232 serial comms, a clock frequency more than 5-10% off will cause "framing errors" and will be evidenced by erratic operation as you have seen. The processors have internal settings that can be changed to work with various crystal frequencies, and they also often have internal oscillators so an external crystal may not be needed.

                            The design process involves many choices, but the clock frequency and crystal selection come very early. Usually you want to use the highest rated frequency so that processing can proceed quickly, but you also need to consider such things as the desired baud rate, which should be among a limited set of choices. I often use 14.7456 MHz, which can be divided by integers to obtain common values like 2400, 4800, 9600, 19200, and 38400, and 57600. Corresponding divisors are 6144, 3072, 1536, 768, 384, and 256.
                            Paul A.
                            SE Texas

                            And if you look REAL close at an analog signal,
                            You will find that it has discrete steps.

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                            • #29
                              As far as the crystal frequency is concerned, it can be both ways. Many, well designed digital circuits will continue to operate with a range of frequencies from literally single stepping them (one clock pulse at a time, manually controlled) up to two or more times the design frequency. Many computers have had the clock frequency increased by changing the crystal. No guarantee from the OEM, but it was done with varying degrees of success.

                              On the other hand, I have seen digital devices where the designers were pushing the envelope right from scratch and things went bad just from the ageing of the ICs and other components in them. When asked for advise, those design engineers replied to try changing some of the more critical ICs for the corresponding one of a different logic series. Faster or slower chips that did the same thing were used to "tune" the circuit to work. Not a good design, but it does happen. Changing the clock frequency can have much the same effect. But, at best, it's a crap shoot.
                              Paul A.
                              SE Texas

                              And if you look REAL close at an analog signal,
                              You will find that it has discrete steps.

                              Comment


                              • #30
                                A lot depends on what the "other" crystal's frequency was. And if there are any more.

                                If there is ONE crystal in the entire device, then it is a lot less fussy (often) than if there are two. Two must be coordinated. Especially if one affects communication that the other must receive.

                                One, may co-ordinate everything to itself. But a different frequency may simply not work, or it may be everywhere all over, which it sounds like yours was, possibly because it was not stable, or it asked for things the hardware could not do. (or there may actually be two of them, and now your second one was way out of synch)
                                CNC machines only go through the motions.

                                Ideas expressed may be mine, or from anyone else in the universe.
                                Not responsible for clerical errors. Or those made by lay people either.
                                Number formats and units may be chosen at random depending on what day it is.
                                I reserve the right to use a number system with any integer base without prior notice.
                                Generalizations are understood to be "often" true, but not true in every case.

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