GHD 4.0B's

This model is a MK4 pair of GHD straighteners in Black. Temperature regulation is performed by a thermistor.

Normal operation is as follows:

Switch on => Beep Once, LED on constantly
Reach operating temperature => Beep twice, LED flashes.

If the temperature of the irons is below 5 degrees C then they will not work and the will emit a continuous beeping sound. To fix this, just bring them back up to normal temperature (gradually!) and then try again.

The mains cable used on this model is the same as used on the Mk3 GHDs. This cable is available in the Spares shop.

The metal heater plates are the same used on the GHD 3.1B model. These are also available in the Spares shop.

The heater elements are 70Ohms each. When connected to the PCB they are in parallel, so you will measure 35 Ohms (if they are both working). Replacement heaters are also available from the shop.

Most common fault with this model is R8 going open circuit in the electronics causing them to be completely dead (see the R8 Failure page).

Circuit Diagram

Mike Broom has kindly traced out and sent me the circuit diagram for the PCB found in GHD 4.0B's. It can be downloaded here - GHD 4.0B Circuit Diagram. There might be some "funnies" with this diagram, however it's reasonably close. If you've got any corrections, please don't hesitate to let me know.

Electronics

I had one pair of these GHD's which seemed to be completely dead. I narrowed it down to the fact that the power supply for the PIC processor was producing less than 2.5V. After more investigation I discovered that R8 was open circuit. On replacing this they came back to life :-)

Here is a photo of a PCB where R8 has been replaced with a MELF resistor (which is less likely to fail compared to a "normal" surface mount resistor):

I can supply you with a suitable replacement resistors for £4 (inc P&P) - buy online in the spares shop.

In the process of that investigation I made a note of the following in case it's of use to you:

Component Reference Designator	Component Type / Value	Comments
R1	1 Meg Ohm Resistor
R5	1 Meg Ohm Resistor
R8	100 Ohm Resistor
R10	1 Meg Ohm Resistor
D1	Diode	During correct operation it should have about 2.2V across
D9	Zener Diode	During correct operation it should have about 2.15V across
C5	200uF 6V Capacitor
C1	0.22uF 275AC Tenta Capacitor
U3	ST Triac
U4	Microchip 12F675	Should be 4.5V between pins 1 & 8

The power supply circuit is based upon this microchip application note. In more than 1 pair I've seen, R8 had failed causing the straighteners to be completely dead (as the PIC had no power).