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LC575 No Screen and Death Chimes

Nev

Member
I am determined to build a working LC575 out of all the pieces I have. What do I have ? 2x CRT's and bodies incl HDD's, 2x Logic Boards, 3x Analogue Boards. I have recapped both Logic Boards, one of the Analogue Boards (big job) and ultrasonic cleaned with Isopropyl Alcohol rinse of all boards. I created a new 4.5v battery from three 1.5v batteries and the old cable. I've tried all the different combinations together to try and get one working but nothing. My sense is that both the Logic Boards are at fault. One Logic Board gives me startup chime followed Death Chimes (two sets of tones) and a blank screen. I can hear Hard Drive activity. The other Logic Board gives no chimes, blank screen and some Hard Drive activity.

Apart from re-capping, what else can you do with these logic boards ? Are their any other components that commonly fail or testing that can me done. I've tried starting with CMD-ALT-P-R and also tried booting from CD with no success. Any suggestions as I'm at a dead end !!!

PXL_20210806_093302765.jpg
 

robin-fo

Member
I have a SE which had a black screen but was otherwise working properly. Recapping the analog board wasn't successful, I had to replace some high voltage diodes and transistors to bring it back to life. This would certainly not resolve your death chime issues, but might at least give you some kind of image on the screen...
Are you certain that your RAM is properly installed?
Good luck! :)
 

Nev

Member
Thanks, I've pulled out and put back in the RAM a couple of times and have two sets of RAM so I could try both. As you suggest I'll have to start going though other components one by one until it works. I had a couple of spare TDA4605's so replaced those but no luck. I think diodes and transistors will be next.
 

bibilit

Well-known member
No LC575 myself, but probably the Logic Board has an Egret chip.

Heavy failure on this item and responsible for a lot of issues.
 

Nev

Member
No LC575 myself, but probably the Logic Board has an Egret chip.

Heavy failure on this item and responsible for a lot of issues.
Thanks, now for the fun task of trying to track one down. They appear to be Apple specific.
 

bibilit

Well-known member
Yes I agree but usually just heavily contaminated or poor connection.

Lifting the chip and soldering back after a good cleaning can restore properties.
 

Nev

Member
Thanks, I removed, cleaned and re-soldered the Egret chip on both boards. Both still act exactly the same as before. It's a process of elimination and that's another one I can tick off.
 

Bama

Member
Hi Nev,

I am working in the same circumstances. I am hoping we might work together.

Which IC is the Egret?

Following recap of my LC575’s LB and AB (and U/S cleaning of the LB and confirming the AB works with my LC520), I have found potential problems on my logic board:

  1. the memory chip (at U10) has several open internal circuits. I still hear death chimes after replacing it.
  2. I have found the solder pads for the onboard memory ( at U10-13-14-16-18-22-24 & 25) have continuity between logic board pads 16 (IC pin 26 = GND) & 20 (IC pin 22 = output enable). My LC520 has the same onboard memory and it does NOT have continuity between those pads.

Do you mind checking to see if you have continuity between pads 16 and 20 for an onboard memory IC on your logic board? I am thinking this may be a short on my LB that I need to continue hunting for.



Thanks,

Bama
 
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