SE/30 video distortion (boots okay)

[elemenoh]

This SE/30 MLB displays distorted horizontal and vertical video but does boot okay. The board has been recapped and most traces for video have been tested. It's also had UA8, UB8, UC8, UD8, UE8, UF8 and UG8 replaced. I swapped in known-working chips into UE6, UE7, UG6, UG7, and UI6. I sprayed the video ROM and socket with contact cleaner. Known-good RAM is installed.

I tried applying pressure to the video RAM chips at UC6/UC7 while the machine was on, but the symptom didn't change.

What would be the best thing to try next other than more trace testing? Swapping video RAM? If so, is there a modern and available replacement for those chips?



View attachment IMG_2281.mov

 

[Bolle]

I had a board with a similar issue and it turned out to be an address line going to the VRAM muxes with intermittent contact. Took me quite some time to find it because it tested good a couple of times when checking with my multimeter.

 

[elemenoh]

I tested the following again with a multimeter and all seem okay. I don't have a scope so can't test live.

• A0: UD8 pin 4 to UK6 pin 10
  
• A1: UD8 pin 12 to UK6 pin 9
  
• A2: UC8 pin 4 to UK6 pin 8 to ROM pin 4
  
• A3: UC8 pin 12 to UK6 pin 7 to ROM pin 5
  
• A4: UB8 pin 4 to UK6 pin 6 to ROM pin 6
  
• A5: UB8 pin 12 to UK6 pin 5 to ROM pin 7
  
• A6: UA8 pin 4 to UK6 pin 4 to ROM pin 8
  
• A7: UA8 pin 12 to UK6 pin 3 to ROM pin 9
  
• A8: UD8 pin 3 to UK6 pin 25 to ROM pin 31
  
• A9: UD8 pin 13 to UK6 pin 24 to ROM pin 32
  
• A10: UC8 pin 3 to UK6 pin 21 to ROM pin 33
  
• A11: UC8 pin 13 to UK6 pin 23 to ROM pin 34
  
• A12: UB8 pin 3 to UK6 pin 2 to ROM pin 35
  
• A13: UB8 pin 13 to ROM pin 36
  
• A14: UA8 pin 3 to ROM pin 37
  
• A15: UA8 pin 13 to ROM pin 38
  

Since some of the traces under UF8 might have been damaged by the nearby capacitor, I ran wires between the following:

• UF8 Pin 6 to UC8 pin 5
  
• UF8 pin 5 to UD8 pin 11
  
• UF8 pin 4 to UD8 pin 5
  
• UF8 pin 3 to UA8 pin 10
  
• UF8 pin 1 to UA8 pin 6
  

The symptom didn't change. It's still getting distorted video despite booting okay.

Are there other connections I should be testing to narrow this down?