Is my capacitor dead?

[metalsun]

My treadmill stoped working and I suspect it's due to a faulty motor controller board. There is one large 30mmx45mm 390uF 400v 85c capacitor that looks slightly swollen on top, but how can I tell if it's no good? I don't have any testing equipment. I hope the fault is the capacitor as it would be cheaper to replace rather than the whole board.

Kind regards,
tommy

 

[metalsun]

Hi, Thanks for your help

There are two components that are sandwiched between aluminum heat sinks - not sure what you call them, but they must get hot and the heat sinks spread the heat, anyway one was a bit loose so I soldered it back to the board, maybe that was the underlying problem? I will replace the capacitor, luckily for me I can get the replacement cap from ebay with the same specs.

 

[#1supertech]

your TM shutdown problem

metalsun,

Sounds like you have a common heatsink on the PWM board that has either POWER MOSFETS on it, or else a combination of solid state devices on it that are in a TO type packaging.

Most jogging/running TM's that I've worked on have 2 bigger PCB's minimum in the belt drive "motor compartment". One is the CPU Logic Brd, and the other usually being the Drive PWM Brd.

A good digital pix or 2 of the PCB showing the problem area(s) surely would help here (suspected bad CAP pix included). If you take a couple digital Jpeg pix and post them make sure you shoot the Jpegs around 250kb in size and no bigger!! That equates to a camera setting of (SQ1 at the 1280 x 960 NORMAL) mode setting. Thx in advance if you can accommodate me here!

I've repaired several TM's in my days, and it always seems to be the same "several components" located on the PWM board near the POWER OUT components that are usually all heatsinked together on 1 common AL heatsink strip. Usually there are 4 TO type packaged devices together on that heatsink - usually! Next to that heatsink usually are a couple HEAVY WATTAGE SURGE resistors in the 5 to 10 watt range that usually will go bad as well. One might be a 1200 to 2400 ohm 5 to 7 watt rated (ceramic encased type white in color), and one might be around 220 ohm 1 to 2 watt rated (blue or black in color) or there abouts wattage wise.

Sometimes you can visually tell they are bad just by looking at them if they are a burnt looking dark brown to black color, or else if there's a burnt like darkened PCB underneath where they are mounted on the PCB itself. That's always a bad sign as well.

Most likely they will need to be R&R'd just to accurately measure them (ohm out that is). If they are even out of tolerance Check its stamped tolerance % rating, and if it's out of spec by any degree change it out with the same exact value and wattage rating! You can always go higher on the wattage rating just as long as the resistor leads fits through the existing PCB mounting holes.

In checking the PCB components whether they are diodes, resistors, or just basic diode junction transistors ALWAYS USE a good quality DVM to perform those tests (or a cap testing meter), and NOT by using an older analog type multi-meter - such as what I believe you are using unless I'm guessing wrong here? I just don't trust the older analog meters anymore - those that I too grew up with when I first started out eons ago now!

In troubleshooting (T/S) your (any) PCB there - always desolder only 1 lead from any axial 2-lead passive component (unless it's a multi-pin/lead passive device package then remove it entirely). Where the component IS a typical 3-pin active device transistor, SCR, TRIAC, or say (MOS)FET in nature - then definitely desolder the related part totally - even if it's heatsinked to the PCB, as otherwise you will never DVM check it out properly. Unless you definitely KNOW that the latter is true then there's no need to remove it (ie: burnt or cracked casing, etc).

I've had to do the latter with higher priced TM's even though the related Power Resistors on the PWM motor drive boards were at fault to begin with. Just because a high wattage SURGE resistor "looks good" on the outside doesn’t mean it "IS GOOD" inside. I've seen them go out of spec by as much as 50-60% of rated value and tolerance, and even partially OPEN UP when superheated - or act as an OPEN in the SURGE or feedback circuit - thus sending the control board into shutdown!!

Rarely will a 3/4 turn or single turn TRIM POT go bad unless it's a cheaply made variety to start with. I've seen the ones like you have there - on your PCB - have wiper intermittents - as from contact age, but it's rare. Always look for the obvious first!

Tapping the side of the POT slightly while measuring it should show no signs of value wander! If it jumps then its SHOT - replace it. Try and measure its "set point" out of circuit first, and replace it with a 10-turn POT instead - so a more accurate setting can be made after the R&R.

I see that you did find a loose heatsinked TO packaged solid state device that had to be resoldered. That was not a good sign at all, and either vibration caused that to happen or a combination of heat and vibration?? In either case my guess is that possibly you have a bad Surge resistor there that caused that excessive heat to loosen the solder on that TO device.

Can you post a part # for that loose heatsinked device? That and a good digital pix would help me to nail it down for you. Thx in advance if you can!

If you really suspect that one large 30mmx45mm 390uF 400v 85c capacitor then it will need to be taken out (desoldered) and CAP meter measured for proper value. I take it that it's soldered in place? If it's indeed good it probably has a healthy stored voltage on it so be careful taking it out to measure it properly, unless it had a bleed-down resistor in it's circuit to discharge it once the TM is shutdown. The latter usually being the case. Hopefully you have a good stand alone CAP meter, or else your quality DVM has a built in one by chance? I have a separate B&K CAP meter myself. I usually don't have to measure a lot of bad caps these days, and my higher ended precision Wavetek DVM does me just fine without that added CAP feature!

Other then that - without seeing a couple of posted "clear" (not blurry) digital Jpegs I don't know what else to tell you - as I can't see the PCB there.

Best regards,

Frank

 

[mvs sarma]

My treadmill stoped working and I suspect it's due to a faulty motor controller board. There is one large 30mmx45mm 390uF 400v 85c capacitor that looks slightly swollen on top, but how can I tell if it's no good? I don't have any testing equipment. I hope the fault is the capacitor as it would be cheaper to replace rather than the whole board.

Kind regards,
tommy

is it oil capacitor, if so it wont be of such high value
is it electrolytic
if so, top bulge definitely indicated almost end of life. if the equipment is under warranty, you may ask service, otherwise just get one and replace

 

[metalsun]

Thanks for the info frank.

After my last post I receved a new CAP and a digital multimeter. I found the transformer to be bad as I couldn't get a continuinty beeb/reading from the input wires using my multimeter, the output wires are ok. The transformer input is 230v AC duel out put is 10v and 17v AC. So that sucks because I can't fix the transformer due to the iron core lockng the windings inside. They need to be custom made to the same specs, so I can't just buy one off ebay like I did with the CAP. But I'm happy with my findings using the multimeter because I had my suspicions with the transformer. The board looks clean, no sings of burnt parts.

As for a pic, this is the board for my reebok i-run treadmill, not my own picture sorry. It is a very simple board with not many components.

https://cgi.ebay.co.uk/ws/eBayISAPI.dll?VISuperSize&item=370266001953