Stryker SR-497HPC what a mess!

[brandon7861]

Sounds right, C212 is listed as M104 on the schematic, and I remember those green 104's being on the larger side.

Guessing here. I wonder if they added that cap to extend the higher range of frequencies that can pass around the regulator. If I assume an inch of trace and cap lead between the cap and transistor (about 20nH), the self-resonant frequency would be in the 3.5MHz area and going inductive above that. A ceramic chip of lower value might help keep RF off the regulator, if any were to leak back past the final chokes.

 

[Cable Guy]

Sounds right, C212 is listed as M104 on the schematic, and I remember those green 104's being on the larger side.

Guessing here. I wonder if they added that cap to extend the higher range of frequencies that can pass around the regulator. If I assume an inch of trace and cap lead between the cap and transistor (about 20nH), the self-resonant frequency would be in the 3.5MHz area and going inductive above that. A ceramic chip of lower value might help keep RF off the regulator, if any were to leak back past the final chokes.

Given the additional shielding and intentional stage gain reduction, I would agree with you. Seems they put it all together and realized they had a problem. What value would you guess?

 

[brandon7861]

I would try 1n. That would be about 6ohm at 27MHz and resonate at 35MHz with the same lead length.

 

[Cable Guy]

I would try 1n. That would be about 6ohm at 27MHz and resonate at 35MHz with the same lead length.

Thanks, I will try it out in the morning. I haven't noticed any oscillations but better safe than sorry.

 

[brandon7861]

I doubt it would oscillate, but it might affect the modulation waveform a little. It might not even be necessary, and I could be wrong about the purpose.

I guess I would scope the regulator with a clean tone going in before doing anything else since it seems to be working.