Any thoughts on my SE/30

[cannfoddr]

I’ve been working on this SE/30 board for some time and am pretty stuck at the moment.

Board has been recapped. Original problem was no VSYNC. I fixed this by replacing UE8, UF8. I now get the screen shown in the photo. I believe, based on HDD activity that the machine is booting fine, but with no video.

If I swap logic board with another SE/30 the problem moves with the logic board. Other machines board in this chassis works fine so I am ruling out analog board issue. I have swapped RAM and ROMs.

i most recently removed, cleaned, and re-soldered ALL the UE chips with no improvement. I have been looking for broken traces but so far can’t find any on the video circuit.

 

[RetroViator]

Sorry if this is too basic, but have you swapped out the RAM?

 

[cannfoddr]

“I have swapped RAM and ROMs…”

Yes. I’ve also tried a different video ROM. It doesn’t look like the images of semisamac that I have seen elsewhere

 

[Kai Robinson]

Hi @cannfoddr ! This looks suspiciously like a video RAM failure - 1/2 the screen frame isn't being drawn - i'd recommend desoldering the chips at UB10 and UB11 - those are the 41264 DRAM's for the video system. I'd also check UF8 - the 74LS166.

 

[cannfoddr]

Hi @cannfoddr ! This looks suspiciously like a video RAM failure - 1/2 the screen frame isn't being drawn - i'd recommend desoldering the chips at UB10 and UB11 - those are the 41264 DRAM's for the video system. I'd also check UF8 - the 74LS166.

UF8 replacement originally restored VSYNC - that’s been done along with a UE8 replacement for good measure.

i will take a look at UB10 and 11. I have another board (not working) that I could use as a donor if needed.

I have a scope available but am a complete novice with it - could this help me diagnose the RAM?

 

[Kai Robinson]

This datsheet might help - start by probing the address lines and see if there's any wierdness

 

[cannfoddr]

Hi @cannfoddr ! This looks suspiciously like a video RAM failure - 1/2 the screen frame isn't being drawn - i'd recommend desoldering the chips at UB10 and UB11 - those are the 41264 DRAM's for the video system. I'd also check UF8 - the 74LS166.

UF8 replacement originally restored VSYNC - that’s been done along with a UE8 replacement for good measure.

i will take a look at UB10 and 11. I have another board (not working) that I could use as a donor if needed.

I have a scope available but am a complete novice with it - could this help me diagnose the RAM

Hi @cannfoddr ! This looks suspiciously like a video RAM failure - 1/2 the screen frame isn't being drawn - i'd recommend desoldering the chips at UB10 and UB11 - those are the 41264 DRAM's for the video system. I'd also check UF8 - the 74LS166.

 

[cannfoddr]

@Kai Robinson I’ve just checked my schematics. UB10/11 are sound chips. I think you must mean UC6/7 they are shown as Video RAM on the schematics?

 

[Kai Robinson]

Argh, yes, sorry the silkscreen in that area is rather cramped.

 

[cannfoddr]

So I’ve had a good play around with the scope. I can’t see anything horrendous. Whilst playing around with the various pins on UC7 I noticed I can change the displayed image in a pretty persistent way - it seems to persist across reboots! Plan A now is to get some sockets and some spare UC6 chips (if possible) and start by replacing UC7

 

[fred1212]

I think my SE/30 is in similar territory. Chimes and boots(can see bluescsi flashing) . Originally no screen but I've removed and cleaned UE8 LS166 and UF8 LS393 both had cap goo under and now I get what is shown in pics. What to check next?