CED VideoDisc and Player Discussion

[bertssat]

I bought my first 400 on ebay. Came with a remote but discription said front buttons didnt work, After arriving confirmed front panel not working so after reattaching the connector which had came loose, alas still didnt work. after close examination the connector pins where they are crimped to the strap was in very, poor condition, I had a front cover of the lowly sjt90 which lacks all the good buttons, After removing the button array It has the same circuit board that my 400 needed, To make a long story short, I used the front panel of the SJT90, but with the button assembly from the SJT400, and reattached correctly. I now have a fully funtioning SJT 400, now I could have taken off the buttons and put on the 400 front but may had risked damaging the buttons in the process, This info is just being passed on so othere can do simular repairs, My next tinkering is to make a SJT front to have all the functions as a higher machine,(I have anouther 90 with a front from a 200 so I know it works) the buttons are there hidden behind the front and the circuitry is also there. What RCA was thinking I have no idea, the buttons to go backward to see a missed or see again would have added only pennies at the time., You can e-mail me at bertssat@aol.com
Thanks
Bert

[toasterking]

I realize that this thread is a few years old, but this seems an appropriate place for this post. Having just successfully repaired the membrane keypad behind the front panel buttons in my SKT400 with a Caig Laboratories CircuitWriter Pen, I feel I should at least share my experience with the group.

I bought an RCA SKT400 player with a few problems on eBay. One of the problems was that most of the front-panel buttons did not work -- ever since I've had it I've used the remote for the reject, play, and pause functions (most of the search buttons did not work either), and tonight I finally decided to try repairing it again.

I believe all of RCA's J/K series players use the same type of membrane keypad behind the front panel buttons, so these notes should apply to all J/K series players.

Behind the plastic buttons is a membrane keypad. To access it I removed the front casing (instructions are printed and glued to the underside of the top cover), then removed 3 "nuts" attached to plastic studs to remove the button assembly.

The membrane keypad consists of 4 plastic film sheets glued together:
# | Description
1 | Protective cover (outermost layer)
2 | Conductive "button" contacts
3 | Spacer to separate layers 2 and 3 to prevent keys from being accidentally activated
4 | Conductive traces

I peeled layers 1, 2, and 3 completely off, one at a time. After measuring resistance on the traces of layer 4 with a digital multimeter, I found that multiple traces had fractures in 2 main places:
- Where the film "cable" bends
- Where the leads are crimped onto the film cable

I needed a way to repair those traces to make them conductive again which would not damage the plastic material and which would retain flexibility. For this the Caig Laboratories CircuitWriter Pen was perfect. I got it at RadioShack, cat. no. 640-4339. It was on clearance and I was told by the salesperson that they plan to no longer stock it in stores, but looking on their web site, it still appears to be available in stores months after I bought it.

I cleaned layer 4 completely with isopropyl alcohol and a white t-shirt, removing all of the sticky residue from the glue but being careful not to rub so hard as to thin out the conductive material. I used the pen to "draw" new traces over the existing broken ones, and the pen's conductive polymer did quickly bond to the plastic film and complete the circuit, just as advertised. If you're new to this, practice on a similar surface first, such as the plastic blister pack the pen is packaged in. It is very easy to dispense too much material and make a mess of your circuit. I "drew" over all traces where the cable bends. For the crimped leads, I drew new traces on top of the black insulative material between the crimped leads and the film traces, bypassing the poor connections where the leads are crimped.

After waiting 5 minutes for the new traces to dry, I then checked resistance on them again with the multimeter. Then I overlaid layer 3 on top of layer 4 where it used to be, being careful to line up the film with the keyed studs on either side.

I found that because of the way I stressed the plastic when I peeled off layer 2, the contacts now got "stuck" in the inverted "down" (concave) position when pressed and no longer sprung back out. To remedy this, I folded layer 2 laterally, ensuring that all contacts were in the center of the fold. This trained the contacts to spring outward again, though they now spring a little more strongly than they did originally.

Since the film membrane layers would no longer stick together, after lining up all the layers layers I secured them to the plastic casing with ordinary Scotch adhesive tape at every edge. At the end of the flexible film cable, I wrapped a piece of tape all the way around all 4 layers to hold them together.

After reassembling the front panel and reattaching the front casing to the player, all my front panel buttons are working for the first time. Yay!!! I believe the buttons travel a little further before making a connection than they did originally (because of my folding trick), but at least it is working reliably. The best aspect of this repair is that it did not require obtaining any new parts or sacrificing them from another player.

I'd like to know if anyone else here has attempted a repair of the membrane keypad, what methods you used, and what your results were. If you have any suggestions on how I could improve my method, please share them with the group.

[CEDatum]

A front panel membrane switch assembly is used in all RCA J and K line CED players. The Japanese made CED players use reliable miniature tactile switches for front panel function selection. RCA had problems early on with the membrane. In an internal Service Information Bulletin
( File 1983 -Service Info No 3 ) RCA advises that the membrane assembly is available as a separate item,stock no 157861.
Problems with the membrane are - the dimples under the front panel switch selectors get pushed in permanently. The membrane lines at the connector can fracture.
CEDatum offers a repair kit that will permanently fix front panel problems. The membrane is REMOVED COMPLETELY and miniature tactile switches are installed. The kit comes with full installation instructions. Some soldering is needed. Or you can just send your complete front panel to us an we will install the kit at a reasonable price.

Contact CEDatum for details. cedatum@ccrtc.com

[toasterking]

Hi John, good to hear from you! I recall a discussion we had a couple of years ago about the possibility of a kit like this, but you indicated there did not seem to be much demand for it, so I didn't really expect to see you invest all the research and experimentation to create one. I'm glad you proved me wrong! Hopefully this will serve as advertisement and more owners will recognize this as a worthwhile upgrade.

I personally am disappointed with RCA's design choices in their implementation -- especially the film cable interconnect which appears to have been fitted as an afterthought. I had the problem with the dimples too, as I noted, but was able to resolve it by reshaping the membrane itself. Although a kluge, it works well, but I expect that with extended use will come excessive wear since the membrane will be flexing more than usual. This was my first repair using a conductive polymer pen and I was impressed with its performance, though I can't say yet whether I would trust it to an "important" project. The only advantage of my method is that it doesn't require parts -- your method is definitely superior and is the approach RCA should have taken in the beginning, although the percentage of membranes that performed acceptably probably justified the cost savings for them at the time.