Spectrasonics 101 Power Issue

pmercer · Jun 4, 2020

Third time racking these up, first time using the JLM power plant. Having a very strange issue where when I have the cards inserted, voltage drops from 24V to 12V. I tested the supply and set the voltage correctly with the trim pot to 24V (and 48V for phantom), and when the cards aren’t in the edge connectors, the connect there tests perfectly at 24V. But as soon as I slide the cards in, the voltage on the connector and back at the supply on the 24V rail drops to 12V. Continuity tested, all my grounds are connected and are separated from the audio and power paths...any ideas? Thanks!

gridcurrent · Jun 4, 2020

pmercer said:
Continuity tested, all my grounds are connected and are separated from the audio and power paths...any ideas?

continuity from "E" to "F" ?
shorted output transistors ?

pmercer · Jun 4, 2020

gridcurrent said:
continuity from "E" to "F" ?
shorted output transistors ?

Do you mean the Feedback loop? No continuity there, I have the gain on a stepped switch with 4 series 10K resistors...

pucho812 · Jun 4, 2020

voltage drops under load. Possible power supply is not robust enough to handle the load but highly unlikely. More likely that there is a problem on one or all of the cards. You can try and do a single card at a time, and see if one or all cause this issue. I believe the schematic is readily available. Should be easy to find the culprit.