Reversed polarity of power cable!!!

[dino00]

Hello to everyone!

I'm new to to the forum (as far as writing that is, 'cause I've been reading for a while now) and I would like to congratulate everyone for a job well done.

I really hoped that my first post would be different and not as stupid but you know... bad things happen.
Anyway thing is that a couple of weeks ago, I was doing some cleaning inside my beloved A500+. So I disconnected the inside power cable (the little cable that connects to a white connector on the A500+ mainboard), did a bit of cleaning and then I connected it without noticing that its polarity was wrong. When I powered the Amiga up there this sound, quite a bit of smell and the Amiga is now obviously dead.
My question is this: how can I understand what got burned and repair it? What would be the "usual suspects" i.e. the components that most probably got burned? Is a repair a viable solution or should I forget about my glorious A500+?

Thank you all!
Byez!

[recidivist]

Quite a bit of smell tells me it wasn't a fuse.

I'd start looking for a replacement A500+.

About the only electronic components that aren't adversely affected by reversing the power are resistors,fuses,and switches.

[Karlos]

I baked a 1200 motherboard with a dodgy AT PSU once. It didn't smell very good at all.

Only the socketed ROM chips and components not attached at the time (luckily this included the accelerator card and drives) were salvageable.

[banzai]

So I disconnected the inside power cable (the little cable that connects to a white connector on the A500+ mainboard)

Errr. The only power connector I can think of that would be white and on the mobo is the one for the floppy drive (CN12). Connecting this backwards would result in:

* Supplying 12V to the floppy's 5V bus (and 5V to the 12V bus, but that's not a problem here). This means everything you smell is most likely from the bottom of the drive. If this is the case, then replacing the floppy should do it. Now, if you actually moved the connector "down" a pin, then you've got a short to ground, and the PSU blew a fuse or allowed a mobo trace to burn out. Maybe both.

* A possibility of that 12V feeding back on the data cable to Gary and one of the 8520 CIA chips. If this is the case, then replacing Gary, the 8520, and the floppy drive should fix things.

* An even less likely possibility that one of those chips fed the 12V to the rest of the chips on the 5V bus (I've never had any Amiga chips fail in this manner, and I'm not about to test this out). If this is the case, then the mobo and PSU are probably gone.

* The PSU did it's job, and failed before any damage was done to the rest of the system. You can open up the brick, check the fuses, and look for anything smoked. CAUTION: High Voltages Present inside!

My advice on how to go about this:

1) Check PSU for proper voltages (the lighter switching PSUs should have some kind of load on them when testing, the heavier linear models are fine without any). CAUTION: High Voltages Present inside!

2) Remove the floppy and test the system without it in there. If you get the WorkBench prompt, then it's the floppy you need to replace (and see about getting a keyed power plug, too).

3) If a new floppy isn't working, then try the 8520 first, and Gary second (CIAs are known to fail just by frowning at them). If replacing both of them doesn't work, then the whole thing is shot, or you need to find someone more knowledgeable.

banzai

[dino00]

Hi to everyone!

Sorry for taking so long to reply and thanks to everyone for their valuable suggestions.
A special thank you to banzai for the extremelly detailed answer.
Hope you're right mate and the only thing that's fried is the drive.
Going to check the PSU first and then see if I can power up without the drive.
Once again thank you all and I'll keep you informed (if the PSU doesn't blow me up that is  :lol: )
Byezzz

[JimS]

strange... reversing the polarity always works on Star Trek.


I agree with Bonzai though. Probably just the floppy drive fried. When you take it out, look for burned traces, or a residual odor.

[Ral-Clan]

A few years ago I picked up an A500 for $2.50 at a thrift store.  It didn't come with a power supply, but luckily (I thought) I had one for a C-128 that I had picked up for $4 at another thrift store earlier on.

I thought because the C128 and the A500 power supplies looked exactly the same, the would be interchangeable.  

They weren't.

The red LED came on for a second....then something went *SNAP* inside the Amiga 500 and there was a bad odour of burning chips (I hate that smell)!

When I opened the A500 there was actually a piece missing from one of the chips that had burst!

Like any smart Amigan though, I kept the dead A500, knowing that even dead Amigas are useful for parts.  Luckily, it has come in handy (the drive went into my A2000 a few years later).

Moral: always keep Amiga stuff, even if dead.  They aren't making these anymore so spare parts are a finite resource.

[Homer]

Yeah, I would have thought that the main INPUT socket to the A500 would be soldered to the motherboard and not disconnectable, so it could be that you have burnt something else like the floppy drive. Its still likely tho that the consequential high current damaged a pcb trace :-(

[sir_inferno]

JimS wrote:
strange... reversing the polarity always works on Star Trek.

that's cause you not only reverse the polarity, but you INVERT the tachion beam

[motorollin]

sir_inferno wrote:

JimS wrote:
strange... reversing the polarity always works on Star Trek.

that's cause you not only reverse the polarity, but you INVERT the tachion beam

No no no, you have to modify the deflector array to emit an inverse tachyon pulse! That will neutralise any stray chroniton particles, thus breaking the temporal causality loop. Of course, you should isolate the dilithium matrix from the EPS conduits to avoid overloading the power relays and causing a core breach.

Errr.... then your A500 will work!

--
moto

[nyteschayde]

It's been so long now that I don't quite remember but I once did a similar thing in hooking a pc power supply. I crossed the 5V and 12V lines.

I wrote the whole machine off as dead. I lost my CSA Derringer 030 and several other things. It was a sad day. I later found that by replacing all the socketed chips the machine fired right back up again.

If you manage to get a hold of some replacement chips (like Agnus, Denise, etc...) you may be able to get it up and running again. Whether it's worth it or not is up to you since it may not solve your problems.

[weirdami]

i find that reversing the polarity results in a slap in the face.

[sir_inferno]

motorollin wrote:

sir_inferno wrote:

JimS wrote:
strange... reversing the polarity always works on Star Trek.

that's cause you not only reverse the polarity, but you INVERT the tachion beam

No no no, you have to modify the deflector array to emit an inverse tachyon pulse! That will neutralise any stray chroniton particles, thus breaking the temporal causality loop.

only if you seem to be caught in a temporal wake

Of course, you should isolate the dilithium matrix from the EPS conduits to avoid overloading the power relays and causing a core breach

you know, that might just work. if we boost the dilithium matrix, we'd create a feeback loop

{insert simple analogy}

[Matt_H]

Like putting too much air in a balloon!

[Doobrey]

motorollin wrote:

No no no, you have to modify the deflector array to emit an inverse tachyon pulse! That will neutralise any stray chroniton particles, thus breaking the temporal causality loop. Of course, you should isolate the dilithium matrix from the EPS conduits to avoid overloading the power relays and causing a core breach.

Errr.... then your A500 will work!

Ah, you mean  change jumper J7 to the 2-3 position ;-)