Saturday, 12 March 2011

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$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 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.

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