Thermal Fuse gone after R8 Replacement

dannytip
Posts: 2
Joined: 29 Apr 2012, 17:09

Thermal Fuse gone after R8 Replacement

Postby dannytip » 29 Apr 2012, 17:13

Ive been repairing a pair of 4.0b's for my girlfriend. Initially the R8 resistor was dead so i replaced that and they worked fine for 2-3 heat cycles.

After that the thermal fuse has now blown. Ive tested both heater elements and they come in at about 73ohms i also checked the thermistor and it seems to be still nicely attached to the heater plate.

Any ideas? Shall i just replace the thermal fuse and hope it doesn't blow again? Or could it be something else.

prettypriddy
Posts: 28
Joined: 01 Oct 2010, 13:24

Re: Thermal Fuse gone after R8 Replacement

Postby prettypriddy » 01 May 2012, 11:28

Hi,
I`d go for the cable my friend, as its that whick caused the R8 to blow
You don`t mention that you changed that so I`m guessing not.
As its a MK4.0 you`ll have the older style connection so a new cable should sort the problem. Oh and another R8

dannytip
Posts: 2
Joined: 29 Apr 2012, 17:09

Re: Thermal Fuse gone after R8 Replacement

Postby dannytip » 08 May 2012, 10:42

Thanks for your reply. Why does the cable cause the R8 to fail?

I tested the R8 and that is still good it's just the thermal fuse thats gone. There were no issues with the cable before the R8 failed.

gary
Site Admin
Posts: 1032
Joined: 26 Jan 2008, 00:44

Re: Thermal Fuse gone after R8 Replacement

Postby gary » 08 May 2012, 22:22

Hi Danny,

The R8 fails due to power surges caused by an intermittent connection. Therefore a dodgy cable normally kills the R8 resistor.

In your case however it sounds like a heater element has gone which has caused the thermal fuse to trip. I bet if you disconnect the heaters from the PCB and measure them again the non switch side one will be open circuit and the switch side one will be 73ohms. When both heaters are connected they should measure about 35 ohms.

If I'm right you'll need one of these:
http://www.ghd-repair.co.uk/shop/4.0B/7 ... thermistor
and a new thermal fuse.

Alternatively just send them away for repair as it's probably cheaper:
http://www.ghd-repair.co.uk/repair_service.html

Gary


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