#capacitor replacement

[techav]

Repairing a Mac SE

I picked up an old Mac SE that had a bit of a problem: terrible distortion and interference appearing as horizontal lines on the monitor. It otherwise boots without issue, so the problem is most likely on the analog board.

With these old Macs, it's common to find capacitors have failed and leaked, often wreaking havoc on the boards in the process. This machine though was surprisingly clean. There were none of the telltale signs of leaked capacitor electrolyte on the top of the analog board. The connectors were all clean, with no sign of corrosion.

Removing the analog board, and the plastic insulator attached to it, did not immediately indicate the cause either. There did end up being one capacitor that had leaked through the back side of the board, but it was part of the -5V power supply, and was not involved with the video circuitry.

It took a magnifying glass and bright light at just the right angle to find the problem. There was a hairline crack in the solder around the horizontal deflection pin on the yoke connector. It was not immediately obvious, and did not appear to even follow all the way around the joint. Nevertheless, it was enough to cause problems.

I carefully reflowed the solder joints around all of the yoke connector pins and the flyback transformer, taking care to wick away much of the old solder and replace with new. Replacing the solder is a largely unnecessary step, but it ensured that the joint was well heated to prevent a cold joint, and introduced some new flux to help the solder flow properly. While I had it out, I also cleaned up and replaced the one failed capacitor on the -5V supply.

Such a tiny fix, but with a huge effect. The image is now completely stable.

This machine does need a little more work. Both of its floppy drives need cleaning and new eject gears. This unit also had been upgraded with an aftermarket internal hard drive that needs further testing. I may go ahead and replace the drive with a BlueSCSI. Finally, it only has 2.5MB of memory, so a couple new 1MB SIMMs will bring it up to a much more usable 4MB.

After that, it's time to have some fun with that PDS slot. I've got a Full Page Display video card to try out, and I'd like to try my hand at building a processor accelerator card.

Thanks to Sark and jbevren for help diagnosing the video issues on this SE.

[techav]

A Sound Repair

A couple years ago now, I cleaned up my old IIcx motherboard. It had some significant corrosion from leaking capacitors. There were a couple traces I found that had been eaten through, and in the case of R3 to C2, a via was completely gone.

I added bodge wires to fix the breaks I had found, and the machine booted and ran just fine. There was just one lingering problem — the internal speaker was mute.

The sound circuits were working. With headphones in, I could successfully test both stereo channels. But no matter what I did I couldn't get the internal speaker working.

I had hoped my bodge wires would fix it. I thought maybe it was dirty contacts inside the headphone jack. Nothing helped.

I finally sat down recently with a copy of the Bomarc schematics and found the issue.

See, unlike every other device I've encountered before, the headphone jack for the IIcx has a DPDT switch. Most devices have an SPST switch to detect when headphones are plugged in. The IIcx though uses one switch to detect when the headphones are connected, and one switch to disconnect the internal speaker.

Following the schematic, I had continuity from the speaker all the way across the motherboard (in an internal layer) to the headphone jack. On the other side of the headphone jack though, continuity was broken. What I could see of the trace was fine. My best guess is it is broken underneath the ADB filter where I can't see it.

I ran a new bodge wire — from the headphone jack to the other side of R3 — and now continuity is good all the way from the sound chip through the headphone jack, and to the internal speaker.

And now it works again.

I had missed the startup chime.

[techav]

A Quick Fix

I have a 1996 LaCie Tsunami 9GB external SCSI hard drive. It actually works just fine, but there are a couple filter capacitors on the output stage of its power supply that have leaked. I had some equivalent replacements on hand from previous repairs, so it took no time at all to replace them.

Hopefully this will keep this power supply humming along well filtered for another quarter century.

[techav]

Magic Smoke

I have a project I'm working on that needs an XT class machine, preferably at the original 4.77MHz.

I have an original IBM 5160 motherboard. It has a tantalum capacitor that is a direct short on the power supply. I also have an XT clone motherboard that I've successfully tested and booted a number of times.

I recently acquired a nearly complete XT clone system, but it was a 10MHz turbo XT, and missing its CPU. So I installed the known-good 4.77MHz XT clone board in the 10MHz clone case.

Flipped the switch and nothing happened. The power supply clicked like a switch mode supply failing to start up, so I quickly turned it back off. As the supply's capacitors slowly discharged, it continued its death click until ...

Pop goes the magic smoke.

I suspected the power supply at first. I've not had it as long, and those Rifa input filter capacitors are notorious for blowing at random times. Inside of the supply was surprisingly clean. No sign of damage, and thankfully, no sign of Rifa.

So turning attention to the motherboard, I found the culprit — a 16V tantalum filter capacitor across the 12V power supply. These too are notorious for blowing at random times.

Time for a capacitor order, I guess.

[techav]

Cleaning up a Mac Classic motherboard. This old machine was in working order when it went into storage. Unfortunately, it spent the last several years in an un-air-conditioned storage building. The case (what wasn't covered in stickers) has yellowed badly, and something was rattling inside. The plastic had gotten brittle, and the bezel cracked on the lower right corner of the screen while opening it. Turns out the rattle was from the display mount on that corner breaking sometime since it was last used. The motherboard was covered in a thick layer of dust that felt as though it had been glued on. All of the capacitors had leaked, and there is some corrosion on some surrounding chip pins. Luckily, the battery hasn't leaked, and it doesn't currently appear to have any severely damaged traces. I went ahead and pinched off the capacitor cans and cleaned up the board. I'll need to order some replacements, but wanted to get the old ones off before they caused any more damage. I am concerned about the disk drives. The floppy drive of course has a similar layer of dust inside of it that will need to be cleaned up. I should probably get some lithium grease for it. The hard drive had some oil on its sides and I'm afraid it might have leaked. The analog board still looks good. I really don't want to get into trying to replace anything on it -- a bit too far outside my skill, perhaps. Now to figure out how to remove and clean the fan ...

[harriswalter004]

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HVAC (Heating, Ventilation, and Air Conditioning) systems are essential for maintaining comfort levels in our homes or workplaces. Within these systems, capacitors play a crucial role in regulating electrical currents and providing the necessary power for various components to function effectively.

[harriswalter004]

How often should the HVAC system's capacitor be replaced?

HVAC (Heating, Ventilation, and Air Conditioning) systems are essential for maintaining comfort levels in our homes or workplaces. Within th

[harriswalter004]

How often should the HVAC system's capacitor be replaced?

HVAC (Heating, Ventilation, and Air Conditioning) systems are essential for maintaining comfort levels in our homes or workplaces. Within th