Macintosh LC 475 chimes, but no video

[joshc]

@pedroskw I think in my last post I asked about your PSU voltages, did you check them? Use a multimeter on the pins on the power connector while its pluggd in/switched on to see what voltages are there.

If PSU is recapped and outputing the right voltages, and you still get no start with good PRAM battery, then the Egret is probably stopping it from starting. That chip is essential to the start process. With no start you won't get the floppy intialising either, so it matches with your symptoms.

Edit: Just seen you mentioned checking in another machine, so I am going to guess Egret issues are stopping your board from working. I've had this happen with a 475 before. The Egret is a custom chip so a new one cannot be ordered. You have to pull one from another board. You could try desoldering/cleaning and resoldering it though.

 

[pedroskw]

@pedroskw I think in my last post I asked about your PSU voltages, did you check them? Use a multimeter on the pins on the power connector while its pluggd in/switched on to see what voltages are there.

If PSU is recapped and outputing the right voltages, and you still get no start with good PRAM battery, then the Egret is probably stopping it from starting. That chip is essential to the start process. With no start you won't get the floppy intialising either, so it matches with your symptoms.

Edit: Just seen you mentioned checking in another machine, so I am going to guess Egret issues are stopping your board from working. I've had this happen with a 475 before. The Egret is a custom chip so a new one cannot be ordered. You have to pull one from another board. You could try desoldering/cleaning and resoldering it though.

yes, already tried to unsolder clean and resolder. the pcb is clean and has no signs of oxidation. There are no datasheets of this egret chip? is an apple top secret?

 

[pedroskw]

without the egret the mac would not make sound on boot, so I thought that it was not the cause. I found, in the mac roms collection, the dumps of some egret/cuda chip, how did they get them? I don't think they are simple roms, they should also incorporate the rtc and something else

 

[joshc]

@pedroskw You didn't mention sound before, so I assumed there wasn't any. So it's chiming normally, just no video?

 

[pedroskw]

@pedroskw You didn't mention sound before, so I assumed there wasn't any. So it's chiming normally, just no video?

Yes it's chiming normally, but no video and no floppy/hdd activity

 

[joshc]

Tried looking at voltages, not just at the power connector but in various places on the board? Sounds like 12V might not be getting where it needs to?

 

[Plasticoat]

Did anyone ever solve this issue, I have a board that exhibit the same issues

 

[Phipli]

Did anyone ever solve this issue, I have a board that exhibit the same issues

Do you have a good battery in it?

 

[pedroskw]

check the address and data bus with the memory, on mine there was a broken track

 

[Plasticoat]

Yea battery was good, brand new , I’ll check the traces thanks for the info