[A1200] Let's change those capacitors!

[Eclipse]

Originally Posted by rkauer

Almost right (but still wrong): 2 x 22uF 25V electrolytic non-polarized.

DOH!!
Absolutely correct. You got my point though yeah?

[Zetr0]

couldn't you just use an 22uF monolithic cap? or does it still need a radial non-polarized for the circuit?

as you know mono's have a better working life span that radial

[Shadowfire]

To elaborate on what was mentioned earlier, polarized capacitors are damaged by being installed in the wrong direction, or in an AC circuit. They aren't designed to operate in reverse polarity. Some types, as with the ones in this circuit, are damaged but the damage isn't immediately apparent. Some types present themselves as a short circuit when reversed like this. Do not ever do what Commodore did!

[rkauer]

Originally Posted by 8bitbubsy

Thanks for that site, cheap shipping!

EDIT: I can only find 16v, 35v and 50v for the 25v 22µF polarized ones. What to choose?
And the non-polarized ones are 100v

You can use the ones with bigger voltages than required, never less!

And more: bigger operational voltages on the capacitors just means it can abused more, although they are physically bigger than the designed voltage units.

[illy5603]

Like 8bitbusy, I can't find non-polarized ones that look like they will fit where they are supposed to go on the mobo.

[8bitbubsy]

Originally Posted by rkauer

You can use the ones with bigger voltages than required, never less!

And more: bigger operational voltages on the capacitors just means it can abused more, although they are physically bigger than the designed voltage units.

Ok.
But the non-polarized ones seems quite big
Should I just solder them with wires and place them somewhere, so they fit?

Originally Posted by illy5603

Like 8bitbusy, I can't find non-polarized ones that look like they will fit where they are supposed to go on the mobo.

I think you have to do as I'm going to do: Solder some wires (not kynar wires, they're too thin I think) to them, and to the solder pads... Place them somewhere they fit, but don't make the wire too long!
Maybe you can bend the cap's pins so they point to the solder pad, and solder them.. Be gentle with it lateron, such a solder method is very fragile! Wires are much better.

[Stedy]

Just ordering some capacitors myself to replace those in my A1200 and A600.

Buying mine from Rapid Electronics,http://www.rapidonline.com.

All 2000 hour life or better and the order codes are:

11-226018   	 10UF 16V 4X5.4MM 20%85C SMD ELECTROLY RC    	 £0.046  each    	   	  
11-226119 	22UF 16V 5X5.4MM 20%85C SMD ELECTROLY RC £0.058   each   			
11-226220 	47UF 16V 6.3X5.4MM 20%85C SMD ELECTRO RC £0.092  each    		
11-226321 	100UF 16V 6.3X5.4MM 20% 85C SMD ELEC RC 	£0.081 each   			
11-154622 	25V 470UF NRSZ 105DEG LONG LIFE CAP(RC) 	£0.334 each 
11-154227   	 10V 1000UF NRSZ 105DEG LONG LIFE CAP£0.288 each

I've used polarised capacitors for AC coupling circuits on video systems for many years with no problems, even when testing from -40 to +85C.

Should have these parts later this week, will let you know how I get on.

Off to check on the SMT rework station

Ian

[MagerValp]

Having recently replaced most of the SMT caps in my A4000, I recommend replacing them with regular radial lead caps, instead of SMT caps. Just bend the legs into little feet (think Motorola Invaders), and solder them to the SMT pads. You can see some examples in my A3640 thread. They are MUCH easier to solder, especially if you only have a regular soldering station.

Also, to remove the caps, I found that it works well to pinch the cap a few times with pliers, to break it inside. Then you can gently pull it up, leaving the black plastic base and the two feet still connected to the board. The black plastic is extremely brittle and can easily be picked off, leaving just the two legs exposed, which are trivial to desolder - push gently on them from the side with the tip of the hot iron and they'll just come off.

[8bitbubsy]

EDIT: Nevermind! There was two solder pads to the left of the empty FPU slot that was supposed to be shorted. I, of course, deshorted them, as I thought I shorted them on accident.


Replaced all the SMD capacitors! Checked the solder connections, the polarity, the types etc many times...
Every time I boot the miggy, I get a blinking power led (green), then it stops blinking.. I do eventually get a yellow screen! Sometimes orange and green.. even white!
It doesn't boot from floppy, hdd nor boot into "early startup screen" Don't get any pic as well!
No acc, hdd or indivision connected...

[Cosmos]

>notice that the pair very near the audio connector need to be no-polarized units instead the original (AND WRONG) polarized pair Commodore used in that place


According to the schematics (C324 & C334) => polarized !


So what ?

[Shadowfire]

Yes, the schematic shows that they are polarized.

But, you will also note, that on the (-) side near the RCA jack, they are pulled to ground by a resistor.

On the (+) side, however, you will note that it is being driven by an OPAMP whose outputs swing from +12 to -12V. When the output drops below 0V, the capacitor is actually being reversed, and this is not good for it.

[DoogUK]

I'd like to see a guide for a4000's too

[MagerValp]

Originally Posted by DoogUK

I'd like to see a guide for a4000's too

http://amiga.serveftp.net/audio_repair.html

C443 and C433 should be replaced by non-polarized caps.

[protek]

Say, has anyone used or can you use solid capacitors instead of electrolytic capacitors? It seems that some of the modern PC mobos sport the solid capacitors nowadays.

[Zetr0]

Originally Posted by protek

Say, has anyone used or can you use solid capacitors instead of electrolytic capacitors? It seems that some of the modern PC mobos sport the solid capacitors nowadays.

I think in some instances where mono's are concerned quite possibly, however I belive the disspation characteristics of the Solid Caps is slightly different than that of the radial electrolithic.

if you have a spare board, it would be interesting to experiment. Key areas would be sound and video to experiment with.

[kipper2k]

Out of all A1200/A600 boards i've looked at (and theres a lot). I have not noticed a lot of damage to the Audio caps, most of the damage being on the power related caps. I always replace them with the same type of caps., i figure they've lasted almost 20 years and still chuck out the sound that they will last another 20 years with replacements of the same type. They are just a bi of a pain to get at because of the keyboard cable header.

[Fingerlickin_B]

Ok, so just to be clear (it gets confusing when retrospective changes are made to the initial post).

The instructional picture in the very first post (as seen below in current form at time of this post) is NOW correct, yes or no?



PZ.

[8bitbubsy]

Originally Posted by Fingerlickin_B

Ok, so just to be clear (it gets confusing when retrospective changes are made to the initial post).

The instructional picture in the very first post (as seen below in current form at time of this post) is NOW correct, yes or no?



PZ.

Yep, but the topmost two cyan ones (for audio) need to be non-polarized capacitors. Except for that, it's correct yes.

[Cosmos]

I have all caps for A500/A500+/A600/A1200/A4000 for sale : 6 euros including shipping

[Fingerlickin_B]

Originally Posted by 8bitbubsy

Yep, but the topmost two cyan ones (for audio) need to be non-polarized capacitors. Except for that, it's correct yes.

Cool & many thanks (plus your picture already mentioned the non-polarised bit for audio caps anyway)

I've got the original schematic, but never acted on it...as I'd been told some faults were there...so this is great.

Thinking about Tantalum caps, but that is for another thread...see you there

PZ.