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Classic II - chimes and boots normally, but no CRT image

Byrd

Well-known member
Hi all,

I've been restoring a Mac Classic II for some time, it came to me in fair shape with the logic board being the best looking part of the lot - turned on to a "flup, flup, flup" sound and nothing else.

So far I've:

- Recapped motherboard (a pleasant job - it wasn't that degraded)

- Recapped analog board (the caps on the analog board were badly leaking - probably the worst I've seen but cleaned up well with no apparent trace damage), reflowed what I could

... the above resulted in the same "flup flup flup" sound as before, +5 and +12V voltages very low

Next steps, thanks to reading these forums ...

- Replaced zener diodes DP5 and DP7 with same (the old diodes checked out OK)

- Replaced CNY75GB optocoupler with same (TDA4605 is on the way)

... this resulted in a loud clear chime, solid +5V ~ 5.00V and +12V ~ 11.8V voltages

... I can boot from floppy or a floppy Emu assume to desktop

However, no CRT activity whatsoever (I've tried to adjust brightness on the back pot, reflowed analog and neck board).  The back of the neck is glowing orange and I'm a tad stumped.  Short of waiting for that TDA4605, would others have any further pointers?

Thank you

JB

 
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SuperSVGA

Well-known member
The orange glow means the heater is probably getting voltage fine, but you aren't getting an image. So at least that part of the video/neck board is working.

Unless the logic board isn't outputting video for some reason, I would say the problem is in the analog board somewhere. I'm not sure if the heater voltage comes from the flyback or the main power supply on the Classic II.

I doubt anything is wrong on the yoke, or else you should have at least had something on the display.

Other than that you might need to go over the board some more and double check there aren't any cracked solder joints or bad resistors, etc.

 

Byrd

Well-known member
Hi SuperSVGA,

thanks for the help - good to know if I'm getting CRT "activity" on the neck board that part is OK.  Looks like I'm down the route of checking for resistors on the analog board now, which I must admit while clean there is high chance of one or two resistors being taken out by corrosion.

JB

 

Plasticoat

Member
Did anybody come up with the solution to this problem?

I have exactly the same symptoms, I’ll resolder

some joints today.

the board has been totally recapped, so I’m hoping that should do it.

 

Plasticoat

Member
Ok, so I re soldered the joints on the usual suspects, and reflowed on some others, 

restarted and I have an image.

it’s very dark, and only 50/50 , the board powers a hard disk and floppy drive, but they do not allow a boot process to start

9CD7C14A-5C93-409E-BD6F-B7FDF61C1A49.jpeg

 
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Plasticoat

Member
Hi all, just wanted to say “Thanks” to all

i have success  

let the clean up begin.....

btw, for future reference, its a revision b classic

B40EBA66-867B-4468-BA61-A7F67E1EFC82.jpeg

 
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Byrd

Well-known member
This Classic II I'm repairing will always make me think of a certain pandemic - got it March 2020, still working on it :D

I ended up sourcing a (dead but clean) Classic I analog board, which has a different CRT yoke connector (using a compatible Apple IIc 9" CRT), given a complete overhaul having replaced the zener diodes, TDA4605, CNY17B optocoupler, vregs, all caps. The result = very marginal +4V rail and +10V fully adjusted (PP1 voltage adjustment maxed), no motherboard chime. I'd say nothing else I can do here.

So I've gone back to the original CRT, and Classic II analog board. Using the Classic I analog board as reference, I methodically cleaned up everything again, desoldered and checked caps, replaced vregs. The result = same as before, strong loud motherboard chime, rock solid +5V and +12V rails, it boots to desktop (HD, floppy or floppy emu), CRT heater is on, but no CRT activity whatsoever. I reflowed, fluxed and cleaned anything that looked remotely cruddy on the motherboard. ROM chips cleaned and reseated as well.

Next up, I'll try another CRT from my junker SE/30 - the Classic CRT doesn't look bad but need to rule it out.

What next would you kind members suggest? :)

Thanks

JB
 

LaPorta

Well-known member
Good grief, man...what a challenge. Have you possibly put a scope on the actual video signal pin coming from the logic board and seeing if there is a signal coming from it? Verifying if there is an actual video signal would be one thing to rule out.
 

Byrd

Well-known member
I was waiting for someone to say get a scope :) Argh, I was hoping to avoid one, never been there - would you have a recommendation on a cheap scope that'd just do the job?
 

LaPorta

Well-known member
I’m by no means anything but an absolute scope novice. I’ve used it maybe 10 times ever to help diagnose something (though I’d like to get better). It did help me troubleshoot a few things though. Looking for the mere presence of a signal vs none.
 

joshc

Well-known member
Further proof, that we didn't need, because we know it already, that these boards are just the worst !!

Good luck with it, I hope you find a way of getting it working. You seem to have followed all the right steps.
 
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