Troubleshoot And Repair This ADCOM GFP-1A Stereo Preamp

Troubleshoot And Repair This ADCOM GFP-1A Stereo Preamp - Part 1

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Follow along as Erik troubleshoots and repairs this ADCOM GFP-1A stereo preamplifier. A quick overview of the preamp is discussed including the unusual CX noise reduction feature. Then a look at the schematic followed by troubleshooting process to find the fault.
Part 2 video link • Troubleshoot And Repai...
#adcom #electronicsrepair #preamplifier

Пікірлер: 18

@manosmul6827 7 ай бұрын

Complete novice here. First time my brain has not been scrambled by this type of video. Thank you for the clear and reasoned presentation.

@EriksElectronicsWorkbench 7 ай бұрын

Thanks for watching and the compliment on the video.

@xyloeye 6 ай бұрын

This is the best troubleshooting video I've seen since Mark Zacharias was doing them. Thanks for taking the time to record it.

@EriksElectronicsWorkbench 6 ай бұрын

Thanks for the nice compliment! Happy to know you enjoyed the video.

@poormanselectronicsbench2021 7 ай бұрын

@ 16:05 ,Not a lot of people have a meter that can read out to over 100M Ohms, which is a nice function on the Fluke 289 ( I am jelly) , BUT, some older Flukes even some of the "80XX" side push button handheld, and bench models, a few of the higher end Brymen and a few Agilent models have a nS , or "Nanosiemens" function that can find resistance faults to over 10G Ohms or higher ( some up to 100G Ohms, or 0.01nS) and measure it in a conductance value, The same function setting also can be used to check for leakage in poly/paper/mica capacitors using a safe-low voltage, and gives a quantitative measurement. @ 34:50 You also have to keep in mind that something past that wiper may be dragging the signal to ground / chassis common as well, but I guess we will have to wait for part 2 for more info.

@EriksElectronicsWorkbench 7 ай бұрын

The Fluke 289 is a great DMM, been very pleased with it! For the potentiometer, I noticed that if the wiper was turned to the side of the resistance where the signal enters it did not pull the signal down so I figured no short to ground on the wiper circuit.

@mjg263 6 ай бұрын

Great troubleshooting video! I seem to recall reading that Adcom had some problems with defective balance pots in these, I think I read about it on Audiokarma years ago. I love the original Adcom gear and still use it to this day. I still have my GFA-2 power amp in its original box, that was my first piece of Adcom gear. Currently use a GFA-555 PRO driven by a GFP-565 preamp which I’m more than happy with, I stopped looking after trying that combination. Truthfully the GFP-555 preamp was good enough but the 565 is a little nicer (especially the phono section).

@EriksElectronicsWorkbench 6 ай бұрын

Thank you! That is interesting about the balance pot and fits with this situation. It shouldn't have failed, no overload, not worn out, etc. Your ADCOM items are very nice. I have several ADCOM units too and enjoy them, the GFA-555II being a favorite.

@nicksundby 7 ай бұрын

Really good video

@EriksElectronicsWorkbench 7 ай бұрын

Thank you!

@mohimadvani6425 6 ай бұрын

waiting for part 2😊

@EriksElectronicsWorkbench 6 ай бұрын

working on it :)

@mdzacharias 7 ай бұрын

The tops of those caps are not connected directly to either lead. You're measuring leakage.

@EriksElectronicsWorkbench 7 ай бұрын

The charge that builds up is still a shock hazard though. Also not a harmless "ghost voltage" as a low impedance mode on the DMM won't immediately eliminate the voltage.

@mdzacharias 7 ай бұрын

@@EriksElectronicsWorkbench I was suggesting it's not a good test point for troubleshooting or verifying proper power supply output.

@EriksElectronicsWorkbench 7 ай бұрын

@@mdzacharias Yes agree, the top of the capacitors are not a test point. I mentioned the voltage (and measured it) on the capacitor tops just as a matter of safety issue.

@AndrewTa530 Ай бұрын

You only had chan 1 selected on your scope

@EriksElectronicsWorkbench Ай бұрын

Both channels were turned on and active. That is shown by both channel traces being displayed. The reason only the Ch 1 indicator light was on is that shows which channel the vertical controls will affect. Notice the scope does not have two sets of vertical controls on the panel.