Macintosh TV - Normal Chime then Immediate Death Chime

[facenda]

Hey all,

Trying to bring this Mac TV back to life. I had to jumper the Cuda just to get it to soft power, now it does and then gives the normal chime and then an immediate death chime, and stays on a gray screen. It has been recapped, ROM and RAM SIMMs cleaned and re-seated, but I can't get it to do anything different.

I tested the Mac TV chassis with an LC575 board, and it runs fine in there.

Any ideas on this one?

 

[Byrd]

Hi facenda,

An immediate death chime after the bong usually comes down to bad onboard RAM; does it do the same with the RAM stick removed?

In your pic, the onboard RAM module around U11 and UG9, UG10 look pretty cruddy - deep clean time around those areas and the other RAM modules.

 

[facenda]

I cleaned up the area around the onboard modules, and re-flowed all of them, but no change. The behavior happens without a ram stick, and also with a known working stick.

 

[MAC007]

I got one in with the same issue right now!

Mine was previously re-capped and washed in alcohol by someone. I just replaced the common caps with fresh tantalum capacitors.
Death chime persists.

I'm going to scrub it and ultrasonic clean it to see if it gets any better.
Otherwise if it doesn't, I guess I'll have to replace the on-board RAM...

I do have an identical Logic Board that is working to compare with luckily...

I'll report back if I figure it out.

**edit**

I forgot to mention I tried the ROM's from the other Logic Board, the issue persisted!

 

[facenda]

Let me know how that ultrasonic clean goes, I don't have an ultrasonic cleaner yet but was considering one.

At this point I am suspecting bad RAM or the CUDA, since I still have to jumper pin 27 to 5v to get soft power at all.

 

[bibilit]

Can also be the Egret chip or a bad trace.

 

[MAC007]

***Update***

- Gave the logic board a thorough scrub and ultrasonic cleaning, no change at first.
- Pulled a few suspect ICs with dodgy-looking legs (U22, U28, U29). After that, the board wouldn’t power on. Turned out Y1 didn’t appreciate the heat; replaced it.
- Tip: pull Y1 before working near U29.
- With Y1 replaced, the board powered up and the death chime disappeared. Looks like refreshing U29 was the real fix.

My outcome:
- This one turned out to be straightforward. It’s been back in the chassis all morning and running solid. Will be stress testing it for a few days before I let it go.

 

[facenda]

Glad to hear it worked out! Did you have a replacement for U29 or did you just clean it and re-attach?

 

[MAC007]

I'm glad it did too! I really thought this one was going to be difficult.

I did not replace the chip U29, I pulled it, burned all the legs with fresh solder and flux, cleaned it with alcohol, then solder wicked the U29 landing pads, checked and confirmed continuity for each line going to their respective locations, then re-installed the freshened up U29 chip. I really think something was not connecting with it, due to the old capacitor leakage from C13 & C184....

 

[MAC007]

Good luck with yours! Let me know if you need any help with it, as I have these Macintosh TV boards here for about another week to compare with.

 

[facenda]

I pulled the Cuda (U29), cleaned, and refreshed it, but no change. The pad for pin 28 of the Cuda is completely gone, any suggestions on where I could jumper it to? Schematics of similar boards suggest it pins out to XFC, but I am unclear what that is

 

[MAC007]

Which pad is missing? I am not sure which one is pin 28. Take a picture and let me see.

 

[facenda]

Pin 28 is the sad pin at the top left of U29, with nowhere to go.

 

[MAC007]

That one is showing continuity going to the bottom side of the board. C135. Jumper it to the red arrow in the photo. (for testing)

 

[MAC007]

Confirm continuity between the via in the photo (red arrow) and C135. If it tests positive, solder directly to that via.

 

[facenda]

Well, I made a bad mistake while soldering and yanked a couple pins out of the Cuda. The only way this board gets salvaged is in the hands of someone far more capable than me.

Thank you all for the suggestions and help, I appreciate it!

 

[Byrd]

@facenda all is never lost - I would recommend you practice soldering, making trace wires using junk boards. The image you referenced from desoldering U29: the solder looks too cold, or you need more flux.

 

[facenda]

Thanks for the advice, this was my first go at repairing a board like this. Probably should have tried something that wasn't so rare!