Saturday, December 29, 2012

Signature Electronic Signs Inc repair

This post is continued here:

There are several Signature Electronic LED Signs for sale on EBay. I bought one that did not work and to get it working I had to add a power cord, and connect the 5 volt power to the processor board in the upper left corner.
Here is the right side of the back where the 110 Volt power is connected.

These signs are made with Cadaces CDVO-1 boards strung together.  Each of those boards holds 8 of 8 by 5 LED arrays.  TPIC68595 serial shift registers drive the columns and a 74HCT138 drives the rows via some TIP127's.  There are 12 of these Cadaces CDVO-1 boards in the sign.

The controller card has two wires that connect it to the outside world. One is green one is blue.  I have traced them out to a "485" IC.  That IC is a RS422 communications chip, so likely the sign is communicated with via RS422.  You will need a Serial or USB to RS422 adapter to talk to the sign.

Here is what one of the Cadaces CDVO-1 boards looks like.

Here is the back side of the Cadaces CDVO-1 board.  I have metered out the pinout and hope to post that soon.  Then I can work on interfacing it to an Arduino or something like that.
Here is how the Cadaces board connects to the controller.
 Here is a size comparison between the new sign and the old Silent radio sign
The new sign is now working with the Arduino processor, but there is a bug when trying to run the entire sign.  Each sequential board displays the same thing as the previous board, it is just scrolled down one position.
 I am using the same software as with the Silent Radio sign, but with the register clock jumpered to the serial data clock, and the column selection code has been modified to work with the 74138.

Sunday, December 16, 2012

Poloroid TDA-03211 3211 32 LCD TV Repair Part 2

I recently had to re-repair the Poloroid TDA-03211 3211 32 LCD TV. This time one of the tiny blue capacitors in the red circled area had shorted and turned black.

I could not read what was written on those caps so I removed them and tested them. The two good ones were about 1 pf, or at the range limit of my capacitor meter. They appeared to be 3 KV caps. So I replace the fried one with a 1 pf 3Kv capacitor and the TV still did not work.

The problem was that I had soldered one capacitor in wrong.  Two of them are part of the protection circuit that detects any problems and shuts down the High Voltage.  They have to be replaced properly or the set will shut off after about 5 seconds.

Here is a better picture of the power supply:
 I circled the blue caps, the tan one is my replacement capacitor.  Notice the large red caps, they are 2.2 uF at 400 volt paper caps that replaced the old 4 uF electrolytic caps.

Friday, December 14, 2012

Dunlap Clarke Rebuild part 2

A while back I started rebuilding a Dunlap Clarke Amplifier.  This is an update to the rebuild project.  I stripped the cabinet almost completely bare, then cut holes in the sided for new heat sinks.  Next I drilled holes for the power transformer.
Next I installed the heat sinks with the new circuit board and wired everything up. The new power transformer is 50 volt center tapped at 8 amps.
So far all I have done is a hum test.  I connected speakers and tapped the input screws to produce a loud hum.  Next is to wire up the input jacks and level controls.