Dynaco FM3 Cap Board Kit – $79.00 CAD
Scroll to the bottom if you would like to download the assembly manual as a PDF.
This kit for the Dynaco FM3 replaces the silver can capacitor, C32 and resistors R36, R37 & R38 which improve the B+ power filtering.
These are all high quality components ordered from Digi-Key not some sketchy overseas seller. The electrolytic capacitors are Nichicon UCS with a rating of 10K hrs. @ 105 and a ripple current rating of 225mA @ 120. The resistors are Bourns and Vishay. No low quality bulk components are used.
Although this is a fairly easy swap this is not a beginners kit. There is high voltage involved, do not attempt this as your first upgrade unless you absolutely know what you are doing.
Assembly
FM3 Capacitor board assembly and installation:
This board replaces the silver can capacitor, C32 and resistors R36, R37 & R38 which provide the B+ power filtering.
Parts List:
For the 500 Ohm 5 watt you can use the big rectangle ceramic wire wound types or regular wire wound resistors. For the 470R you can use a 1W or 2W wire wound type. You can reuse the original resistors if they do not look burnt and test within spec. Solder all three of the resistors, so they have a small gap between them and the PCB. This allows airflow and prevents the heating and cooling cycles from stressing the solder joints.
Solder R3 first, R1 & R2 second and then all the capacitors. Make extra sure you have the capacitors in the correct orientation, the negatives should all face the same way. If you put one in backwards you are going to have a firecracker when you hit the switch.
Power Supply Original Schematic
FM3 bottom picture
Once the cap board is assembled make sure the FM3 is unplugged and take the cage and bottom off by removing the 4 flat head screws on the sides. Remove the 6V4/EZ80 tube from socket V-9 and put it somewhere safe.
****HIGH VOLTAGE WARNING****
This is not really an absolute beginner project, so I assume you are comfortable working with high voltage and know how to discharge capacitors. If you do not, please pay someone to do this upgrade for you.
Flip the unit upside down so you have the same view as above. Discharge all 4 sections of C32 and unsolder all the wires and resistors attached to it, keeping track of what lug number the wires were attached to.
Lug 1 = Pin 3 of Tube V-9 (6V4)
Lug 3 = Eyelet 22 & 27 of PC-8
Lug 4 = Eyelet 12 of PC-7, 34 of PC-8 & 87 of PC-12
Ground Lug = Lug 3 of the terminal strip & Red/Yellow transformer wire
Now that you have everything unsoldered, twist the metal tabs, so the cap drops out. You may have to wiggle it back and forth a bit from the topside. Once out you can get to installing the new cap board. Undo the small nuts and remove the bolts holding in the V-9 tube socket. Replace the bolts with the standoffs and put the nuts back on. Test fit the cap board on the topside to make sure the standoffs align to the holes in the PCB on either side of the half moon cutout and screw it down with the two screws.
While the PCB is test fitted, run the wires that were attached to the lugs through the hole where the C32 capacitor was and check if they can reach the holes on the cap board. If they are not long enough you can either extend them with some wire and shrink tubing for insulation or just solder on longer wires. Another option is to put in a 4-lug terminal strip and use one lug for each of the connection groups and run short wires to the PCB. If you use a lug strip one of the lugs is usually grounded, make sure you only use that lug for the ground connections.
Once you have all the wires long enough to reach the PCB, unscrew the PCB from the standoffs so you can insert the wires into the holes to be soldered. Solder the wires into the holes as follows:
Pin 3 of Tube V-9 (6V4) to the PCB hole labeled “To 6V4 Pin 3”
Eyelet 22 & 27 of PC-8 to PCB hole labeled “B+ #1”
Eyelet 12 of PC-7, 34 of PC-8 & 87 of PC-12 to PCB hole labeled “B+ #2”
Lug 3 of the terminal strip & Red/Yellow transformer wire to PCB hole labeled “GND”
When all the wires are soldered you can screw the PCB back down to the stand offs and reinsert the 6V4 tube. Double check all your wires are going to the right places and that all your connections are solid before you go for that switch.
Once warmed up you can test the voltages. The voltage on B+ #1 should be around 225V and B+ #2 around 220V.