Interesting Repair Of the Day – Raymarine E120 classic back light repair.

I’m starting to see quite a few E120 classic MFD’s come my way with dark displays – usually because the back light high voltage power supply circuit crapped out.

The back light in this unit consists of a number of high intensity, miniature florescent bulbs – commonly known as CCFL’s – or Cold Cathode Florescent Lamps. They require a pretty high voltage in order to illuminate – something in the neighborhood of 1500 to 3000 volts. On the other hand, the current requirement is quite  minimal, perhaps a few milliamps.

To create the required power, Raymarine has employed a classic “switch mode power supply” circuit that uses a pair of FETS to drive battery voltage through a pair of step up transformers. It’s quite effective, but my guess is the circuit is running at the top end of it’s design parameters when it feeds power to the long and numerous CCFL tubes in the E120. The same board is used on the smaller E80,  and I have yet to see this kind of failure in that model. .

The repair process is quite technical and well beyond the scope of most repair shops. The real challenge is the removal of the failed components without causing additional damage. Under the best of circumstances this is often unavoidable, and the repair tech better bring his “A game” to the effort!

The circuit board containing the high voltage power supply is a “multilayer” type – having not only a top side and a bottom, but several layers of copper and fiberglass – in between. It’s all tightly pressed together into a solid “board”.

Unless you have access to a first rate vacuum desoldering system and a hot air re-flow machine (for dealing with the surface mount components) – AND possess the skills to properly use them,  you run the very real risk of trashing the board while attempting to repair it.

BTW  – replacement boards are no longer available!

 

The E120 shown below has suffered a Fukashima grade melt down! One of the FET’s burned up so thoroughly, it fried the copper in the circuit board it was soldered to.

Click on the photo’s  for a better view.

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Note the fried FET on the left.

 

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A better view with the transformers removed.

 

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This photo shows the the board with the FETs removed, and clearly illustrates the full extent of the damage. The copper below the FET on the right has burned away, and the pad where the FET’s Gate lead is normally connected, fell off once the FET was removed.  This circuit got HOT!

 

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To repair the damaged board, I carefully fabricated  a patch out of thick copper foil that matched the shape of the original copper on the circuit board. It was cleaned and prepped on both sides with a thin coating of 63/37 solder. The patch was carefully aligned, then soldered in place.

The photo does not show it well but there is a very small wire where the FETs gate connection pad once was. The copper trace that brings the gate drive signal to this FET  is on the other side of the board. It is connected to the pad by way of a  VERY small “micro-via” – essentially a small metallic tube filled with solder – that penetrates the board and connects the pad on one side, to the trace on the other side. Once the pad fell off, there was nothing of substance to solder the FETs gate lead to.

I managed to melt the solder within the micro-via  and simultaneously insert the hair sized wire THROUGH the micro-via where it will ultimately be soldered to the FET’s gate, thus restoring the connection.

Tricky, precise business…

 

 

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Not real pretty, but damn sure functional!  It cleaned up nicely.

New FET’s and transformers were installed, and the unit was reassembled and powered up.

 

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SUCCESS!!!

A repair is worthless unless it’s reliable, so I let every unit run overnight and well into the next day.  This photo shows the unit in operation after an  18 hours bench test. It’s going home to a happy customer who just save a WHOLE bunch of money!

 

Comments

  1. Louis Graham on September 18, 2013 at 2:15 pm

    Hi Steve,

    Thanks for the in depth description. Good to know there are still companies (and people) with integrity and great skills.

    Regards from Marine Automation, Inc

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