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I am getting 4.6 volts on tap 6 and it is not adjustable by R18. I am certain that all components are in correctly, I am looking to get an output of -1.6 to +1.6v as in the instructions, Any suggestions I am stuck on this step.
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You can monitor TP3 to check that the adjustment is having any effect. Then look at TP4 with the coil disconnected. Note - in the article it says, "Leave the coil L1 off for now".Originally posted by douglas View Post -
I seem to remember mine having a narrow adjustment range, I had a 20 turn cermet pot for R18 and nothing seemed to change on TP6 with several turns in either direction, however keep turning as I did eventually get adjustment but it happened very quick within a turn or soComment
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Ok well it is working now.
Sorry fellas, I meant that on IC 6 I am getting proper voltages on pin 7 and pin 4.
I am on page 8 of the instructions right colom half way down.
When I test Tap 4 which is connected to pin 6, I get the -.4 volts and it adjusts up to +1.6 v. Which is great but if I leave the power on tap 4 voltage begins to climb up to 4.3 volts.
I don't understrand why. There is no coil attatched and R5 is removed still from previous step.
I do have c 10 installed as well. Thanks for your suggestions.Comment
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what voltage you have on middle pin of R18 in its utmost positions?
you have clear to see approx -3 and +3V. begin from this.Comment
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Douglas,
C27 is a noise filter cap that has about a 6-7 second time constant, so you need to make adjustments to R18 rather slowly. If you over-adjust and wait a few seconds, you will see TP4 slowly go out-of-range. You can lift out C27 for making the adjustment if you like, then it will be instantaneous.
- CarlComment
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HH is coming along well I made the adjustment and it worked out per instructions.
I an now getting a tone on the audio that is variable in pitch by adjusting either/or r3, R3.
Coil is made from instructions and is firing.
Using oscilloscope:
Output of preamp looks good (like FIG 24. in instructions)
I am getting a good trace for TP7 as well.
the problem is no trace on TP6 at all.
components around IC 11 are correct. and Q8 has been replaced for good measure.
I am using a 74hc221
Theshold or auto track makes no change in monotone coming out of speaker.
I think I may need a new 74hc221?
Any suggestions?Comment
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If you have an output at TP6, but the signal at TP7 looks ok, then I would suspect Q9 is either faulty or incorrectly inserted. Presumably there is a correct signal at N2 (pin 5 of IC11b)? Otherwise IC12 would never be triggered, and consequently there would be no output at TP7 (which you say is not the case). Try looking at pin 12 IC11b to confirm that the main sample pulse is present.Comment
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I turned out to be a connection and I resoldered and the baord is working.... I only need to get the tuning down as I am unfamiliar with PI detectors. I will have to go back over the instructions and make some re-adjustments.
Thanks for the help.Comment
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signal form at TP4
Using my own program for digital processing of pulse inductiom MD I get the following form of signal (seee as attachments) At this image is visible resonanz of coilComment
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