1966 Airline am/fm/phono with overheating filter caps
 

Hi all, I am having a problem with an Airline model GHJ2346A overheating the filter capacitors. The schematic I have to work with is Sams Set 892 Folder 4. I found nearly all the electrolytic capacitors had failed in some way. Either open, high esr, or the capacitance value had drifted out of tolerance. Here is the work I've done so far. I replaced the multi-section 1000/500mfd @35 volt with a 1000mfd@63v, and a 470mfd@63v. On the original can X is 500mfd, Y is common, and Z 1000mfd, and I double checked the replacements with a dmm, and esr meter, also checked polarity before soldering in place. I went through each module the same way one at a time checking each capacitor as mentioned above before soldering in place. I also powered up the unit after replacing two or three capacitors to check for improvement of operation, or for disaster. Thankfully I got improvement in performance upon each power up. After replacing all electrolytics I did a final smoke test. While the performance greatly improved, I noticed the filter cap tops swelling, were quite warm to the touch, along with a tiny bit of electrolyte boiling out the vent seam, so quickly shut it down. I can operate it for a few minutes at a time to check some voltages with higher voltage rated caps installed, but they still get very warm after 5 minutes of operation. So far I have checked voltages at the six transistors on the power supply board:
Sams voltage| Actual voltage
Q15: E 0, B -.1, C -10.5 | E -.004, B -.1, C -9.8
Q19: E 0, B -.1, C -10.5 | E -.0046, B -.00016, C -10.6
Q14: E -10.5, B -10.6, C -17| E -9.84, B -10.02, C -20
Q18: E -10.5, B -10.6, C -17| E -10.4, B -10.6, C -20
Q17: E -16, B -15.4, C-.6 | E -15, B -14.5, C -.4
Q13: E -16, B -15.4, C-.6 | E -14.70, B -13.90, C -.7
Do these voltages seem within acceptable range? Something I'm overlooking? I'm getting am, and fm reception loud, and clear throughout the dial range. Any help to steer me in the right direction to resolve the overheating capacitors is much appreciated!

One thing to check--Make SURE--you have the caps wired right. I say this because a LOT of vintage SS stereo and amps which use PNP transistor topology, had POSITIVE ground--NOT negative. I would say a 66 model would fall into this category.


If this is not the problem...there may be some sort of "spike" getting to the caps. Perhaps a bit too much AC ripple getting to them. Leaky B+ diodes WILL cause this . After all--you have plenty of voltage margin on the caps--so it HAS to be something like that.

Thank you!!! Polarity is exactly what the problem was. I was thinking about the problem while I had the can in my hand, checking it once again and sure enough there is was, " Y common positive." One of those duh moments for sure, but she's running great now! Ran about 30 minutes with no problems. Now to tackle the turntable.

Glad you got it fixed. That is one thing to remember on old solid state amps--watch ground polarity. On newer SS and tube gear---ground is nearly always negative--but NOT on germanium gear--as found from about 1963-1970 or so.