embedded PC Broken USB ports

This was a batch of embedded PC's with broken USB ports. Rough treatment had seen the supports snap off making the whole thing very wobbly.

The only key here is heat, lots of it.

This isn't the most interesting fix but its worth dwelling on some of the fundamentals of this kind of repair.

1. Patience, never rush the de solder, pulling on the component while applying the heat could have disastrous effects, pulling out the through holes or lifting the track.

2.Choose the right weapon, see that big ground plane there ! and what about the multi layers, thats going to take a lot of heat, if your iron cant cope it will never realy get hot enough and ..... see point 1 ! Experience has taught me you should only attempt the de solder if you have the right iron to hand.

I solder sucked the middle four pins and used a HUGE iron to get the four outer pins molten and pulled it, solder braid or solder sucking would just not get the holes clear so pulling was the only option, now I have just warned against pulling but you just have to get a feel for it and hold back until its hot enough.

On this board you can see the four mounting posts have all snapped off, this actually made the de solder easier as that metal shell would have pulled a lot of heat away. In fact I had another (I should have taken more pics) where the shell was fine (contacts inside had been mangled) but I purposely broke the four tags before attempting the de solder.

For this one I hadn't got the spare connectors yet (the connector was fine, just the mounting tabs were faulty) so improvised by making straps out of tinned copper wire and re used it.

A nice fix but for the others I used brand new connectors, only about £1 each.

The PC's were AMD Geode based which I had not come across before. They are AMD's competitor to Intel Atom.

Asus Eee PC noisy fan.

Not a lot to this one as I unfortunately didnt take any pictures of the interesting bit.

An Asus Eee PC 1000HD had an intermittently noisy fan. The case came apart fairly easily, starting with keyboard removal, there are sprung loaded tabs along the top row of keys and some tabs that you push on the underside.

You then need to remove all underside screws to release the heatsink plate / top shell.

Here is a pic of it at that stage, you can see the fan on the left, it is between the bottom shell and the mainboard.

Finally remove the screws in the screen hinges / remove all cables to allow the mainboard to be moved clear of the bottom shell, the fan can them be removed.

On the bench the fan was running fine but the fault was intermittent.

Here is a library picture of the fan

The metal plate was removed by taking out the three screws, what was evident was that the fan blades had been rubbing on the metal plate and scored a groove in it, its possible this was creating the noise.

The blades lift off , the shaft is located in a brass bushing, wear of this part may have caused the rubbing. The bushing was lubricated and the plate re fitted with washers spacing it slightly away from the blades to prevent rubbing.

We will see if this gives it a new lease of life, I will report back how it runs in the long term. A new fan is not so much £10, if I had known before I was asked to look I think I would have just told them to get one to replace.

Stanton C.314 faulty LCD display.

The fault with this Stanton CD Deck was that not all of the display was working. The unit itself functioned ok but just having part of the display working was very distracting as you couldnt see where in the track you were etc. in the pic the sub digit of the pitch setting in the top left is totally missing.

A search on the web showed a lot of people complaining about reliability of these units. This in turn seems to hurt used values.

Having had one in bits Im undecided, they are not bomb proof for sure but they arent priced at the top end of the market either, however Im sure a DJ deck will see a pretty hard life regardless.

There was a lot of talk on the web about an under specified capacitor on the power supply causing trouble, rebooting, not powering on etc, both the units I have seen had factory fitted (you could tell buy the bonding to the board) uprated 10,000uf caps (earlier units got a 6,800uf). These with the 10,000uf were dated July 2007 and Sep 2007.

So just a few segments not working, I checked for bad soldered joints and everything seemed ok. Also after some time and under close scrutiny the segments that were not lit did actually look like they were trying to be driven, at the right angle you could see that some were being driven / changing state, just very faint, some were totally absent though.

I took the LCD substrate off the PCB with a view to driving individual segments, what I found was that with just the charge on your fingers (or with a meter on diode check) by touching the pins in certain ways you could make segments switch state, including the ones that wouldn't work when connected !! ??

This made me think the driver chip was at fault.

I looked at the data sheet for the LCD driver a sitronix st7066u

http://www.sitronix.com.tw/sitronix/product.nsf/Doc/ST7066U

http://www.sitronix.com.tw/sitronix/SASpecDoc.nsf/FileDownload/ST7066U614654/$FILE/ST7066Uv22.pdf


and started poking arround with a scope to try and determine if an output was at fault, they all seemed to be the same though. My main focus was arround the pitch digits on the display that were not lit as moving the pich slider should have had this digit (seven segments) changing , I found the exact pins responsible for driving these segments (by looking on the scope while moving the slider) and they seemed to change state correctly. I then wired the driver chip outputs for these pins to other different pins of the display. Sure enough moving the pitch slider made the other segments change state, so it must be the LCD itself.

It was interesting to read up on how the LCD worked, duty cycle and voltage levels that multiplex the segments (the data sheet explains more), it wasnt something I had not dealt with down to this level.

Whilst I was probing arround the LCD driver chip I found that if you grounded an output, the chip went into a fault state where it would illuminate every segment of the display and in this state the faulty segments still did not change state.

Sooo.... I needed a new display

Stanton UK service centre wanted £200+vat for a full top board. Oh dear.

A second call asking if they could 'find' me a scrap one led to an offer of a scrap top board for £50 delivered, a generous offer to be fair but not realy the ballpark I was working in based on the used value of the unit.

A lot of calling round independant DJ service people was a mixture of no chance or hopes being raised then dashed, only one guy was rude to me, mostly very helpful.

Finaly Steve at www.trusound.co.uk he sold me a scrap unit including LCD for £30 delivered, great guy to deal with and he saved the day.

Here is the donar, all segments working, interesting to see the amber display on the lower specified unit :-)
(error is due to the fact this unit had no CD drive fitted).

So LCD swapped over it was time to see !....

Nice, all working.