Tech: Installed FPU in E-matrix and A1200 no longer boots

[save2600]

Sigh. Here we go. Received a known working FPU today, along with its crystal and its socket. Did a fine job soldering and made sure there were no shorts. My E-matrix board seems to be "special" in that it was either missing components or had too many. Comparing my board with one from BBOAH, I have rectified those scenarios. To the best of my ability anyway. Not sure if I have the exact value needed for the surface mounted diode above and to the right of the FPU's crystal, but I tried 3 and they all produced the same results.

Long and short of it: computer does not want to boot with the FPU installed. Only components missing from my board compared to the BBOAH's board is the circuitry for the SCSI side of it. I don't care about SCSI right now, just want this board to work happily with the FPU.

Anyone know what gives? I've attached 2 pics. The BBOAH's board will be on top and my board below. FPU I received is labeled: XC68882RC50A. My CPU reads: MC68030RC40B. They are both clocked at 40mhz. There wouldn't be an incompatibility here, would there??

[Homer]

I would hazard a guess that you have fried every chip on the pcb by placing it on a towel. The static will probably have blown the lot.

C'est pour la poubelle maintenant !

[save2600]

What towel?  :-)

Again folks - the system boots perfectly fine without that frickin' FPU  :-(  

Card will probably be more stable now that I've touched up the cold solder joints on the connectors.

[rkauer]

 Bad FPU, perhaps?

[CLS2086]

or a remarked FPU that can't handle 50 Mhz...

check if you have no pin bent, and try to desoxydate the FPU support.

[cantido]

Homer wrote:
I would hazard a guess that you have fried every chip on

I cant see much CMOS logic from the photo... 74F series are TTL if I remember correctly and shouldn't be as easy to kill with ESD.

So, no, it wouldn't be every chip.

[Homer]

It's a general observation that comes from seeing many pcb's sat (usually) on carpets both here and Ebay, and people telling us they don't work properly.

In my work as an electrical/electronics Engineer working on trains in the UK, I managed to measurably reduce random failures on one fleet by instructing technicians in anti-static procedures.

Would you buy a pcb photographed on a towel ? Why spray a towel with anti-static juice when you could just sit the pcb on an anti static bag that it should be stored in if not fitted to the computer ?

This is getting off topic, I have no interest in flaming the owner of the board, but don't expect myself to be flamed for highlighting bad procedures.

Good luck with the FPU  :-)

[Ideal]

Received a known working FPU today, along with its crystal and its socket.....
Only components missing from my board compared to the BBOAH's board is the circuitry for the SCSI side of it.

I believe you are mistaken in this assumption.

If you look at the image on BBOAH, to the right hand side where the jumpers are you will see that on the PCB it says JP1: FPUSPEED and JP1 is then in fact not a jumper, but in fact a DIODE solder onto the board.
I believe you will not be able to work an FPU in this board without installing the appropriate diode as pictured on BBOAH.

[wolfchild]

Not sure if I have the exact value needed for the surface mounted diode above and to the right of the FPU's crystal, but I tried 3 and they all produced the same results.

The part you have fitted is a Tantalum capacitor (10uF, 25V) and not a diode.

Are you sure what the original part shown on the BBOAH picture really is?  I mean, is it a diode or a Tantalum cap?  You might want to double check what should go there and not to power up with that capacitor in place until you're sure.

Be warned that Tantalum caps very often fail explosively and without warning if they have a wrong polarity voltage applied to them.  If indeed a diode was supposed to be there, then that Tantalum cap is getting a reverse voltage and is very likely to end up in fireworks if you power up that board for any length of time.

I hope you do get it working soon!  You seem to be pretty close, but be careful about the component values.

Good luck!

[Ideal]

Don't distract from the diode that should be on the right, next to the jumpers.

[cantido]

Homer wrote:
It's a general observation that comes from seeing many pcb's sat (usually) on carpets both here and Ebay, and people telling us they don't work properly.

mmm if they've taken a photo of the pcb to show us when it doesn't work.. wouldn't it have already been broken before it went on to the carpet (or similar) to be photo'd?

I wouldn't buy anything off ebay that wasn't guaranteed against it being DOA unless I was buying it for spares.

In my work as an electrical/electronics Engineer working on trains in the UK

Working with higher voltage -- CMOS -- logic? You'd think the stuff used on trains would be a little be more rugged considering it's going to get shaken around, covered in crap etc.. A lot of stuff has protection against ESD up to 15kV or something these days.


Anyhow.. I would have said taking a soldering iron to the thing would have been more of concern.

[save2600]

@ ideal:

JP1-JP3 are jumpers under that cap. The diode to the left is what was missing.

I've soldered a diode and desoldered it to no avail. I've traced the connection of that diode back to the SCSI circuit. Should not affect the FPU, but I installed on there anyway. Same goes for the cap.

@ wolfchild:

I've added three tantalum caps to no avail. Might not have been the incorrect values, but I tried three. Polarity was observed, so nothing blew up! lol  Even moved the tantalum cap to the lower left of the board to the place in question. Nada. Added a diode to the place in question as well to no avail. The pic from BBOAH looked like a diode to me. Upon testing it, it sure does not test like a diode. SO... lesson learned here. Why they'd make a  surface mounted tantalum cap look like a diode is beyond me (black w/ grey band). Course, didn't see the typical 1N00X markings, but...  

Maybe I should try spraying it down with WD-40 next?   LOL!

I'm totally out of ideas here. Either that FPU is blown and is causing the computer NOT to boot or something else is wrong here.

Card still works without the FPU of course. I'm not sloppy with an iron and I'm not in the habit of zapping out I.C.'s.

Thanks to all for the productive suggestions.