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  • Opamp test circuits

    I'm going to build myself a battery powered pocket tester to take to the shop next time I buy opamps.

    This looks like it might be suitable.
    Attached Files
    Building a better world (one tube amp at a time)

    "I have never had to invoke a formula to fight oscillation in a guitar amp."- Enzo

  • #2
    Interesting, but ... what are they supposed to do?

    What will a good vs. a bad Op Amp show?
    Juan Manuel Fahey

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    • #3
      There are times when I think such a gizmo could be useful for me, like hopefully save me from wasting my time going to the electronics store in town and buying dud opamps and having to go back to the store to buy more opamps (or swap the duds).

      (I just swore and cursed my way through repairing an SVT-CL which had multiple failures including op-amps (for the comparators in the bias sensor circuit) that needed replacement. As I have fixed the amp all nicely now, I'm not in too much of a hurry to build a portable tester, so its relegated to one of those 'maybe' projects)
      Building a better world (one tube amp at a time)

      "I have never had to invoke a formula to fight oscillation in a guitar amp."- Enzo

      Comment


      • #4
        Well, I am still of the opinion that one of the most utterly basic little throw-away practice amps will make a fine one. There is usually one dual op amap inside, which replace with a socket. Then try any one you like in there.
        Education is what you're left with after you have forgotten what you have learned.

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        • #5
          The test circuits shown will still work even if there's a significant DC offset at the output, and this is one of the most common failure modes. Besides other things, they also don't operate the component at the usual +/- 15V.

          I think a tester that would give confidence in the IC being 100% would be quite complex.

          Comment


          • #6
            Maybe I was lucky but I never ever bought a bad Op Amp and would be very surprised that any got through factory QC .

            Not saying that others can't get a bad one, of course.

            I worry that shop testing might not be recognized by shop owners or salesmen, as in: "hey!!!! , I gave you a good one .... you just damaged it with your gizmo !!!!! "
            Juan Manuel Fahey

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            • #7
              Same here - I can't recall ever having a bad one from new. But who knows what happens to the ones that fail quality checks at the factory?

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              • #8
                Originally posted by Mick Bailey View Post
                Same here - I can't recall ever having a bad one from new. But who knows what happens to the ones that fail quality checks at the factory?
                Selling such circuits would destroy factory reputation - I think that they are destroyed at the factory. I also can't recall having a bad opamp from new (and I bought at least a thousand or more). The only chance to buy such opamps is to buy them from suspected guys from ebay, or directly from China. So building such a test jig is a waste of time and money.
                On the other hand, it is very easy (in most cases) to verify that the opamp has failed. Especially in case that Tubeswell had: failed TL074 working as a comparator. You just measure two input voltages and verify whether the output voltage is correct.

                Mark

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                • #9
                  FWIW semiconductors travel all over the World, and are testad at every single "station" , as part of the work performed there (not one by one but following accepted statistical QC).

                  I had read this a couple Months ago when arguing the old "Chinese Bad ... USA good" discussion.
                  In a nutshell: even if a semiconductor is bad and marked "China" .... there's way too many multinational hands involved in its fabrication, the path is mind boggling, and that's an understatement.

                  From HQ W968421 - Country of Origin Marking Requirements for Semiconductor Devices; Multiple Country Disjunctive Marking; 19 U.S.C. 1304; 19 CFR 134.46 - United States International Trade Commision Rulings
                  this is a 2007 explanation by AMD headquarters about some trade problems they had at the time, I bet today it's even more complicated.

                  This is not "something posted on a hobbyist's Forum" but an official answer to "United States International Trade Commision Rulings And Harmonized Tariff Schedule" , a high level US Govt Agency:

                  Cut and paste:
                  RE: Country of Origin Marking Requirements for Semiconductor Devices; Multiple Country Disjunctive Marking; 19 U.S.C. 1304; 19 CFR 134.46
                  AMD is an importer of semiconductor devices. AMD’s semiconductor devices are typically made in China, Korea, Malaysia, and Taiwan from wafers that are diffused in Germany, Singapore, Taiwan and Japan. (obviously tested there)
                  AMD has its semiconductor devices diffused in Germany or Singapore. After these semiconductors are diffused, they are shipped to Malaysia where they are cut. When the cutting of the wafers is completed, the dies can be handled in two distinct processes. In Malaysia, the chip capacitor will be attached, testing will be performed, and the lid will be attached. Then the processor will be shipped to Singapore or Suzhou, China for testing, marking and packing. After the testing, marking, and packing operations are completed, the processors can be shipped directly to customers or to an assembler, who will pack them into trays. In an alternative processing procedure, the cut die will be shipped from Malaysia to Shanghai, China where the chip capacitor and lid are attached. Then the chips are shipped to Suzhou, China or Singapore for testing, marking and packing. After that processing is completed, the chips can be shipped directly to customers or to an assembler who will pack them into trays.

