I finally got around to tearing down the old Macintosh 512k to see what the problem is. Visually the electronics appeared fine, so it looks like I need your help, 68kMLA.
It has the documented "FLUP FLUP FLUP" noise (the floppy drive sound) when it tries to power up. It's like it's in a constant loop of powering up and powering down and the FDD spinning up over and over, creating the flup noise, confirms this theory. I heard from somewhere that this may be a fail-safe, but i'm not sure.
Larry Pina's book advised that I suspect 7 capacitors on the International logic board (C3, C24, C27, C28, C30, C31 and C32 respectively) and also turn the voltage pot down in case someone has set it too high. I have replaced those 7 capacitors and adjusted the voltage pot accordingly to no avail, the system is still Flup, Flup, Flupping away.
Next on the checklist is to visually inspect and replace the 3 rectifiers. Please also take note that the machine still appears to power cycle even with the logic board disconnected (no idea if this is normal or not) and there is no battery currently fitted in this thing.
However i'm not entirely sure I should be focusing on these rectifiers just yet. The CRT didn't need to be discharged at all, indicating not even the tube is receiving the necessary kick to turn it over. It has started a few times before to a full picture (a Sad Mac) so I know it's perfectly capable of working. Now it's not even getting a charge.
On the board are 4 200v 100uF capacitors, not documented in Larry Pina's book, which I can only assume filter the charge coming into the system from the mains. Being 200v (and AU power being 240v) makes this scenario quite likely. If the CRT isn't getting any charge, and the logic board is struggling to power up, then maybe I should instead turn my attention to these 4 capacitors next.
They aren't cheap, at around $10 a capacitor. I need 4 of them, so i'd need to sink $40 into these, otherwise i'd have bought them and tried them already.
Should I have a strong reason to suspect these 4 capacitors? If both the CRT and the logic board are struggling, then perhaps I should examine the analog board further up the line and start by removing/replacing these mains capacitors.
Does that sound logical, or am I just wasting my time?
If anyone has any further knowledge of these old systems and the Flupping issue, i'd love to hear your suggestions to get it ticking again.
Thanks
- MB
It has the documented "FLUP FLUP FLUP" noise (the floppy drive sound) when it tries to power up. It's like it's in a constant loop of powering up and powering down and the FDD spinning up over and over, creating the flup noise, confirms this theory. I heard from somewhere that this may be a fail-safe, but i'm not sure.
Larry Pina's book advised that I suspect 7 capacitors on the International logic board (C3, C24, C27, C28, C30, C31 and C32 respectively) and also turn the voltage pot down in case someone has set it too high. I have replaced those 7 capacitors and adjusted the voltage pot accordingly to no avail, the system is still Flup, Flup, Flupping away.
Next on the checklist is to visually inspect and replace the 3 rectifiers. Please also take note that the machine still appears to power cycle even with the logic board disconnected (no idea if this is normal or not) and there is no battery currently fitted in this thing.
However i'm not entirely sure I should be focusing on these rectifiers just yet. The CRT didn't need to be discharged at all, indicating not even the tube is receiving the necessary kick to turn it over. It has started a few times before to a full picture (a Sad Mac) so I know it's perfectly capable of working. Now it's not even getting a charge.
On the board are 4 200v 100uF capacitors, not documented in Larry Pina's book, which I can only assume filter the charge coming into the system from the mains. Being 200v (and AU power being 240v) makes this scenario quite likely. If the CRT isn't getting any charge, and the logic board is struggling to power up, then maybe I should instead turn my attention to these 4 capacitors next.
They aren't cheap, at around $10 a capacitor. I need 4 of them, so i'd need to sink $40 into these, otherwise i'd have bought them and tried them already.
Should I have a strong reason to suspect these 4 capacitors? If both the CRT and the logic board are struggling, then perhaps I should examine the analog board further up the line and start by removing/replacing these mains capacitors.
Does that sound logical, or am I just wasting my time?
If anyone has any further knowledge of these old systems and the Flupping issue, i'd love to hear your suggestions to get it ticking again.
Thanks
- MB