High Voltage Shocker - components blown in new machine

[Douglasbell01]

I recently bought a 110v screen printer (Yudu), shipped over from The USA to The UK. Very rare in the UK. Almost no info online about repairing it (probably discontinued by the manufacturer).

The UK's 240v mains supply did not go down well, as the Yudu was plugged in excitedly without thinking about the different US/UK voltages. I've since bought a voltage converter.

Switched it on and... Pop! Spark, smell, noise. The fuse blew out, and a ZNR1 Varistor too. Maybe more. Photos attached.







Bought replacement fuses off eBay. I had to snap the fuse connector caps off, regrettably, when taking off the old fuse.

Testing a new fuse with Voltage Convertor in use: it pops. The machine's lights do come on for a second. So there's life in her yet, I hope. The varistor hasn't yet been replaced. I guess this needs to be replaced to stop the fuse blowing

Q1: Can I solder the new fuse on directly without connector caps?
Q2: My search for a ZNR1 Varistor replacement online has failed. Can you help me find a replacement? I've searched all over, including Maplin.co.uk (I'm a novice, so perhaps it is my description of the component).

Q3: Are there other components that are likely to have blown too?

My hope is to fix this cheaply, and to learn something in the process. There's no obvious place that I know of to take it to for help (in London) - so I was relieved to find this forum. The machine is bulky, so difficult to take on buses to a repair shop (if they still exist).

If there are other things I should be considering, please do share your thoughts. All help much appreciated.

[cheapie]

Re: High Voltage Shocker - components blown in new machine

The varistor's for surge protection, and it thought that the 240V was a surge. It blew the fuse to protect the machine. You can leave it out if you use a surge protector. Judging by the lights, I think that the varistor did its job and nothing else was killed, but you'll have to try it with no (or new) varistor and see. As for a replacement, it's just an MOV. Probably around 300V, but I believe that the tolerances can be very large, resulting in it shorting (which it [/i]is[/i] supposed to do) at 240V.

[budm]

Re: High Voltage Shocker - components blown in new machine

The original MOV was probably 150V. So if you are going to use the step down transformer to operate this unit, then you should use the 150V MOV. Do you know the diameter of the old MOV?

[goontron]

Re: High Voltage Shocker - components blown in new machine

clean the bloody soot off the thing before messing with it more and i have found one that might work (same rating) but without the diameter i can't gurantee http://uk.farnell.com/littelfuse/tmo...95v/dp/1680659
as for the fuse, i have soldered on a fuse without the end-caps but i destroyed 3 fuses in the process.

[PeteS in CA]

Re: High Voltage Shocker - components blown in new machine

MOVs are damaged at least a little every time they absorb a surge. When it's a large long-duration "surge" such as applying 240VAC to a P/S set for 115VAC, the damage will be a severely decreased trigger voltage, becoming shorted, or shrapnel. Sounds like the fuse limited the damage to a decreased trigger voltage. If you replace the MOV, a larger diameter part will be fine (it just means being able to handle greater surge energy) as long as you match the trigger voltage rating.

[westom]

Re: High Voltage Shocker - components blown in new machine

Q3: Are there other components that are likely to have blown too?

Most likely. That is why the fuse would blow. However, to say something that is useful means you must first provide some hard facts. Such as voltage numbers found on some label nearby the power cord attachement.

Pictures show what could be a supply that works from 85 to 265 volts. Then damage (due to UK voltage) should not happen. Pictures do not show enough numbers from enough parts. If that box is not for 230 volts (85 to 265), then a 400 volt capacitor or diodes (not shown) could be damage.

Most damage occurs without any visual indication. IOW it is blowing fuses due to those other damaged parts. Fuses typically blow after other parts have failed - to avert fire due to those other failed parts.

Also remove any failed varistors before trying another fuse. If a varistor is a reason for blowing more fuses. But first, what a power supply is actually designed for (what specifically are the voltage numbers) must be provided. Without even those numbers, all posts can only be speculation.

[Douglasbell01]

Re: High Voltage Shocker - components blown in new machine

Thank you all for such good feedback. It may be that there are other blown parts, but I will try to fix the varistor/fuse and re-test.

The machine is for the US market, so operates at 150v rating.

It's a 10mm Varistor. Just found one on eBay (150v) for £1.15, thanks to above comments.

http://www.ebay.co.uk/itm/VARISTOR-1...item3f273b7ee8

So... I could/should fit a higher voltage varistor (cutting out the need for a step down transformer)? This sounds risky - thinking that other components may not like 240v. Paranoia? Please do comment if you think that risk of damaging other parts is substantial, or not.