                  There are other instances when the AMD has its wafers diffused in Taiwan or Japan. When the wafers are diffused in Taiwan, they are cut and the chip capacitors and lids are attached in either Taiwan or Korea. Under this process, AMD believes that the country of origin of the semiconductor chips is either Taiwan or Korea. In the situation when the wafers are diffused in Japan, they will be shipped to Taiwan, where they are cut and the chip capacitors are attached. Under this process, AMD believes the origin of the semiconductor chips to be Taiwan.

                  AMD’s semiconductor devices can be imported into the United States either packed in trays or in retail boxes. For sale to the manufacturers of computer equipment or electronic devices, the semiconductors are imported in trays. Currently, the semiconductors are marked with the country of origin as “Assembled in Malaysia”, “Assembled in China”, “Assembled in Taiwan” or “Assembled in Korea” whichever applies.
                  He mentions a lot of testing done even before the chip is encapsulated, no doubt a final testing is also done, if anything to check the encapsulation process.

                  Also very important: MOST of the products are shipped directly to OEM factories, who will NOT accept the least problems because they would cause them huge losses ... a 15 cent part can kill a $300 product, and they will not perform component level repair, not with robotic fabrication, they will junk the bad board and get a new one from the line.

                  Simply there is no room for bad parts,period.

                  We, as individual users, benefit from the incredible quality process demanded by huge factories.

                  Now counterfeits are something else.

                  Nobody will fake a TL072, but obsolete out of production parts such as TDA1514 or many Sanken modules are an entirely different game.
                  Even recently disappeared (less than 1 year ago) TDA2050 is being substituted by relabelled well made but smaller die TDA2030 , still in production, which fail under stress.
                  Juan Manuel Fahey

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                  • #10
                    Be that as it may, I bought 2 x TL074 and 3 x TLO72 from the local electronics store (JayCar) 2 weeks ago, and one of the 074s and one of the 072s weren't working. And all I did was transfer them from the foil packaging to the DIP panel mount sockets that I had installed on the main board after I took the old chips off the board. (The board was completely charge-neutral for all intents and purposes). Seems they were duds off the shelf to me.
                    Building a better world (one tube amp at a time)

                    "I have never had to invoke a formula to fight oscillation in a guitar amp."- Enzo

                    Comment


                    • #11
                      That sucks

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                      • #12
                        Its just a PITA when you know what parts you need to finish the job, but you get home from the shop and find the new parts won't work. (I got it going eventually - with the same type of new parts, albeit ones that work)
                        Building a better world (one tube amp at a time)

                        "I have never had to invoke a formula to fight oscillation in a guitar amp."- Enzo

                        Comment


                        • #13
                          Originally posted by tubeswell View Post
                          Be that as it may, I bought 2 x TL074 and 3 x TLO72 from the local electronics store (JayCar) 2 weeks ago, and one of the 074s and one of the 072s weren't working. And all I did was transfer them from the foil packaging to the DIP panel mount sockets that I had installed on the main board after I took the old chips off the board. (The board was completely charge-neutral for all intents and purposes). Seems they were duds off the shelf to me.
                          With due respect, I suspect someting in your still unrepaired board is/was killing them.

                          Think replacing fuses in a dead amp and having them blow ... will you think they sold you duds?
                          Juan Manuel Fahey

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                          • #14
                            He did get it working with other op amps (which did not fail in the amp).
                            Were they from another supplier or a different brand?
                            "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

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                            • #15
                              Different brand. And yes, the amp is fixed and working perfectly now. (there were multiple circuit failures which took iterative repair and re-testing for me to find them all - but I found them all in the end. There were definitely 2 dud opamps I bought and replaced at the end of the process.
                              Last edited by tubeswell; 04-26-2016, 04:05 AM.
                              Building a better world (one tube amp at a time)

                              "I have never had to invoke a formula to fight oscillation in a guitar amp."- Enzo

                              Comment

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