PSP Wifi Reflow

I recently bought an Aoyue hot air reflow station so I could do SMT soldering faster and more easily. £90 on ebay - bargain! As I repeatedly say, there's nothing magic about surface mount stuff - it can be soldered easily by hand with an ordinary iron and a little practise. However, hot air reflow does allow one to solder BGAs.

A friend came to me with a PSP wifi module with an insane problem - all the joints on the BGA had failed, and the module just sheared off, leaving perfectly tinned pads on the module, and perfect flat-topped balls on the PCB! Presumably it wasn't quite soldered correctly at the factory.

I added flux with a flux pen, and reflowed the balls so they were all nice and shiny and rounded again.

Then I preheated the pcb from the back and front, to prepare for soldering the BGA. I removed the sticker from the top of the module so it didn't burn. Flux was applied to the back of the module. I aligned the module roughly (the balls of solder do the rest) using a vacuum pick-up tool - a little freebie that came with the reflow station. I tried to be fairly quick so the board didn't cool down too much.

Then I heated the module mostly from the top. I heated it fairly gently over about a minute, heating a little more strongly towards the end. I poked the module with a screwdriver to feel whether the balls had melted. They had - the module wobbled on the surface tension like jelly. I didn't take any photos, as I was too busy worrying about whether I was overheating it!

I let it cool, then washed it in the ultrasonic bath with methylated spirits to remove the flux.

Nick reported that the module worked fine. I had slightly overheated a connector on the back, so it was a tight fit, but the board worked ok. 

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monitor repairs

Submitted by Andre (not verified) on Thu, 01/01/2009 - 14:12.

Hi there.. This is a very interesting repair trick, as I have a few Philips and other monitor PCB's here which don't turn on/stay on then shut down.

I did find that in a lot of cases the 2SC5706/5707 transistors go bad due to old age, replacing these does sometimes work as long as the secondaries are OK.

The best way to test them is to measure their gain on a Peak Atlas, if they measure the same they are probably OK. If one is really low then it is unbalancing the bridge and can cause a shutdown.

Another fault I ran into is shorted/open HV secondaries. This can be checked by measuring with a DMM, if they measure significantly different or one is much lower than the rest then it is bad. Usually you can tell by looking at the underside for charring and/or melted labels. Replacements can be fabricated if you have a donor PCB with a similar transformer, just wind the correct number and gauge of turns then test, possibly replace in pairs just to be safe?

As a last resort these *can* be run with only two of four tubes on a single transformer pair. It is possible to reroute the wiring so one of each pair is used to avoid a dark area. This also requires modifying the circuitry slightly but if the monitor is destined for the bin anyway then it is preferable.

Regards, -A