Korg Forums

Hello I recently purchased a Korg PA800 which has a screen flickering issue, the gentlemen I bought it from said he replaced the LCD display and that did not fix the issue. What happens is that the display flickers off and on, the keyboard functions fine except for the flicker. I have taken everything apart boards and all and cleaned all the cable contacts and the ribbon cable ( checked for continuity from both ends) for the display several times. At first I got It to work for a while and thought it was the flat ribbon cable but then the issue came back.

When the display goes out obviously there is only a blue screen, when I tap lightly or pull on the ribbon or main cable to the inverter it seems to disturb something then it comes back on for a bit then goes out. I have checked the voltages from the power supply all seem to be good. Nothing has jumped out at me. I even removed the ram and booted up without but still same thing.

I also reloaded the software but still nothing. I am unsure what the issue is, whether the Mainboard or the CPU board . which component is failing or not latching would be of interest. Anyone have any idea as to what the root cause is? I have read many posts here and outside this forum but did not find anything relating to this type of issue. I do not mind removing and replacing the IC chips if need be. Thanks for your help in advance and sorry for being long winded.

Hi Mike - the ribbon itself may need replacing.

I had different problems with my PA1XPro and took it apart and reseated everything - problem was fixed but it is possible that the ribbon or its connectors may be dodgy.

If the problem is easily reproducible then it may be worth getting a quote from a service centre.

Good luck

Pete

karmathanever wrote:Hi Mike - the ribbon itself may need replacing.

I had different problems with my PA1XPro and took it apart and reseated everything - problem was fixed but it is possible that the ribbon or its connectors may be dodgy.

If the problem is easily reproducible then it may be worth getting a quote from a service centre.

Good luck

Pete

Hello thanks for reply, as you noted that was my main focus of a cable not making good contact. Then I ruled out that since I made sure there was good continuity from one end to the other end while seated on the boards.

I went ahead in decided to meter the CPU board top and bottom for resistor and capacitor issues, this took about 2 hrs under magnification.
I noticed that I had an RA ( resistor array) bank which was supposed to read 100 ohms, one of the resistors was reading 2.1K ohms, I said bingo there is an issue. Also there were two resistors that were supposed to measure 300K were actually at 200K and 120K ( I have to figure what they do). After this I pulled the SM and looked up the CPU schematics and sure enough the RA was in the circuitry of the LCD display ( IC5 on the board). after poking at theta resistor for a while I finally managed to get a reading of 130 ohms from the 2.1 K. I placed back in the unit and behold everything came to life on the LCD display. I did have the blue screen with no display just the back light when the flickering stopped. So the resistor not making good contact ( for now) was where the flickering coming from.

I believe that the issue with the blue screen of death is simple to fix as long as the IC 5 is not faulty and there are no PSU issues. This is minor dollar value fix and not having to spend hundreds of dollars on boards. I will post up pictures of the location when I get a chance. I also need to go back and solder down that resistor for good and find out what the other two resistors function are. It was late at night when I powered it up to check the LCD.