Tektronix TDS 220 CRO

[Don]

Hi All,

Need some assistance in fixing a Tektronix TDS 220 Two Channel Digital
Real-Time Oscilloscope.
When the CRO is first turned on I have a faint display on the LCD
screen. This display disappears after about a minute or so. If I turn
the set off then immediately on there is the faint display again which
now lasts only for a few seconds.
It looks like temperature related or a bad solder joint (which I am
hoping it is). This brings me to the second problem - how do you get
it apart. I have separated the front keypad/control part but I am
having trouble with the rear case which seems to be held by the comms
port panel at the bottom behind the BNC sockets. It seems to me that
there maybe a screw or a catch that is holding the bottom PCB to the
rear case. Is it possible, and how can I remove that 100mm X 100mm
comms port panel or am I barking up the wrong tree?
I do not want to use any force for fear of snapping the printed
circuit board or worse still, cracking the LCD screen.
Any assistance will be greatly appreciated
Thanks in advance.

Don Goulding

 

[Don]

don.goulding@csiro.au (Don) wrote in message news:<fae88924.0405191918.11aaf525@posting.google.com>...

Hi All,

Need some assistance in fixing a Tektronix TDS 220 Two Channel Digital
Real-Time Oscilloscope.
When the CRO is first turned on I have a faint display on the LCD
screen. This display disappears after about a minute or so. If I turn
the set off then immediately on there is the faint display again which
now lasts only for a few seconds.
It looks like temperature related or a bad solder joint (which I am
hoping it is). This brings me to the second problem - how do you get
it apart. I have separated the front keypad/control part but I am
having trouble with the rear case which seems to be held by the comms
port panel at the bottom behind the BNC sockets. It seems to me that
there maybe a screw or a catch that is holding the bottom PCB to the
rear case. Is it possible, and how can I remove that 100mm X 100mm
comms port panel or am I barking up the wrong tree?
I do not want to use any force for fear of snapping the printed
circuit board or worse still, cracking the LCD screen.
Any assistance will be greatly appreciated
Thanks in advance.

Don Goulding

Hi All,
An update,

I have managed to separate the rear case by pressing in the spring tab
on top of the comms panel and gingerly levering it upwards. This
action unplugged the comms panel from the motherboard.
After checking the boards for bad solder joints and
removing/re-seating all plugs I now have a display which is still very
faint but on all the time.
On the power supply board there is a 4 way plug that has two leads
which goes to the top and bottom of the LCD panel. Un-plugging this
plug does nothing to the display. It looks like the supply for the
backlighting of the LCD.
Since this is the first time I am working on an LCD panel, what
voltage must I read across the pins (it seems that it must be very
high because of the silicone leads used) and should I get any
resisitive reading across the leads to the panel (reads O/C now).
BTW if I shine a lamp side on to the display the display is very
readable. It now looks like a backlighting problem to me.
Any ideas/thoughts/suggestions on this please.

TIA

Don Goulding