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01/16/06 01:06
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 		 #107444 - How do adjust the cap trimmers?
Responding to: ???'s previous message
To obtain optimum results, the cap trimmers of the following dampening network must be adjusted properly. This is done by the help of a good square wave of about 500Hz, or so. You can use the output of a 74HCMOS gate, for instance. Adjust all the trimmers, so that an ideal square wave can be seen on screen, means a square wave neither showing overshots nor rounded edges. Don't worry, the adjustment is really simple, the only thing you need is a special isolated (correctly spoken metal free) screw driver, manufactured for such adjusting tasks. You can also carve it from a wooden toothpick by yourself...



1. Choose 1:1 dampening of probe, choose 1:1 dampening of scope. Adjust probe for ideal square wave.

2. Choose 1:1 dampening of probe, choose 10:1 dampening of scope. Adjust cap trimmer across 909k resistor for ideal square.

3. Choose 10:1 dampening of probe, choose 10:1 dampening of scope. Adjust cap trimmer at 909k resistor to ground for ideal square wave.

4. Choose 1:1 dampening of probe, choose 100:1 dampening of scope. Adjust cap trimmer across 1M resistor for ideal square.

5. Choose 10:1 dampening of probe, choose 100:1 dampening of scope. Adjust cap trimmer at 1M resistor to ground for ideal square wave.

Take care, that you don't introduce stray capacitance by your hands during the calibration. So, close the enclosure and verify the correctness of calibration after the adjustment.

Kai


List of 87 messages in thread
TopicAuthorDate
20Mhz Analog Input of a DSO            01/01/70 00:00      
   Link            01/01/70 00:00      
      why go for 20MHz            01/01/70 00:00      
         No 4 layer PCB & faster ADC available            01/01/70 00:00      
      Initial look ...            01/01/70 00:00      
         Trigger Circuit            01/01/70 00:00      
            Try of explaination            01/01/70 00:00      
               Badly drawn            01/01/70 00:00      
               Trigger and Amp            01/01/70 00:00      
                  Take care...            01/01/70 00:00      
                     Speed            01/01/70 00:00      
                        Like This ?            01/01/70 00:00      
                           Just wait...            01/01/70 00:00      
                              so what do they do there ?            01/01/70 00:00      
                                 Direct Digital synthesis            01/01/70 00:00      
                                    I just can think about one benefit            01/01/70 00:00      
                     Searching...            01/01/70 00:00      
                        Misinterpretation            01/01/70 00:00      
                           Proper Op-Amp            01/01/70 00:00      
                              AD844 has 50 Ohm input resistance on -            01/01/70 00:00      
                                 inverting input resistance            01/01/70 00:00      
                              specifications            01/01/70 00:00      
                                 sampling            01/01/70 00:00      
                                    Of course            01/01/70 00:00      
                                       Yes but            01/01/70 00:00      
                                          Exactly!            01/01/70 00:00      
                                 Preamp Initial Schematic            01/01/70 00:00      
                                    please resubmit the schematic in a forma            01/01/70 00:00      
                                       Real size button            01/01/70 00:00      
                                          not quite good enough            01/01/70 00:00      
                                             Higher Resolution            01/01/70 00:00      
                                       Resize            01/01/70 00:00      
                                          I do not care if it fits, I can move it            01/01/70 00:00      
                                             readable with gthumb            01/01/70 00:00      
                                             They are1N4148s            01/01/70 00:00      
                                             Problem is at your end            01/01/70 00:00      
                                                do you refer to the first submit            01/01/70 00:00      
                                                   Web Browser            01/01/70 00:00      
                                                   Both            01/01/70 00:00      
                                    Some changes needed            01/01/70 00:00      
                                       have to sleep a little ,will post later            01/01/70 00:00      
                                       I would try this            01/01/70 00:00      
                                          not an analog eagle            01/01/70 00:00      
                                             Why not            01/01/70 00:00      
                                                not objecting, just wondering            01/01/70 00:00      
                                          Updated Schematic            01/01/70 00:00      
                                             FETs            01/01/70 00:00      
                                                I remember going to the races on Thursda            01/01/70 00:00      
                                                   Yes, Nowadays they're held at friday            01/01/70 00:00      
                                             Answers            01/01/70 00:00      
                                                JFET Input good            01/01/70 00:00      
                                                   Deviations            01/01/70 00:00      
                                             Answers II            01/01/70 00:00      
                                                Corrected mistakes            01/01/70 00:00      
                                                   Answers III            01/01/70 00:00      
                                                      RE : Answers III            01/01/70 00:00      
                                                      new questions about PCB/Supply            01/01/70 00:00      
                                                         Answers IV            01/01/70 00:00      
                                                            RE : Answers IV            01/01/70 00:00      
                                          How do adjust the cap trimmers?            01/01/70 00:00      
                                             Thanks for everything            01/01/70 00:00      
                     Found these            01/01/70 00:00      
            inductance            01/01/70 00:00      
               Relays            01/01/70 00:00      
                  Reed-relay            01/01/70 00:00      
                     Reed Relays            01/01/70 00:00      
         Plays no significant role            01/01/70 00:00      
            but they are sensitive            01/01/70 00:00      
               Analog Mux            01/01/70 00:00      
                  today Philips announced this MUX            01/01/70 00:00      
                  Strac capacitance make the worse            01/01/70 00:00      
                     Sorry, stray not strac            01/01/70 00:00      
   a better aproach maybe            01/01/70 00:00      
      PLD question            01/01/70 00:00      
         Re PLD questions            01/01/70 00:00      
            link            01/01/70 00:00      
            Go for CPLD or not !            01/01/70 00:00      
               Not in that timescale            01/01/70 00:00      
                  so about 10K gates are needed ?            01/01/70 00:00      
                     part numbers            01/01/70 00:00      
                        Wow pretty expensive !            01/01/70 00:00      
                  I'll have to wait till tommorow            01/01/70 00:00      
   is this helpful?            01/01/70 00:00      
      good link            01/01/70 00:00      
   Heres a start            01/01/70 00:00      
   'must read'            01/01/70 00:00      
      What a great reference !            01/01/70 00:00      

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