Recapping time for 128K/Plus Analog Boards

[nvdeynde]

Hi,

I have started with recapping the Analog boards of my Mac 128K to Plus series.

I have just done 2x in the last days and there were obvious differences after replacing the capacitors.
On both, the brightness pot ( the one on the Analog board to set the maximum Brightness ) was almost fully open, after replacing the caps I had to turn it almost completely closed.
The other was from a Mac 512K and had an unstable display in the first 5 minutes, like there were fast rolling barrs on the background: it's completely gone now.

The remarkable facts is that none of the Radial capacitors actually looked bad and the ESR values were still good too.
Only the plastic housing of the 4700pf filter capacitors near the AC input was cracked.
I replaced all capacitors on the analog board, except for the Ceramic one's unless their values were out of spec.

I used high-grade Panasonic or Nichicon capacitors rater 105°C and 7000 hours. These are an upgrade over the original design as this still had a lot of 85°C capacitors and definately not 7000 hours one's.

It's not cheap to do a full recap of an Analog board, as the 7000 hours are expensive, so are the filter capacitors ( there are 3x of them: 2x 4700pf, 1x 0.47uf ).
However it's something I can recommand to all fellow collectors given these board are over 25 years old.

[spiceyokooko]

Sorry to go off at a slight tangent, but given you're talking about capacitor specs it's slightly relevant.

I'm currently sourcing some replacement capacitors for my Mac II Astec power supply unit and finding it hard to find exact replacements for their physical size. I can find the correct micro farad rating (2200) and the correct voltage (25v or 35v) and the correct temperature rating (105) and a decent lifetime rating of 10,000 hours but I can't find the correct physical size (11.5mm x 37mm) the closest I can get is 12.5mm diameter x 35mm height.

How critical is that the capacitor be the same dimensions as the one it replaces? Or is it simply not that critical in terms of its performance?

This is the one Im considering - http://uk.rs-online.com/web/p/aluminium/7396831/ Handy it comes in a pack of two because I only need two!

Cheers!

[Arthegall]

I would very much appreciate any pictures you could provide. Before and after pics. Pics of the components. Pics of the soldering process.
I have several Mac Pluses that need maintenance, and the more information about how you went about doing this process, what tools you used, etc. would be helpful.

[CC_333]

...but I can't find the correct physical size (11.5mm x 37mm) the closest I can get is 12.5mm diameter x 35mm height.

I would think that it isn't a big problem IF the capacitors in question aren't crammed together (in which case bigger ones wouldn't fit as well).

c

[Trash80toHP_Mini]

The only problem I can see from a physical standpoint would be interruption of airflow. The power/cooling budget on many Macs is very tight. The numbers you quoted don't sound like a problem, given enough physical clearance for airflow.

[CC_333]

The only problem I can see from a physical standpoint would be interruption of airflow.

That's a good point. I didn't think about that.

It probably wouldn't be a problem if the machine had a fan, but with convection cooling, everything is in a certain location and is a certain size for a reason.

c

[nvdeynde]

It probably wouldn't be a problem if the machine had a fan, but with convection cooling, everything is in a certain location and is a certain size for a reason

He's talking about recapping an Astec PSU for a Mac II. I assume the Mac IIFx PSU is identical: these have a fan inside so there should be no problem.
This one is also on my To Do list...

[nvdeynde]

I would very much appreciate any pictures you could provide. Before and after pics. Pics of the components. Pics of the soldering process.

I will take some photos this weekend and post them.
There's isn't much difference between before and after: just the color of the new capacitor is sometimes different than the original one but that's about it.
I have choosen for capacitors with higher voltage so they look almost identical to the old one's.
I didn't want to go too far and cut the housing of the old capacitors and glue them on the new one's: that was a bridge too far for me.

[spiceyokooko]

He's talking about recapping an Astec PSU for a Mac II. I assume the Mac IIFx PSU is identical: these have a fan inside so there should be no problem.

I have a Mac IIfx PSU as well and they're pretty much identical on the outside, but I think they're slightly different inside, but I don't recall what that difference is.

I've taken a pic to show the capacitors I intend on replacing and they are fairly tightly grouped together.

Am I safe on getting the one I specified earlier or should I continue searching for one of the same dimensions?

Cheers!

PS Those PSU's are a right royal PITA to work on, I still haven't figured out yet how to get the whole board out!

[zuiko21]

AFAIK, the only difference between the IIfx PSU and the II/IIx is the fan speed regulation: automatically variable on the fx, while is fixed on the others. This means the IIfx PSU is somewhat quieter.

Connector etc is the same, I'm using a IIfx PSU in my IIx.

[nvdeynde]

I took some pictures of a recapped Mac Plus Analog board ( before and after ).

I mistakenly posted them in this topic:

http://68kmla.org/forums/viewtopic.php?f=7&t=18578#p176231

Sorry...

[8bitbubsy]

You did a clean and professional job there, nvdeynde! And you used high-quality capacitors too.
This is how every single retro hardware restoration should be, thumbs up!