Macintosh Classic II Questions

[mjamesf]

So I haven't recapped the logic board yet, but I am going to recap both the analog board and the logic board quite soon. Because the CRT isn't turning on, I'm thinking it has something to do with the analog board. The hard drive does spin up, but I don't know if there is anything on it. So clearly it's powering up and it's receiving power, but there is no startup chime and no video. I also grabbed a voltmeter and measured the power through the floppy port yesterday. It is within its normal range for both the +12v and the +5v. The +12v read around 12.36v or something like that, and the +5v read at 5.00v I'm thinking the logic board is okay, but I will recap anyway. Hopefully, I can get this up and running soon.

 

[apm]

You won't see anything from the CRT without a video signal from the logic board. For that matter, the high voltage circuitry won't even power up without a horizontal sync signal from the logic board. So if +5V and +12V are fine, and there's no chime and no video, I'd say caps are by far the most likely culprit, doubly so because it is such a common fault with the Classic II.

 

[SlateBlue]

Earlier in the thread, you said the tube had a faint orange glow. What makes you certain the CRT isn't powering on? On a very basic level, if the Mac doesn't boot, nothing will be drawn on the screen. One thing at a time here... Recap the logic board first. If the problem persists, only then should you focus on the analog board. The voltages you show tell me that the analog board is ok. I don't want to sound like a jerk, but I feel like a broken record. Again, recap the logic board, then worry about the other stuff only if the new caps do not resolve the current problem.

 

[mjamesf]

Alright. Sorry for all of the confusion.

 

[SlateBlue]

No need to apologize. Just wanted to make sure you address one problem before spending time and money fixing other components that may not be broken.

 

[mjamesf]

Okay, well I happen to know someone who has experience recapping a logic board, so I'll have him do that first. If that doesn't fix the problem, then we'll troubleshoot some more. He also has experience with CRTs of all sorts and knows the components well.

 

[mjamesf]

Update: On the analog board, there were a few cracked solder joints. I had someone I knew re-flow those. Unfortunately, no progress has been made.

Still powers on with no chime and a blank screen. However, I did notice something really strange with the logic board:

Upon startup, I checked the voltages using the floppy port. They were in the correct range on the +12v, -12v, and +5v. Pretty much spot on. I check a couple minutes later with the machine still running, and the voltages had dropped significantly.

I'm guessing the logic board needs recapping, which is the next thing I want to do.

 

[Macdrone]

The logic board needed recapping first.  Those caps are always toast on the classic and II.

 

[SlateBlue]

Earlier in the thread, you said the tube had a faint orange glow. What makes you certain the CRT isn't powering on? On a very basic level, if the Mac doesn't boot, nothing will be drawn on the screen. One thing at a time here... Recap the logic board first. If the problem persists, only then should you focus on the analog board. The voltages you show tell me that the analog board is ok. I don't want to sound like a jerk, but I feel like a broken record. Again, recap the logic board, then worry about the other stuff only if the new caps do not resolve the current problem.

I said this before...

 

[aplmak]

Recap that logic board!!! And clean the logic board... I put it in the tub with 90% rubbing alcohol bath... toothbrush to get under the chips.. Use rubber gloves.. Those CAPS require replacing as everyone has mentioned.. It's the first thing I do when I get a machine.. I don't even power it on.. I do logic board then move to analog and power supply boards..

 

[mjamesf]

I'm aware the logic board needs recapping. I even stated it is the next step I'm taking.

 

[Macdrone]

We just keep saying it as no real troubleshooting can occur until that is done first.  Kind of like trying to start a car without a battery.  Nothing is going to happen  until you do that first.

 

[Mc128k]

I have a classic II that needed the recapping. It also happened that some electrolyte corroded a few VIAs and the board had to be lightly bent to make it temporarily work, so make extra attention to the damage BEFORE recapping, take some photos, these could come useful after. Also try to "divide et impera", the mac is composed of two boards, the analog and the digital. First you make sure that the power is good (measure it from the power cable with the logic board disconnected. Then you recap and try searching for issues until you hear the startup chime, and AFTER THAT you debug the screen.

And moreover, do some searches for larry pina's books. They are truly fantastic for troubleshooting.