Silent HVM

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Schlumpfhut
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Silent HVM

Post by Schlumpfhut »

Merry Christmas everyone

i spent Christmas Eve building a HVM and sadly it does not work as expected :eek:
Using my Scope i was able to verify that an incoming signal passes U7 and is distributed to all Filter Cells.
Problem is that half the filter cells do not seem to reccive anything. The scope shows either nothing or only partially on input or output pins of the opamps.

I have triplechecked the soldering and everything checks out fine regarding of shorts or cold joints.

Does anyone has an idea where to look from here on?
Thanks very much in advance
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Synthbuilder
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Re: Silent HVM

Post by Synthbuilder »

Happy Christmas! :party:
Schlumpfhut wrote: Sat Dec 25, 2021 3:26 amDoes anyone has an idea where to look from here on?
Two things come to mind.

Check that RN1 is around the right way.

There's a lot of normalised connections on this module's input sockets. Check that the input signal is getting to the output pins of U5 and U6 when the appropriate pots are turned up. eg. Female 4' Upper (F4U) should be on pin 7 U6. The pots control the input levels to the filter cells and not the output levels directly.

Tony
Schlumpfhut
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Re: Silent HVM

Post by Schlumpfhut »

Synthbuilder wrote: Sat Dec 25, 2021 4:20 am Check that RN1 is around the right way.
I checked and i checked again. RN1 is around the right way. The dotted pin sits in the square hole as described in the Builder's Guide.
Synthbuilder wrote: Sat Dec 25, 2021 4:20 am There's a lot of normalised connections on this module's input sockets. Check that the input signal is getting to the output pins of U5 and U6 when the appropriate pots are turned up. eg. Female 4' Upper (F4U) should be on pin 7 U6. The pots control the input levels to the filter cells and not the output levels directly.
I checked this and found that only the F4U socket does not reccive anything at the NC pin. Further probing showed that the output of U7 does go past R38, R39 and R59. The signal is clearly visible on one end of the resistors but when i probe the solderside of either of the three i see nothing on the scope.
May it be that soldering the board connetor somehow damaged the resistors? The original values are correct (470R and 1K)
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Synthbuilder
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Re: Silent HVM

Post by Synthbuilder »

Schlumpfhut wrote: Sat Dec 25, 2021 6:22 am The signal is clearly visible on one end of the resistors but when i probe the solderside of either of the three i see nothing on the scope.
Is the signal visible at both ends of all three resistors on the topside of the board? If it is, but not getting to the NC lugs of the input sockets then that would suggest a problem with the wiring. If there is no signal there, that suggests a short to 0V. This is easy to verify; with the power off, check the resistance between the end of the affected resistor and 0V (pin 2 of the PSU power header). If it's 0R or something very low, you have a short. Check that you haven't swapped the NC lug with the ground lug of the sockets. It may be worth unplugging UPR and LWR and checking if the short is still there.
Schlumpfhut
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Re: Silent HVM

Post by Schlumpfhut »

I have checked as you suggested and everything is fine there.
My main suspect is by now the 8-pin connector. According to the schematics pin7 goes to ground and since pin 6 is the only one not working the short might been beetween the connector and the PCB.
To check i will need to re-set up my workbench and desolder the connector. Might take i day but i will report back once i am finished
Schlumpfhut
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Re: Silent HVM

Post by Schlumpfhut »

Yesterday i replaced the connector and now the complete module is silent again.
I have decided to shelve it along some notes for the time being and come back to it at a later date.

Thank you very much Tony for your time and effort.
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