Quadra 840AV - chimes ... kinda ...

[ApfelKlassik.de]

Hi folks,

Question, did anyone ever hear/see the phenomenon in the attached video? And has some ideas?

Board did get recapped, washed ... "good known" RAM got used. Traces look all fine.

But on startup only a chopped of chime of less than 1/2 (see attached link) ... every 50 tries or so a full chime but no full boot.

Somehow my suspicion is towards the PSU - even if it delivers stable -12V.

New video by Markus W.

photos.app.goo.gl

 

[ApfelKlassik.de]

Update - no change with a new PSU ... so it must be an issue somewhere on the Logic Board

 

[ApfelKlassik.de]

Noone any idea ?

 

[Branchus]

The 840AV is a nightmare and I hate working on them. They have tiny little traces with a weak point just as the trace becomes a pad under a component. I have worked on 840AVs that look pristine, only to find dozens of broken traces around and under components. I can't say I've ever experienced the exact issue you mention, but it is probably caused by a broken trace somewhere.

I realise that's not much help, sorry.

 

[ApfelKlassik.de]

Thanks a lot for your answer, Bruce @Branchus .

I am currently contemplating getting an Ultrasonic Cleaner (thanks for the review ) as next step - still hoping I can avoid microscopic trace surgery.

General interesting question would be, what the system is actually starting to do after starting to play the chime.

 

[Mac84]

I also echo the advice of Bruce, there must be a bad trace somewhere. At least that's my thought. The traces on those boards are silly thin and fragile.

Also, because of this, I'd caution the use of an ultrasonic cleaner. You can use it, just be aware that in some rare cases it may damage weak traces that are hardly holding on as it is.

I'd start by trying to look at each capacitor and start with a 1-2 inch radius around them. That will often be where the breaks are. Use magnification, as it'll be impossible to see otherwise. Good luck!

 

[ApfelKlassik.de]

Thanks Steve @Mac84 !

One thought crossed my mind today - could this be one of the rare occurrences, where capacitors with a "wrong" (too low) ESR or ripple could be the culprit?

 

[Mac84]

Thanks Steve @Mac84 !

One thought crossed my mind today - could this be one of the rare occurrences, where capacitors with a "wrong" (too low) ESR or ripple could be the culprit?

I don't think that would be the case? But my recapped 840AV seems to be perfectly happy with good quality (KMET, etc) tantalum capacitors.

Have you tried the board without any drives or accessories plugged in? I know it's a long shot, but I think I hear the hard drive in your video clip. I'd remove all VRAM and use one RAM module. If your Quadra doesn't have the ROM built-in, ensure you clean the contacts on the ROM SIMM.

I'd also triple check any recapping work to ensure the caps are connected properly, there aren't any traces exposed under them, and that the surrounding traces are okay. Good luck!

 

[ApfelKlassik.de]

Yep, of course tested without anything ... only didn't unplug the HD from power .

It's getting interesting - I decided to replace all caps again ... started near the CPU working left to up ... testing after 2 replaced ones.

So, after the first four - same behaviour ... then the next 2 ... replaced - and now new chime at all. The traces around are looking good - only one of the 3 Cs in the areas have traces running beneath them, also looking good. (Loupe - no microscope)