PC 7518 acting up

[Michael Gibbons]

Mounted in the table, the motor hums for a few seconds after the power button is pushed then it winds up. Is it possiblly that the brushes are dirty or corroded or something else? I don't use it very often. If I take it apart, would using scotchbrite work or should I just order new brushes? The motor probably has less than an hour and a half use in 12 years.

[Bruce Wrenn]

The capacitors in the control board have bit the dust. Very common problem. PC uses a $5 control board, but sells replacements for over $100. A google search most likely will turn up both values and how to do it replacement of caps.

[Larry Edgerton]

If it is just seeing table use you can wire the speed control out of the circuit. I have several that are wired that way, not an issue for me.

[Mike Gresham]

This was posted several years ago. However, I can't find the actual post now and can't remember who posted it. It is for a 7529, but maybe it will help.

"I have had a dead PC7529 sitting on my bench for years. Finally decided to try to fix it. I came across this thread. It was the key to a quick 1 hour fix.

I checked the switches, potentiometer, and brushes. All okay. So then suspected one or both of the electrolytic capacitors were bad, as per this thread. I desoldered the one in the upper corner of the control board, as seen in an earlier post. I had no direct replacement and am impatient (once I start on something [IMG]file:///C:\Users\Mike\AppData\Local\Temp\msohtmlclip1\01\c lip_image001.gif[/IMG]). I had some electrolytics sitting around on my electronic bench. I used a small 47 mF, 50V cap with radial leads. I draped the cap over the IC and surface soldered the leads. Thought about doing the other one in the middle of the board, but remembered the keep-it-simple rule. Quickly buttoned it up and tried the power. Worked! Speed control functions normally also.

Comments: These caps are in a DC control circuit. They are not connected to 120VAC line current. The original unit was rated for 35V. Since many seem to go bad (early), it may help to overrate the replacement as I did (with 50V unit). It can't hurt. Second, I did not have a 22 mF cap and used a 47 mF. Electrolytics are used to smooth out DC voltages by draining superposed "ripple" (AC) voltages from the rectifier to ground. A large capacitance makes for less ripple. Hence I expected it was okay to overrate here also. And that seems to be the case.

However, as with anything electronic and DIY, you are on your own and best send it for professional repair if unsure of what you are doing."