-
Updated 2023-07-12: Hello, Guest! Welcome back, and be sure to check out this follow-up post about our outage a week or so ago.
SE/30 - Is 74ALS166 a Replacement for UE8 (LS166D)?
- Thread starter asapreta
- Start date
techknight
Well-known member
Nothing in that video circuit is going to make it boot. Need to give up in that area.
Time to start looking at ROM/RAM especially if you get no chime and that pattern.
If the battery had leaked in ANY way shape or form in that motherboard, its likely eaten away a via/trace going to the ROM and THAT will stop it from booting. Plus there is a cap that sits right there and leaks, does the same exact thing.
If you get slow chimes, its because RAM addressing lines are broken, or the 74F253 muxes are bad.
Time to start looking at ROM/RAM especially if you get no chime and that pattern.
If the battery had leaked in ANY way shape or form in that motherboard, its likely eaten away a via/trace going to the ROM and THAT will stop it from booting. Plus there is a cap that sits right there and leaks, does the same exact thing.
If you get slow chimes, its because RAM addressing lines are broken, or the 74F253 muxes are bad.
Last edited by a moderator:
No it doesn't chime at all.
The board is recapped and the tracers for UE8 are good.
I couldn't just find where is the CLOCKIHB signal (pin 6 of UE8) but I think it is grounded.
No I get no chime.
There was no battery leak.
I replaced the caps near the ROM SIMM and RAM banks. So, I may still have a line broken there, mostly near ROM?
Thanks for helping me.
I have a working SE/30 board and did a test to try to narrow the problem.
If I remove the RAMs and try to boot, this working board chimes and give me the same pattern as the defective one on the screen.
With the RAMs but without the ROM SIMM the boot is the same as the defective.
So I may need to check if there are any broken traces leading to the ROM.
Which usually fail in this case (near LS166 - UE8) area??
This board worked for a while before it crashed. It made a sound like a crackle and stopped working and I saw how destroyed was LS166D.
I recapped it and now was able to get this ALS166.
Thanks for the help.
If I remove the RAMs and try to boot, this working board chimes and give me the same pattern as the defective one on the screen.
With the RAMs but without the ROM SIMM the boot is the same as the defective.
So I may need to check if there are any broken traces leading to the ROM.
Which usually fail in this case (near LS166 - UE8) area??
This board worked for a while before it crashed. It made a sound like a crackle and stopped working and I saw how destroyed was LS166D.
I recapped it and now was able to get this ALS166.
Thanks for the help.
techknight
Well-known member
You have a broken trace to the ROM SIMM.
More rarely, you could have a shorted data buss from solder falling through the vias and smearing to the adjacent vias, and it will do the same thing. You will need to flip the board over and inspect all the areas where the caps are and make sure there are no crossed-over solder. This occurs in the sections your heating up and reworking to replace caps or chips. If you used a heatgun, this happens.
Once you have an eagle-eye for that, youll see it quickly. If that fails, you can meter all the A and D lines against each other for shorts. If that checks ok, then you definitely have a broken ROM trace. you COULD have a bad CPU, but thats really really rare. I have seen it once though with someone elses board, What gave it away was when scoping the bus with the ROM simm inserted, all the Data lines dropped down in voltage to around 2.5v or so which i knew then the CPU was toast.
More rarely, you could have a shorted data buss from solder falling through the vias and smearing to the adjacent vias, and it will do the same thing. You will need to flip the board over and inspect all the areas where the caps are and make sure there are no crossed-over solder. This occurs in the sections your heating up and reworking to replace caps or chips. If you used a heatgun, this happens.
Once you have an eagle-eye for that, youll see it quickly. If that fails, you can meter all the A and D lines against each other for shorts. If that checks ok, then you definitely have a broken ROM trace. you COULD have a bad CPU, but thats really really rare. I have seen it once though with someone elses board, What gave it away was when scoping the bus with the ROM simm inserted, all the Data lines dropped down in voltage to around 2.5v or so which i knew then the CPU was toast.
Last edited by a moderator:
Bolle
Well-known member
Are you getting slow chimes of death? In this case as techknight already said check the RAM and the 74F253 muxes as well as the address lines to said muxes and the address lines from the muxes to the SIMMs.
You can check the muxes by removing the ROM and RAM and powering the machine on. The CPU will enter a loop of cycling the address bus and you can measure the outputs of the 253s as all of them will be driven in this state (you can even use a multimeter in frequency mode if you don't want to get the scope out for that) One or two outputs will have frequencies in the low Hz range (even below 1Hz if I remember right) that a multimeter might not pick up though. I use the meter in voltage mode for those as you can see it jumping between 0 and 5V then.
You can check the muxes by removing the ROM and RAM and powering the machine on. The CPU will enter a loop of cycling the address bus and you can measure the outputs of the 253s as all of them will be driven in this state (you can even use a multimeter in frequency mode if you don't want to get the scope out for that) One or two outputs will have frequencies in the low Hz range (even below 1Hz if I remember right) that a multimeter might not pick up though. I use the meter in voltage mode for those as you can see it jumping between 0 and 5V then.
