Lines on the SE/30 screen after recapping

[Minja]

Hi,

just done a recapping and the machine starts up properly with a chime and everything seems to be working fine. But there are vertical lines on the screen that were there even before the recapping. Have no idea where to look.

Thanks in advance!

Cheers!

 

[cheesestraws]

They're every 8 pixels, which means that one bit of each byte of VRAM isn't making it back out again. Probably some damage or corrosion somewhere around the row of chips UA8-UG8, they'te notorious for getting knackered by any corrosion going around.

 

[joevt]

If that's a black and white 1 bit graphics mode, then there's a problem with an 8-bit bus so ignore any buses or chips that are 16 or 32 bits.

It looks like a problem with the 4th pixel from the left.
That is bit 4 (bit 0 is the 8th pixel) for 8-bit buses.
Bit 12 and 4 for 16-bit buses.
Bit 28 and 20 and 12 and 4 for 32-bit buses.

The problem is with the 5th pixel from the right. That is bit 4 for 8,16 or 32 bit buses (since the width of the screen in pixels is usually a multiple of 8 or 16 or 32 pixels).

 

[Minja]

They're every 8 pixels, which means that one bit of each byte of VRAM isn't making it back out again. Probably some damage or corrosion somewhere around the row of chips UA8-UG8, they'te notorious for getting knackered by any corrosion going around.

Thanks for the reply. Ok, I’ll take a look at the joints on all of them. Especially those ones close to c2.

Is it a good idea to refresh the soldering joints on them?

 

[Minja]

Update after some serious tinkering - checked all the contact paths on the most leakage exposed u_8 chips and found that path from pin 10 on UE8 had no contact with pin 2 on UC6.

Soldered a wire to connect them and now it’s working. So far so good. Surely some other things might pop I as a result of cap juice eating up stuff.

Thanks for all help!

 

[joevt]

Update after some serious tinkering - checked all the contact paths on the most leakage exposed u_8 chips and found that path from pin 10 on UE8 had no contact with pin 2 on UC6.

Makes sense. UE8 has an 8 bit bus. Bit 4 is VID(4) which is pin 10 on UE8 and pin 2 on UC6.

 

[cheesestraws]

Update after some serious tinkering - checked all the contact paths on the most leakage exposed u_8 chips and found that path from pin 10 on UE8 had no contact with pin 2 on UC6.

Yeah, that's pretty typical. Glad you got it sorted!

Surely some other things might pop I as a result of cap juice eating up stuff.

Yeah - once you've got it clean then it should be largely stable but the act of cleaning can dislodge stuff that was marginal.