Yaesu FT-857

Display issue

I recently acquired a Yaesu FT-857 with the 'zebra stripes' issue on the display.

FT-857 showing a moderate case of the stripes...

Lore in the hamdom suggests this is a problem with the adhesive on various parts of the flex cable that attaches the LCD display to the main head unit pc board. This problem is not unique to this Yaesu -- many other radios, clocks, etc. will exhibit this problem at times. Unfortunately it seems the adhesive used on these displays tends to age and reduce quality of connectivity between the controller and the actual display.

A closer look

The "display" on the FT857 looks to actually be three separate parts:

  • flex cable soldered to main PCB: This flex cable is soldered to the large green PC board that makes up the majority of the head unit. It also looks to have a controller for the LCD encapsulated directly into the middle of this flex cable. It is soldered to the main display and also looks to have some sort of adhesive holding it mostly tight to the main PCB. I think this would separate with minimal effort but will likely destroy the fragile solder connections to the main PCB -- not my goal right now.
  • intermediate flex cable: This flex cable is between the afore-mentioned flex with the LCD circuitry and the display itself.
  • display: It's glass -- probably fragile. I'm not going to find out.

The display or entire head unit are maybe available from Yaesu parts. I've purchased other parts from the Yaesu parts folks before -- real parts, great prices. As of now I have not inquired about pricing or availability for a new display.

Can I fix it myself?

As you can see in the previous picture, it's going to be difficult -- but not impossible to use the radio as-is. If I can get the display to work better without replacement that'd be great. I hope not to break it in the process...but if I do...I'm looking at replacement anyway.

What the problem is *not*: it's not the solder connection to the main PCB and it's not the connection from the CPU to the main board. I re-flowed all of the connections in question there with no difference.

I found that the interface between the flex cable soldered to the main PCB and the intermediate flex cable to be the problem for my unit. After disassembling the control head I used a heat gun to warm up the rounded end of a dental tool. Note I'm heating the tool, not the flex cable! How hot? Not hot enough to burn the back of my hand but stings a bit -- maybe in the 150F range? With the heated tool I used some moderate pressure on the interface between the two cables and tried to re-mate them.

FT-857 better -- not perfect, but good enough for now

As you can see it's better but not perfect. Notable are the clarity of the menu and status lines. There are now only two major lines missing in the display which do not significantly impact the legibility of the information displayed. I will probably spend some more time re-heating the flex cable or tracing those lines under magnification to see where they lead.

But for now, I think this is adequate for a fix costing only an hour of my time.

This page last modified Thu Jul 7 10:27:27 CDT 2016 by timc!

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