Today, while running sound at church, we had a singer in who required accompaniment tracks from two separate CDs. No big deal. Except that after the service had started, the VFD Display on our Sony CDP-CE535 CD changer pretty much failed entirely.
For some time, the display had been fading in and out. Each of us on the sound team knew that if you tapped the plastic in front of it, it would usually glow back to life. That was how things were going during sound check. Once the service began though, I couldn't get it to react at all.
I knew I couldn't spend the whole service banging on the front of the CD player, so I found a "Timmyrigged" fix with a screwdriver. Prying the underside of the VFD unit up from outside the unit would make it glow on so I could swap discs/tracks during the special music.
(It apparently thinks I love it. It was mocking me.)
I was interested in saving the church some money, so I took it home and decided I'd give repairing it a try. I suspected it was a cold solder joint causing the issue, as the whole display would fade out. While I've worked on plenty of electronics, I thought it would not likely be repairable. Turns out, it was easy to repair.
I do not know if this was an isolated incident, or if many of these units will exhibit these symptoms. The issue with this one was indeed a solder joint that was either a cold joint or possibly even corroded, it was hard to tell. If your display fades out entirely, and sometimes comes back on, read on for some help on repair!
About the Unit
This is a rather high-end 5-disc component changer, with some editing controls and the ability to feed in a 2nd audio feed for mixing. It was manufactured in September, 1999, and has seen duty once or twice a week since it was purchased new by our church.
We start out by removing the four black screws from the sides of the unit, and two from the top rear. Once these are removed, you can pull the top out from the sides and lift it off. It may stick just behind the plastic front panel, it is not attached; pull firmly and carefully and it will come loose.
Then, remove the screws on the bottom indicated by the red arrows here:
On the top, remove the two screws from the front panel support bracket as seen here:
At this point, I gently pulled the front plastic panel forward. It was then that I discovered a ribbon cable that couldn't be seen on the bottom half. My pulling it out had caused it to pull loose, which needed to be done anyway. So, to remove the front panel, gently roll the whole front panel upward, toward you, and then lie it on top of the changer tray face down. Be careful of the right-side ribbon cable!
Now, pull the right-side ribbon cable out of the connector on the lower right side. There are no buttons or clips that hold this in, it is held in by pressure in the connector. Grab it as close to the connector as you can and pull it in the direction as seen below, indicated by the arrow:
Now, you should be able to move the main body of the CD Changer aside and concentrate on the front panel itself. Gently lie it face down and remove the top support by removing the four screws that attach it to the panel:
Lay the support bracket aside.
Now, we need to remove the track control knob. Grip the panel firmly and pull on the knob firmly until it comes off. It will be a bit tough, but it is not held in with a screw or anything and will come off with enough pressure.
Lay the panel face down again.
The circut boards in the front panel are sectional; there are two halves, though as you can see aren't split 50/50. We are removing the larger of the two, the portion that the larger ribbon cable is attached to. Remove the screws as indicated by the red arrows:
Once the screws are removed, gently remove the circut board from the front panel.
Be careful with the front panel buttons, you might want to pull them out gently. They are only held in by the board we just removed. We will need to rotate the panel in a moment, so pull them out and make sure you know where they go back in!
Now, we can look over the display board:
The display itself is a VFD (Vacuum fluorescent display) unit (thanks to youtube user "vhsmemory" for this info!). This is similar to the more common (nowadays) LCD unit and LCD screens, except it uses more power and tends to fade over time. These units are pretty much a 1970s/80s technology, but they are still commonly found in Alarm clocks, microwaves, and plenty of DVD players and such.
Like I said above, the fact the whole unit goes out vs. a few parts of it, etc, and the cd player keeps playing and the buttons on the console still work, made me think there must be a power supply issue to the VFD unit itself. After flipping the unit over, I quickly found a suspect spot, where two standalone pins that go to the VFD were. Near one a "+" was etched in the silicone, so I'm 90% sure this is one power feed to the whole unit.
I then decided to plug the ribbon cable back into the main board and do some bench testing. It took only a moment to discover that I'd have to hook the other half of the front panel to the main board under the cd player in order to power up, as the power button was on that half of the controls.
To hook the smaller ribbon back up, you must remove the bottom of the main unit. If you take all the screws out of the bottom, the metal plate will come loose separate of the rear metal plate, which is nice because you don't have to remove the power cord or the rear inputs and such.
At this point, you can reattach the ribbon cable. Caution must be exercised with this same board under the changer tray, as it is what the AC transformer is attached to, so high voltage is present when the unit is plugged in, and possibly stored in the capacitors when it is NOT plugged in. See below:
Once you get it assembled, it may look something like this:
Make extra sure of two things: that the board with the VFD unit on it is NOT touching the metal plate on the back of the unit, or it could short out and destroy the whole unit for good (the whole entire changer, that is.) Also, it is a good idea to make sure something is propping the unit up while it is on it's back, like the laundry basket in the photo above. Make sure it is not touching the changer table, as it will rotate when we power up for the bench testing while it checks for discs during start up.
Once you are sure all is ready, plug it in and power it on to see if you can discover the source of the trouble. Watch this video and see what I found. First, you see me putting pressure on the display like I did during the church service, and it indeed makes it come back on. Then, you see me putting pressure on the suspect solder joint, and with very little pressure and movement I can make the display react. Then, you see my applying new solder to the connections and another test where everything is working great, even with pressure on the display that should have made it stop working in the prior condition.
Good luck with yours! Here, for fun, is my reassembly, sped up 1000%. Good times!