[cheapie]

Re: High Voltage Shocker - components blown in new machine

So... I could/should fit a higher voltage varistor (cutting out the need for a step down transformer)? This sounds risky - thinking that other components may not like 240v. Paranoia? Please do comment if you think that risk of damaging other parts is substantial, or not.

Don't do that. If the other parts could handle 240V, they would have put in a higher voltage varistor and sold it as a 120-240V model (they would sell more that way).

Just make sure you get at least a 150V varistor.

[westom]

Re: High Voltage Shocker - components blown in new machine

Thank you all for such good feedback. It may be that there are other blown parts, but I will try to fix the varistor/fuse and re-test.

If it is a varistor, then remove the defective part and power it up. The varistor, in normal operation, acts like it is not there.

Do this because the same part could also be an inrush current limiter. If the later, then it will not power up.

Before optaining the proper part, first determine what the input voltage should be on its label (often near the power cord). If it is an 85 to 265 volt power supply (as it may be from what little I can gather from the pictures), then a 150 volt varistor is too small.

[budm]

Re: High Voltage Shocker - components blown in new machine

As shown in your picture"10D271K" is 175VAC MOV 10mm Dia..
https://cdn.badcaps-static.com/pdfs/...699bb5481f.pdf
So the unit is not made to operate on 230/240VAC

[Douglasbell01]

Re: High Voltage Shocker - components blown in new machine

Hopefully these additional pictures will help. There's not much info with this machine regrettably, but there is a label on the bottom (picture #2).

I'm trying to find a 10mm MOV with those values on ebay.co.uk without success.

Following the advice in the previous post (thanks!)... the closest component I have found is a 7mm MOVs on eBay UK with those values (271K / 175 VAC): http://tinyurl.com/nc64or4 - would that replace the blown part, or is there something critical about the MOV's diameter?

Any help you can give in identifying the correct one (for sale) would be hugely appreciated.

[Douglasbell01]

Re: High Voltage Shocker - components blown in new machine

Found these on eBay (in China, but cheap Int'l shipping) http://tinyurl.com/kkvfpsp

[budm]

Re: High Voltage Shocker - components blown in new machine

So it is made for US 110~120VAC as I expected, the one on EBAY is fine, bigger diameter will handle more surge current as you can see in the spec sheet.

[cheapie]

Re: High Voltage Shocker - components blown in new machine

I would still recommend trying it without the MOV (but WITH the voltage converter) just to make sure nothing else is blown.

[budm]

Re: High Voltage Shocker - components blown in new machine

I agree, the unit will run if nothing else is damaged, it does not need MOV to run, MOV is just for protection. I would take the resistance reading on the two legs of that large 400VDC black cap, and also check the Diode, MOSFET, etc for low resistance readings.

[Douglasbell01]

Re: High Voltage Shocker - components blown in new machine

Just to double-check, is this an appropriate voltage convertor for the machine, or is the Amp output too low? http://tinyurl.com/o5wguur

The convertor that I've bought has a 45VA Output (just checked). While the unit's label states 0.9A Input... so it seems likely that I actually need a converter with 100VA output.

(Workings: 0.9A v 110v = 99VA)

To expand on testing methodology: I've recently removed the broken MOV.

Before removing the broken MOV, I tested a new fuse (pinched between the wires with 'blu tak' to help grip - the holding caps had to be removed to get blown fuse out), with the Voltage Convertor in use. 2x fuses blew instantly, but the machine's lights powered up for a second.

I've since ordered a new fuse holder (one that will allow fuses to be changed easily). I've 8 spare fuses. Still to purchase a new MOV.

What is the smartest next step in this scenario? I've not got any kit for testing resistance.

[budm]

Re: High Voltage Shocker - components blown in new machine

The power source should be rated at 20% higher than the requirement to have head room. If the fuse is still blowing, then you still have shorted components on the board that need to be checked. Good clear pictures of the whole board, both sides of the board?

[goontron]

Re: High Voltage Shocker - components blown in new machine

budm .9A machine but the converter can only supply .5A
ITS OVERLOAD NOT SHORT

[budm]

Re: High Voltage Shocker - components blown in new machine

Fuse of the power supply or fuse of the step down transformer?

[goontron]

Re: High Voltage Shocker - components blown in new machine

when the fuse blew, did it blow scattering metal in the fuse or did it blow without scattering any metal?
this is an old trick that is used when repairing valve sets if it blows clear its overloaded if it scatters metal its a short.(yes i am talking about the fuse, not the valves)