Treadmill keeps blowing varistor...HELP

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Old 04-29-14, 10:30 AM
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Treadmill keeps blowing varistor...HELP

hi
i am not an expert in electronic, i know to solder, troubleshoot small problems but this i do not know what could be the problem.
my treadmill keeps blowing the varistor, i replace the varistor, start the treadmill all ok, when i put my weight in it, varistor blows all the time, i believe that could be related with power supply but i would like to confirm, or if someone can point me in the right direction.
thanks in advance
 
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Old 04-29-14, 01:07 PM
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Welcome to the forums.

With a schematic diagram it would be a simple job to help you. I'd imagine you don't have a schematic there.

How did you know you needed a varistor ? A varistor is usually used to stabilize power.
Based on how it's used in the circuit you may be able to use a larger value part.

Have you been in contact with the manufacturer of the treadmill in relation to this problem ?
A make and model number would be helpful too.
 
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Old 04-29-14, 06:04 PM
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hi pjmax
thanks for answering
i know that is the varistor because it explodes when i put weight in treadmill, it explodes!!!
the model is Domyos TC-450, i do not have a diagram, i can do photos of everything if that helps, i live in france and do not speak french, i cannot speak with support here.
i was in domyos site and can only get the user guide that do not have nothing important for this matter.

i attached 2 photos, one you can see varistor exploded and the other the board where it is

as i said varistor only explodes when i go over the treadmill, i force the motor demanding more current i presume, if treadmill does not have weight in it, the varistor does not explode and treadmill works normally.

hope i can give you some light about my problem for that you can give some light how to repair it.
 
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Old 04-29-14, 06:59 PM
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Stand the varistor straight up and shoot me a picture each side of it.... or one pic straight down.
What is/was the part number on the varistor ?

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Old 04-29-14, 07:33 PM
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I have found a site run by crooks. EUR49 or about $75 for a schematic only is highway robbery.
 
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Old 04-30-14, 08:40 AM
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hi again pjmax
the original varistor is a S14 K300, i bought some of this that i already tested a few and all explode.
i bought S20 K300 they are bigger but never tested those.
it is my first time with varistors, they protect the circuit against surges or spikes i presume, the fuse that is right aside is always ok, this tell me that is not a kind of short circuit must be something regarding the Voltage or current that motor demands to i presume power supply when meanwhile the varistor explodes.
i really don't understand why this happens.

NOTE: yehh i was in that site too with all kind of manuals, but i presumed big scam, because when something exists i always find some sites and not only one.in fact what you pay is for that the company go find the manual for you, that means that you lose your money.
 
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Old 04-30-14, 12:39 PM
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Right.... you don't have a short circuit. The varistor is supposed to limit an incoming rush or surge of power so that it doesn't get to the electronics. I looked at the specs on the S-20's...... they should work fine. Give them a try.... you won't hurt the treadmill.
 
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Old 04-30-14, 01:46 PM
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i finished testing 20k blows the same way, the problem comes from another piece.
when you mount in the treadmill, the motor demands current Amp right? voltage should be the same all the time i think, why after mounting the varistor blows, when this varistor goes to 300v for the specs, can the problem comes from the power supply?
if yes how can i test it?

i made photos of the other small board and the power supplys, there in one piece that i think is the power supply control the one that say powertec,
the second photo that have the small board is where i connect the motor to rise the treadmill, as a moron i forget to test only this motor to see if the varistor blows, but tomorrow i will do it.
can you tell me how can i test this powertec piece using the multimeter? what should i expect about the values.
 
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Old 04-30-14, 02:02 PM
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That varistor is rated for 423Vac max @ 8KA DISC 20MM

The varistor connects between the AC and the power supply..... I think, as I don't have a schematic.

See if you can shoot me a picture of just the varistor area. I need to see all the board markings.
 
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Old 04-30-14, 02:28 PM
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here the photos you asked for

before varistor connects power supply
 
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Old 04-30-14, 05:59 PM
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Thanks for the pics.

How old is this treadmill ?
Have you always owned it and did the problem just start now ?
What is the size of that glass fuse on the board ?

The varistor appears to be connected in series with the 240vac supply which means all the current the unit needs flows thru that part. If the unit was drawing to much operating current it should blow the fuse. I'm trying to figure out why, now, the varistor is not holding up.
Is S14 K300 the original part number that was in there ?
 
