My 512k was working fine for years and then recently went to turn it on and got chime but dark screen and silence. After approximately 1 minute, smoke started rising from top vents. Powered off. Removed case and then powered back on to see where smoke was coming from. Determined it was from the C2 capacitor on the analog board. Followed steps from JDW's video on recapping an analog board. Purchased appropriate C2 replacement from Mouser (647-UHE1E472MHD6) along with a C1 capacitor replacement. It was suggested by several vintage Mac friends that I replace this one as well since they're notorious for going bad. After replacing both caps and reassembly, I powered on the machine. Got the exact same result as before the recapping: Instant chime, dark screen, silence, and then after approximately 1 minute, smoke begins rising from the new C2 cap. Video here:
C2 Capacitor Replacement on Mac 512k Analog Board Smoking
- Thread starter DarylVogel
- Start date
Hi, Daryl.
Thanks for posting the video. Smoke is evidence of a serious problem.
You have a "dead set" which is mentioned on page 109 and later in Larry Pina's book here:
If you flip through the next few pages you will note that one of the diodes it says commonly fail is CR1, and that is shown in the following schematic:
SOURCE
Note CR2 in the upper left is connected at left to L1 but at right to CR1.
Because you swapped out C2, you know it wasn't bad originally. And the fact it smokes is proof that something other than C2 is wrong in the circuit. And because only C2 is smoking, we must logically consider all components that are electrically connected to C2. And like I said, that includes the diode CR1 which is prone to failure.
I also searched through the Dead Mac Scrolls, and on page 42 it mentions machines that make the startup bong but which have a black screen:
It says to reflow solder on Pin-1 of Connector J4, and if you open the book at the URL above, it shows you where. But you need to reflow solder on ALL the connectors, actually. That's important.
If you keyword the Dead Mac Scrolls book for "smoke" you will see a lot of things that trigger smoke, but all those mentions in the book reveal something on the CRT. In your case though, you get nothing on the CRT.
Anyway, I look forward to hearing your thoughts after you've had the chance to review the aforementioned books and reflowed the solder on all connector joints.
Thanks for posting the video. Smoke is evidence of a serious problem.
You have a "dead set" which is mentioned on page 109 and later in Larry Pina's book here:
Macintosh repair & upgrade secrets : Pina, Larry : Free Download, Borrow, and Streaming : Internet Archive
xviii, 351 p. : 24 cm. +
archive.org
If you flip through the next few pages you will note that one of the diodes it says commonly fail is CR1, and that is shown in the following schematic:
SOURCE
Note CR2 in the upper left is connected at left to L1 but at right to CR1.
Because you swapped out C2, you know it wasn't bad originally. And the fact it smokes is proof that something other than C2 is wrong in the circuit. And because only C2 is smoking, we must logically consider all components that are electrically connected to C2. And like I said, that includes the diode CR1 which is prone to failure.
I also searched through the Dead Mac Scrolls, and on page 42 it mentions machines that make the startup bong but which have a black screen:
It says to reflow solder on Pin-1 of Connector J4, and if you open the book at the URL above, it shows you where. But you need to reflow solder on ALL the connectors, actually. That's important.
If you keyword the Dead Mac Scrolls book for "smoke" you will see a lot of things that trigger smoke, but all those mentions in the book reveal something on the CRT. In your case though, you get nothing on the CRT.
Anyway, I look forward to hearing your thoughts after you've had the chance to review the aforementioned books and reflowed the solder on all connector joints.
With the smoke that was coming from C2, will I need to replace that capacitor again? Just wanted to check before I order a replacement for the CR1 diode.
You haven’t measured voltage across the legs of the smoking capacitor, but you should because it must be over voltage that is causing it to smoke. If it was a matter of polarity being reversed, I would expect it to pop rather than just smoke.
Unfortunately, if the smoke is indeed coming from that capacitor, it has been compromised and would need replacing AFTER the root cause of the smoking has been found and fixed.
Unfortunately, if the smoke is indeed coming from that capacitor, it has been compromised and would need replacing AFTER the root cause of the smoking has been found and fixed.
I suggest you first check if CR1 is working properly. Touch the blue capacitor connected to the flyback 4-pin connector to see if it gets hot. Use an ammeter to measure the DC current flowing through CR1. The worst-case scenario is that the flyback connector is faulty, which will be very troublesome; I've encountered that before.
Thank you everyone for the replies and suggestions. Is there a way, perhaps using an ammeter, to *specifically* target where the issue is? I'm new to this so apologies if this is a dumb question. Having already compromised a brand new capacitor, I'm hesitant to try this/try that only to plug things in, start up the machine, and continue to compromise brand new capacitors. I realize I could just recap the entire board but I'd like to avoid that if possible.
Can we reasonably isolate the problem to ONLY items that are connected to C2? As opposed to other items not connected to C2?Hi, Daryl.
Thanks for posting the video. Smoke is evidence of a serious problem.
You have a "dead set" which is mentioned on page 109 and later in Larry Pina's book here:
Macintosh repair & upgrade secrets : Pina, Larry : Free Download, Borrow, and Streaming : Internet Archive
xviii, 351 p. : 24 cm. +archive.org
If you flip through the next few pages you will note that one of the diodes it says commonly fail is CR1, and that is shown in the following schematic:
View attachment 24335
SOURCE
Note CR2 in the upper left is connected at left to L1 but at right to CR1.
Because you swapped out C2, you know it wasn't bad originally. And the fact it smokes is proof that something other than C2 is wrong in the circuit. And because only C2 is smoking, we must logically consider all components that are electrically connected to C2. And like I said, that includes the diode CR1 which is prone to failure.
I also searched through the Dead Mac Scrolls, and on page 42 it mentions machines that make the startup bong but which have a black screen:
It says to reflow solder on Pin-1 of Connector J4, and if you open the book at the URL above, it shows you where. But you need to reflow solder on ALL the connectors, actually. That's important.
If you keyword the Dead Mac Scrolls book for "smoke" you will see a lot of things that trigger smoke, but all those mentions in the book reveal something on the CRT. In your case though, you get nothing on the CRT.
Anyway, I look forward to hearing your thoughts after you've had the chance to review the aforementioned books and reflowed the solder on all connector joints.
You determined smoke was coming from C2 and not from any other component. Therefore, C2, and everything directly connected to C2 must be examined, including solder joints and PCB traces.
The purpose of an Ammeter is to measure current, and not all Ammeters can measure high current. I have a Fluke that will only measure 60mA or so, which isn't enough headroom to troubleshoot an "excessive current" flow problem.
You must put your ammeter in series with the circuit being tested. So if you were to measure the current flowing into C2, for example, you must desolder that capacitor entirely, then run an extension wire from one leg of C2 back to the correct pad, then solder another extension leg to the other leg of C2, which in turn would be connected to your Ammeter. And finally, you would need to solder an extension wire into the open pad on the Analog Board, which in turn must connect to the other probe of your Ammeter. You then have the Ammeter in series with the capacitor to measure current flowing into it.