Help with LCII Repair

[ravuya]

Wow! I did not know this. I thought it would not be possible to dump it from the Mac.

Maybe the Egret is the same as one of these 6805 MCUs, and if so, we could burn another: http://www.bitsavers.org/components/motorola/6805/Single_Chip_Microcontrollers.pdf

The Egret has 28 pins and evidently 4.25 kB of ROM, judging from the ROM dumps. None of the MCUs in that list seem to match. Some have 4.5 kB of ROM though. 

I'm really curious about this too - I had thought the EGRET was more custom than it actually is, but now that I look at the ADB technotes it does seem to be a 68hc05 microcontroller (looks like it's even inside CUDA on the PPCs). I don't know if the pinout is feasible or if it's a custom package that would require a wiring adapter.

 

[bibilit]

Curious also. 

I have been dealing with a stubborn LC. 

Will boot to the question mark but not from a good hard drive or from a floppy. 

Then, will not boot at all. 

In the end was the Egret, replacing it solved both issues. 

 

[joshc]

So far I buzzed out traces for pins 1-14 (one side, all I had time for) and so far it appears the traces are intact. However: I did not check 12 or 13: on the schematic, 12 leads to RESET (is that just an 030 pin?) and to some sort of delta with lines that I am not familiar with diagram-wise. That makes me lean towards the EGRET. I found this possible supply of them, but I am not sure if it it the usual Chinese knockoff stuff. I don't care what vintage it is as long as it works.

https://www.joybuy.com/product/2221993.html

Is this same chip used on the LC 475?

I have an LC 475 with similar issues to the ones you described in this thread, it's recapped and been cleaned several times but doesn't output video and the chime is garbled, I have tried every avenue of diagnosis/troubleshooting so I am wondering if an IC is at fault.

 

[bibilit]

Yes, same chip.

Have you got a good battery ?

the LC 475 won't have video output without a fresh battery.

 

[joshc]

Yes, same chip.

Have you got a good battery ?

the LC 475 won't have video output without a fresh battery.

Yes, a new battery outputting 3.6v. Even tried swapping VRAM, RAM, CPU and PSU all with known good ones which is what lead me to think its a faulty IC.

Where did you get a replacement EGRET chip from?

 

[bibilit]

from a battery destroyed board.

 

[LaPorta]

Ok, well, to finally resurrect this thread...

I got a spare EGRET from TechKnight a few months back. Been so busy, I have not been able to get around to trying this at all. Patched some things up, desoldered old EGRET, installed new EGRET, and there is at least some sort of life. Scratchy sounds at power on, goes to a gray screen (which is a big difference vs. no video before). However, the screen sometimes "bounces" in and out, like it is intermittent. Then, sometimes there is a horizontal bar pattern on the screen. No attempt to boot. Appears that the intermittent issue goes away and the screen stays on with time. All sounds to me like some sort of intermittent trace, but once the thing has heated up and no longer crackles, why would it not attempt to start if the trace is connected? Is it more than one? I suppose I can check the EGRET pins on the scope again as mentioned above.

Tagging in @Scott Baret and @techknight so that they finally know this didn't go nowhere and I didn't just forget or lose the stuff!

EDIT: Following Zane's earlier suggestion, the last thing I was able to check tonight was Pin 12. He said this should be low when there is no "brownout" condition. Well, on startup it consistently reads 4.4v, perhaps that indicates something.

 

[techknight]

My LCIII does this when I first turn it on. the screen scrambles, shakes and wobbles for 15 seconds or so before it stabilizes out. 

Never did figure it out. But the machine worked fine otherwise. 

 

[LaPorta]

Regrettably it doesn't stablize. The crackling coincides with lines on the screen. Now, I am no longer getting the gray screen, but no crackles, either. It sounds like this would be a fruitless hunt-and-seek deal. I wouldn't even know where to start. I give you all sorts of credit for getting that EGRET off....the residue left on there is insane.

 

[techknight]

Regrettably it doesn't stablize. The crackling coincides with lines on the screen. Now, I am no longer getting the gray screen, but no crackles, either. It sounds like this would be a fruitless hunt-and-seek deal. I wouldn't even know where to start. I give you all sorts of credit for getting that EGRET off....the residue left on there is insane.

Yea it was no fun. but at least the EGRET is working in this instance, to a degree. but it came from a board that was just as bad, if not worse than yours.