Putting this up for posterity. I have an Astrotech LC2P which wasn't working. The display would be a bit random and frozen, but the unit seemed to work if I just pressed gently on the front of the case. Seems like an obvious intermittent connection. I'm also aware that the buttons on this unit are notorious for stopping working, and respond well to some contact cleaning. I later found one of my buttons didn't make good connection, so I did that.
The unit has 3 wires in the back. Black is ground, red is 12V, and white is 12V for the backlight.
Opening the unit, there is very little to it. The IC is an epoxy button to the board. There is an oscillator crystal, and 3 film capacitors. The caps are rated!! This cap style is not likely to ever fail. There is a small ceramic adjustable cap likely for fine tuning the oscillator. There is an LCD 40 pin DIP, which is likely a Standish LCD Model 3906. I found a PDF with the pinout and theory of operation. It's worth mentioning that no DC power goes to the LCD. Read the PDF if your not familiar with how these work! The buttons are interesting construction. There is a metal foil punched part with two pins and if you desolder it, there is a small contactor underneath soldered to the board.
To clean the buttons you need to desolder the top metal part and remove it. Don't desolder the middle pin, you can leave it on the circuit board. I used deoxit and a Qtip to clean the parts and that worked great. Isopropyl alcohol would also work. I checked the resistance before and after cleaning and worked much better afterward.
The bulbs are small 12V bulbs. Not sure the model #, but I've seen plenty similar replacements for vintage radios and electronics gear. Should be easy to replace or even mod with LEDs.
Looking at the board, there was some mediocre solder joints, poorly made jumper wires, and some cold solder joints with the pins having a pit of corrosion. One of these was intermittent and causing my problem. I applied a small amount of rosin flux and reflowed the solder joints making sure to get flux on the corroded pins and they cleaned up.
The 40 pin DIP LCD has a common pin at pin 1 and 40, top and bottom left when looking at the display side of the unit. Pins 1-3 and pins 38-40 look all bridged together. The other two pins in those are no connection, and the common was a cold joint, so the cold joint would not connect and the display would drop out, causing my problem. It was clear that it was a display module issue because the unit would still keep time despite losing display. If the clock IC was losing power, it would reset the clock. I knew to check the common leads on the LCD because the whole thing would drop out, all other pins are wired to each individual display segment, so if you have a dead display segment you can use the schematic to figure which pin needs attention.
Of note, this unit is incredibly easy to service, and I was able to find replacement LCD units on ebay, so the only way this unit would be unrepairable is if the IC itself was dead.
Of course, if you need to repair your unit, I beleive you will need an FAA authorized repair shop to sign off or conduct the repair. If you aren't a skilled solder jockey, find a repair station who is willing to reflow the solder joints for you and clean the contacts, and this unit will likely last a lifetime.
A few other notes - It looks like the form factor for the LC-2 and LC-6 is the same, so if you have an unobtanium yoke mount part, the panel mount parts are likely identical inside
The unit has 3 wires in the back. Black is ground, red is 12V, and white is 12V for the backlight.
Opening the unit, there is very little to it. The IC is an epoxy button to the board. There is an oscillator crystal, and 3 film capacitors. The caps are rated!! This cap style is not likely to ever fail. There is a small ceramic adjustable cap likely for fine tuning the oscillator. There is an LCD 40 pin DIP, which is likely a Standish LCD Model 3906. I found a PDF with the pinout and theory of operation. It's worth mentioning that no DC power goes to the LCD. Read the PDF if your not familiar with how these work! The buttons are interesting construction. There is a metal foil punched part with two pins and if you desolder it, there is a small contactor underneath soldered to the board.
To clean the buttons you need to desolder the top metal part and remove it. Don't desolder the middle pin, you can leave it on the circuit board. I used deoxit and a Qtip to clean the parts and that worked great. Isopropyl alcohol would also work. I checked the resistance before and after cleaning and worked much better afterward.
The bulbs are small 12V bulbs. Not sure the model #, but I've seen plenty similar replacements for vintage radios and electronics gear. Should be easy to replace or even mod with LEDs.
Looking at the board, there was some mediocre solder joints, poorly made jumper wires, and some cold solder joints with the pins having a pit of corrosion. One of these was intermittent and causing my problem. I applied a small amount of rosin flux and reflowed the solder joints making sure to get flux on the corroded pins and they cleaned up.
The 40 pin DIP LCD has a common pin at pin 1 and 40, top and bottom left when looking at the display side of the unit. Pins 1-3 and pins 38-40 look all bridged together. The other two pins in those are no connection, and the common was a cold joint, so the cold joint would not connect and the display would drop out, causing my problem. It was clear that it was a display module issue because the unit would still keep time despite losing display. If the clock IC was losing power, it would reset the clock. I knew to check the common leads on the LCD because the whole thing would drop out, all other pins are wired to each individual display segment, so if you have a dead display segment you can use the schematic to figure which pin needs attention.
Of note, this unit is incredibly easy to service, and I was able to find replacement LCD units on ebay, so the only way this unit would be unrepairable is if the IC itself was dead.
Of course, if you need to repair your unit, I beleive you will need an FAA authorized repair shop to sign off or conduct the repair. If you aren't a skilled solder jockey, find a repair station who is willing to reflow the solder joints for you and clean the contacts, and this unit will likely last a lifetime.
A few other notes - It looks like the form factor for the LC-2 and LC-6 is the same, so if you have an unobtanium yoke mount part, the panel mount parts are likely identical inside