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Old 05-05-14, 05:22 PM
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hi pjmax
sorry for late reply but i was away from home
the treadmill should have 6 or 7 years, always worked perfect, never changed anything in it, till last month when she stoped working, i had opened it and only found out the varistor damaged, i had luck that part number was still possible to read and it was a S14K300.
i have many electronic material, but not varistors thats why i ordered the same ones and some others the S20 and smaller too.
both explode, i will try maybe tomorrow another test that is, put another S20 and instead of using the motor that power mat i will use the motor(more an actuator) used to raise the treadmill to see if explodes the varistor, after results i give you some info.
if you think that some kind of reading (measurements) will help i can do it, you just need to tell me what i should read.
again thanks in advance for your help, i would love to repair this treadmill because my wife already tested many other models but she prefers this one and i cannot find it in the market anymore, and i do not want to buy a second hand one too.
i think this should be something simple but i do not know from where to start
right now i have 3 S14 and 4 S20 in stock, i can do some testings with them, because if i need to order its 15 days to arrive.

Edit: i forgot the fuse, its a 4A250V and the size of the fuse is 2cmm

Edit 2: i quickly have soldered a S20 and tested the treadmill, the actuator only rises if treadmill motor is running, i started treadmill motor, and tweak the actuator up and down all ok treadmill speed motor goes up and down too, never have putted my weight in the treadmill, and after a minute - or + varistor explodes, this was my first time i tested it running without weight in it but the problem occurs anyway, wtf could this be?
 

Last edited by Estrika Lhado; 05-05-14 at 05:54 PM.
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Old 05-05-14, 09:01 PM
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Try removing the varistor and see if unit operates.

I've been looking over a bunch of schematics from other companies and the varistor is only used as a surge protection device and will run without it.
 
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Old 05-05-14, 10:03 PM
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but probably i will burn other components dont you think?
and without the varistor it does not power on

Note: i forgot to tell you, but when varistor explodes the electric switch of my house goes off too, is this normal
 

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Old 05-05-14, 11:20 PM
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What electric switch goes off...... the circuit breaker ?

Every other schematic I've looked at has the varistor across the incoming line. In that application it's used strictly as a surge protector which is what it was designed for. The treadmill would run but without incoming line surge protection.

Yours is in series with the incoming line (if the unit is dead without it in place) and that means all the current your tread mill is using is being drawn thru the varistor. If the varistor is burning then logic tells us that your treadmill is drawing too much power.

Without a schematic of your unit I don't know if I can be of much more help.
 
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Old 05-05-14, 11:25 PM
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i tested without varistor, the treadmill worked but for some miliseconds it stop working and started again, like if the black boxes in the photo i do not know the name in english have sented order to stop and start, it worked with those kind freezes for some minutes but them all stop, i have power, led is not anymore green in board and i have error E1 in display, i go to work now, later i will remove the pcb and take a look at it.
 
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Old 11-20-15, 11:02 AM
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I had the same issue. Just change the big capacitor (470 uF, 400v) and put a new varistor. The inner thin sheet into the capacitor breaks because of material fatigue due to vibrations. You can open the capacitor and see it. It's very curious.

Hope this helps.
 
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Old 10-28-16, 03:15 PM
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Same problem here. Replacing the varistor and the 470uF did the trick. If you try without varistor then the big transistor TOHSIBA TO-3PL GT60M303 blows too.
 
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Old 10-28-16, 04:23 PM
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Welcome to the forums and thanks for the additional information.

Without actually seeing a schematic on the circuit I can't comment on the capacitor to varistor relationship. The cap should have no effect on the varistor but it can affect the treadmill circuitry greatly.
 
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Old 10-29-16, 08:22 AM
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Interesting. I currently do design work in switch mode power supplies, though not for treadmills.

Let me try to explain about many of these parts you have in front of you on this PCB.
There looks to be two different types of varistors in your circuit that have much different purposes. The blue one that keeps blowing up is a MOV type, "20" in the part no refers to its diameter, and the "300" is its rated AC voltage maximum. This is a high Ohm device, unless the trip voltage is exceeded. Its purpose is to limit Line to Neutral surge voltage damage from lightning and other sources. There is also a yellow "x" capacitor across it the dampens high frequency RF emissions from the switching supply.

There is a green one in there, that appears to feed the bridge rectifier. It is a current surge limiter and is a low ohm device. It gets even lower in Ohms as it heats up. Not a MOV and its purpose is to pass a test that limits surge current at power up.

The large electrolytic capacitor at 400V dc, 470uF is necessary to convert the pulsating DC waveform from the rectifier to a smoother DC for use by the motor drive circuit. If it opens up, which they can do after many years, high voltage spikes may result. In this case, these voltage spikes are now appearing across the MOV and causing it to conduct, overheat, and destroy it. More of this and the power FET driving the isolation transformer will blow due to overvoltage.

I see the PCB layout suggests different wiring for 110 vs 220 volts (its naming, not mine).
Most of these type switchers can accommodate 100 to 240V ac without any wiring change, so that is a curious thing, that I can't explain without more careful inspection.
 
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Old 10-29-16, 09:27 AM
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This is a 2-1/2 year old thread that someone resurrected. The OP has not been back since.
 
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