While there is a possibility that both the row and column drive transistor array failed, there is a high likelihood that the dot or diode where the faulty row and column intersect is shorted or faulty, causing the entire row and column to be shorted.

In that case, skip to ruling out electrical issues.

1. Manually flip dot to loosen dot
2. Check if dot is installed backwards (it will flip in opposite direction of other dots)
3. Check if dot came loose
4. Check if posts holding dot are bent or broken
5. Use compressed air to blow out debris behind dot
6. Remove dot and check for debris trapped behind dot

Disconnect dot board before electrical troubleshooting!

1. Check resistance of coil - expected reading is 18.5Ω (±0.5)
   1. Low resistance (close to 0 ohms) - coil is shorted and must be replaced
      (possible causes: scratched coil wire, melted enamel due to overheating)
   2. High resistance or open circuit - coil wire is broken and must be replaced
      (possible causes: physical wear and tear, corrosion)
2. Test BAV99 diode between pins of faulty dot: Pin 1→ Pin 3 and Pin 3 → Pin 2
   1. Conducts both ways - must be replaced, causes faulty row and column
      (possible causes: ESD damage or overcurrent)
   2. Open circuit both ways - must be replaced
      (possible causes: ESD damage or overcurrent)

If there is a row and column fault at the same time which intersect, it may be a faulty dot where they intersect, causing the row and column for that dot to fail. Try the above single dot fault resolution first in such a case.

Replace ICs according to this matrix:

* It seems like the sink drivers tend to fail first

• Hot air reflow gun - 330°C (higher temperatures may cause PCB surface to blister)
• Soldering iron - 280°C (63/37 Sn/Pb solder)
• Solder wick (pre-fluxed)
• Tweezers

• BAV99 diode

1. Heat diode up with hot air reflow gun
2. Gently nudge diode with tweezers to check if solder is molten
3. Wait 5-10 seconds for further solder reflow
4. Remove diode with tweezers
5. Use solder wick and soldering iron to remove solder from pad
   • Do not move the wick back and forth, it may rip PCB pads off
   • Keep solder wick on the pad(s) without moving and wait for solder to wick up

1. Apply small amount of solder to PCB pad for diode pin 2 (standalone pad)
2. Prepare diode in tweezers, and soldering iron in free hand
3. Re-heat PCB pad, place diode and align diode
4. Once satisfied with diode alignment, solder remaining pins - solder quickly, or wait between pins to solder, otherwise diode may heat up enough for pin 2 to melt and diode to move around

• Hot air reflow gun - 350°C
• Soldering iron - 280°C (63/37 Sn/Pb solder)
• Solder wick (pre-fluxed)
• Tweezers or needle nose pliers

• Faulty source (stuck yellow): TBD62083AFG,EL
  • (Faster and better replacement of ULN2803A and TD62083A)
• Faulty sink: TBD62783AFG,EL
  • (Faster and better replacement of TD62784A)

1. Heat faulty IC up with hot air reflow gun - heat the IC package instead of PCB to avoid overheating and blistering PCB
2. Gently poke solder at IC legs with tweezers to check if it is molten
3. Wait 5-10 seconds for further solder reflow
4. Remove IC with tweezers or needle nose pliers
   • ICs are glued down
   • Do not pull IC immediately, it may rip PCB traces below the IC off
   • Twist IC slightly back and forth until you feel the IC release, then pull upwards
5. Use solder wick and soldering iron to remove solder from pad
   • Do not move the wick back and forth, it may rip PCB pads off
   • Keep solder wick on the pad(s) without moving and wait for solder to wick up
6. Do not attempt to scrape old glue off, it may rip PCB traces below the IC off

1. Apply small amount of solder to PCB pad for pin 1
2. Place IC on pads, ensuring dot on IC lines up with pin 1
3. Press IC down with tweezers or needle nose pliers, then solder pin 1 down
   • You may need to bend all IC pins downward to make good contact with the pad, as the old glue lifts the IC slightly off the PCB
4. Repeat the diagonally opposite pin (e.g. pin 10 on transistor array ICs)
5. Solder pin 1 side, from the far end towards pin 1.
6. Solder the opposite side, from the far end towards the tacked down pin

Dots are really, really hard to replace. Some dots are single dots which are easy to replace, however the majority of dots are 7×1 modules where all 14 pins must be freed and replaced at once.

Standard desoldering technique for through-hole parts apply - use soldering wick or a desoldering gun.

However, the PCB holes are small and pins are fit very tightly, making it very difficult to fully suck/wick all solder out.

Tips:

• Be quick with the soldering iron or allow time for pins to cool, otherwise the plastic on the body of the dots will melt
• Applying force such as pulling on the dots while heating the pins will cause the dots to melt off the pins and ruin the dots, so don’t heat and pull at the same time
• Give up trying to desolder dots, instead use super glue and snap parts off dots from a spare board to try to repair dots rather than replace them