Dot Matrix

[VanillaSlicePie]

Dot matrix board from Rottendog was purchased approx 2-3 years ago, display about the same time on my CFTBL. After fixing a driver board issue and with machine turned on, plugged in the two connectors to the display and I now have a blank display. Yay....not!


So, keeping in mind you need -12v within +/-10% apart from pin 1 (-115v) and pin 2 (-103v) on connector J604 for the display to work, my readings are -131v pin 1 and -107 pin 2. According to the Rottendog schematics, -118v pin 1 and -105v pin 2.


My query is how to reduce the higher volts to within the -12v range? Have buzzed out tracks, checked fuses, connectors and reseated cables. All other voltages are correct. (+5 +12 +62)


Any helpful handy hints appreciated.

[Strangeways]

Measure the voltages with the (or another) DMD connected. Voltages change with a load.

[VanillaSlicePie]

Voltages are the same at DMD connector and don’t have the convenience of another DMD. However, not sure how I missed this but no +62v at DMD connector yet there is at the connector pins on circuit board with the connector unplugged.??

[VanillaSlicePie]

At this stage the 68v is dropping down to 6v when connected to the DMD Display. When the power connector is removed from the DMD display 68v returns to circuit board connector.


So, on the pins on the DMD display, pin 8 (68v) and pin 6 (5v), is reading continuity on my MM. 
Without the schematics, can someone clarify if this is correct with their WPC board or is this the frustrating short I’ve been looking for?

[Strangeways]

I've just checked Pin 6 (+5V) and Pin 8 (+62V) on a new Display and there is no continuity on my digital multimeter. There is no relationship between the pins on the schematic. There will more than likely be an issue with a transistor short within the VSP circuit (+62V).

[VanillaSlicePie]

Appreciate the help. However I’ve had to email the supplier of Vishay dot matrix display for schematics and to the best of my knowledge there are no transistors on this board.

[VanillaSlicePie]

Update; Well the guy at Vishay technical support was extremely helpful. Emailed me schematics of the display board and explained in great detail why and how this board failed. My one is an early version so numerous components failed when I connected the power connector to display board when machine was energised. They added a diode to prevent this but was a fail which they admitted. I had performed this task many other times, so that’s what had me puzzled.
I asked him if it was okay to share this info and the schematics if anyone requested. After a week with no answer, here it is.
Never connect power connector to display board when machine is energised. More the wiser...
Thanks for help Mr Strangeways.

[ddstoys]

That’s great that they took the time to get back to you specially on such an old item. 

  And yep they hate being changed while powered on


Sent from my iPhone using Tapatalk

[Strangeways]

Update; Well the guy at Vishay technical support was extremely helpful. Emailed me schematics of the display board and explained in great detail why and how this board failed. My one is an early version so numerous components failed when I connected the power connector to display board when machine was energised. They added a diode to prevent this but was a fail which they admitted. I had performed this task many other times, so that’s what had me puzzled.
I asked him if it was okay to share this info and the schematics if anyone requested. After a week with no answer, here it is.
Never connect power connector to display board when machine is energised. More the wiser...
Thanks for help Mr Strangeways.

That is absolutely incredible that they got back to you on that issue. Amazing ! Thanks for sharing the feedback.