Recent content by howardc64

Just an update, Still haven't found the problem - Reflowed all the logic board recaps. - Removed the big cap just below floppy connector, cleaned up everything and resolder it - Recapped C15 since thats the messiest one due to lost pads. Made sure I got the cap onto the right trace/via points...

Should have mentioned a bit more detail - Logic board recap was over 10+ years ago with tantalums and worked fine afterwards. Had no major leaks and backup batteries didn't leak fortunately. I cleaned up residues. Did lift the pads on one of the cap for sound. Repaired it with small...

I get random freezes and errors. Sometimes doesn't boot up properly. Some times have some single pixel vertical lines when it hangs. Seems to be able to make it occur by wiggling SCSI+Floppy ribbon cables or have some shock motions (like inserting a floppy or tapping on the case) Logic+Power...

Hi, recapped the logic board and Mac works great other than date/time and PRAM doesn't survive power cycle. I have the revision 1 board (http://www.maccaps.com/MacCaps/Capacitor_Reference/Entries/1991/10/21_Macintosh_Classic_II.html) I unfortunately lifted the solders pads on the logic board...

Just following up on my successful repair of the analog board. Replaced all the brown color high temperature low ESR caps near the transformer. The screen is nice and stable afterwards but system didn't boot. Eventually got it to work so likely was just the analog board's connector to the logic...

 A bit more googling shows this group of capacitors on the power output and crowbar circuit has very high failure rate. The reason is they are close to a heat source (transformer). Mac Classic II has a fan but these capacitors are densely packed with little air flow. The capacitor furtherest...

Replacing that block of capacitors fix the problem? I just ordered all the parts. And are the 2 nearby diode usually good or bad?

Took out Analog board and look what I found! A bunch of leaky capacitors near the 12/5V power output and crowbar circuit (close to figure 15, page 22 of this doc https://68kmla.org/files/classicmac2.pdf)Hopefully replacing these will fix it. Pretty amazing the Mac still manage to boot up...

Check your ext floppy connector pin 5,6,7,8 and see if you read -12V,+5V,+12V,+12V. This probably gives pretty good indicator if logic board has all correct voltages. Page 8-9 here https://68kmla.org/files/classicmac2.pdf

Another update... Left it unplugged for 2-3 hours and plugged back in and restarted. Same pattern - no bong, dim CRT, jail bars. Checked the voltage at floppy pin 5,6,7,8. All read around 0V - after a min or so, repetitive restart+bong - after another 1/2 min or so, starts booting and no HDD...

Ok, interesting update... Powered it up again tonight to take some voltage readings off of the floppy connector (from page 8-9 of this link https://68kmla.org/files/classicmac2.pdf) .Same as yesterday, no bong sound and dark CRT with jail bars. Then while probing a pin (pin 6 I think) on the...

A little repair history - Changed out all the leaky caps on logic board 10 years ago. Replaced the battery. Everything worked great except doesn't keep date across power cycle (didn't before the repairs). Never found the problem. - Messed with it 10 months ago. A friend has better soldering...

Thanks guys. And yes, am familiarwith mouser. Previously got a contactless angle sensor there to fix my Volvo's throttle position sensor :) Did some more circuit board tracing and found what I think is the RTC (8 pin chip with small Apple logo next to the battery holder). Also found battery's...

Took apart my Classic II nearly 10 years ago for repairs. It had no sound and RTC didn't keep time across power shutdown. Back then I replaced all the chemical capacitors (a couple of lifted pads/traces with some wire repairs) along with a fresh battery. Sounds came back, but RTC still lost...

Thanks for the tip on problem isolation. Clock does work when system is powered up. Mouse Tracking speed and Speaker Volume doesn't not survive power down. I'm assuming these 2 parameters are maintained by the PRAM battery. So I guess likely somewhere between the battery and PRAM power supply...