Macintosh Classic Project: Part 2.5

Despite being a very busy week with back-to-back projects and assignments, I couldn’t wait any longer.

Since purchasing this machine back in March, one of my biggest concerns is having to remove or repair the analog board. In compact Macs, the analog (or sweep) board is a real pain to work with. It acts as the power supply, CRT driver and also has the speaker. Therefore, it contains both line-voltage and the very high-voltage needed to drive the CRT.

Removing the analog board is a pain mostly because of the CRT. You must remove the CRT neck board (which sits on a very delicate, easy-to-break part of the CRT) and the anode cap. From there, there are some additional connectors you have to disconnect before you can remove the board from the computer.

Due to my anxiety of removing the analog board, I decided to go ahead and get it removed and over with so I can ship it off to be recapped.

Mise en place… preparing for cracking open the Mac and removing the boards. More on the tools shown later.

First, I removed the logic board and memory expansion card and placed them in separate anti-static bags. The logic board is going to make the trip along with the analog board. While the logic board has been recapped and works (to the best of my knowledge) the person doing the recapping wants to use it for testing.

Removing the logic board was the easy part. Next was to deal with the CRT and disconnecting everything… the part that has given me anxiety since the analog board died back in early June.

It wasn’t as bad as I thought. I used a flathead screwdriver connected to chassis ground via jumper wires to discharge the CRT at the anode. Since the machine has sat unplugged for several weeks now, I’m guessing there was no juice inside. (While the Classic’s analog board has a discharge resistor, you don’t want to trust it. Being shocked by a charged CRT can hurt at best, and be fatal or cause serious injury at worst. Always discharge the CRT using the proper techniques before touching the analog board or any other part of the CRT.)

Next up was the neck board, which was the part that had me really worried. The neck of the CRT is extremely fragile: I’ve heard numerous unfortunate stories where someone accidentally bonked the CRT neck and broke it. I’ve also heard where someone was too careless when removing the neck board and broke the CRT, too. Since the CRT in this machine is in pristine condition (no burn-in, bright and crisp image) I definitely don’t want to do anything that may damage it.

To deal with the hot glue holding the neck board connected to the neck of the CRT, I used some rubbing alcohol on a Q-tip to dissolve it. Then, after gently wiggling on the neck board while gently pulling, it came loose.

The neck board removed from the CRT

After that is the final connector going to the CRT – the high-voltage anode cable. This plugs into the CRT using two metal prongs that “hook” onto a connector inside. This was probably the most time-consuming and difficult part of the job, because it was being very stubborn. After about 15 minutes, it finally came loose.

A (bad) picture of the removed anode cap and where it slots into the CRT

After that, I removed the CRT ground cable (which connects at one of the corners where the CRT itself is screwed into the case) and removed the screws holding the analog board tight to the chassis. After realizing the hard drive power harness was held in with a clip on the side of the bracket, I was able to swing the analog board out and disconnect the fan cable. Then I was able to pull the entire board out.

The analog board removed. This is a revision B analog board, which has a different yoke connector than the earlier revision A board.

Just like the logic board and memory expansion daughter-card, I tried to put the analog board in an anti-static bag. But I noticed one slight issue: it wouldn’t fit. I don’t have any other anti-static bags.

I had to jury-rig a solution together. I cut two bags open and taped them together with the analog board inside. It isn’t pretty, but I’m hoping it works well enough to keep the analog board safe for the trip.

The analog board wrapped in it’s jury-rigged anti-static shell. I also found that my packaging tape has gone missing, so I had to layer regular Scotch tape on it.

I finished by setting the two analog board screws aside and installing the bucket again. Until you flip the machine around, you wouldn’t notice it’s missing the two major components that make it tick. But you can definitely feel a difference in the weight.

It looks a lot different without the logic or analog board installed.

Hopefully this brings the Classic back to life, and this time for good. The analog board will need to be recapped and cleaned, but I’m thinking a diode (specifically, diode DP6) has failed. I’ve read this is a somewhat common occurrence, and causes the issues I was having. (Bad video, hard drive wouldn’t spin up, voltage issues, etc.)

Stay tuned for part 3 – when I get the boards back and get them installed. Hopefully reassembly goes without a hitch and I can enjoy playing around with the Classic (and not the insides) again.