Newbie help diagnosing a Stereo system

Question

Hi, I have not done any of this since HS 25+ years ago, so I am a bit lost because the system is acting strange.

I have a cariole compact stereo system from the 70's recently it started having power issues. It did not always have power to the stereo part when I pushed the power button, yet the clock which is always on is still working. Now it rarely has power when pressing the power button. It has been dead for the last several months and today again I heard popping sounds coming from the speakers with the power button in the off position and found it again had power. I put on a record and played the first side, the middle of the second side the power died and its dead as a doorknob again save for the clock which is still on.

So I know it can't just be a fuse. It can't be a total power supply failure because the clock is still working. If it was a bad tube I would think it would be totally dead by now same with a bad large capacitor in the power supply. The power switch was on when it lost power, so I would assume its not the switch. The selector switch was functioning when it had power so I assume it was not that.

So where do I start in trying to diagnose this system to find out where the issue is to fix it as it works fine when it has power in the system,.

Thanks in advance.... Jim

DAB · Answer

In a system that old, you probably have some bad capacitors in the power train along with corroded contacts on switches and connectors. Time to get out a voltmeter and oscilloscope to start tracking the signal from the mains to the boards. DAB

jw0752 · Answer

Hi James,

I am very suspicious of the switch itself. These switches do wear out and certainly over twenty five years the contacts will tarnish. Once they start to arc it is the beginning of the end as the arcing produces lots of heat and makes the failure happen more quickly. The clock is probably taking power before the switch so it is not affected. If you can get it apart send some pictures of the switch. You can diagnose it quite easily by unplugging the unit and bridging the switch contacts with a jumper and then plugging it in again. Another possibility is that you have a bad solder connection on the switch. If this is the case you might be able to just resolder it. Please keep us informed of your progress.

John

jw0752 · Answer

Hi James, Sorry I can't guess more at this time. You will have to get out the tool box and crack it open and see what the situation is with the switch. By the way the link at the end of your post doesn't work for me so I can't see what you are trying to post. John

rsjsouza · Answer

napthyme wrote: What I find odd is the fact that the pops come from the speakers when the switch is set to off. I suppose its possible to arc power into the system past the switch. Its just really strange because it had not powered on a several months until today. Did you end up finding the root cause of the issue? My parents live near the ocean and over the years it is quite common to see deposits of salt on top of PCBs and switches, which would cause short circuits that could explain the pops that you are experiencing with the equipment still turned off (they had several examples of mild and catastrophic/pyrotechnic failures happening on their equipment, mainly the ones exposed to free air). Even if you do not live by the sea, all it takes is a very humid environment to allow deposits of grime to accumulate in various contacts.

dougw · Answer

We used to use TV tuner contact cleaner for intermittent connector contacts - it worked amazingly well. It seemed to exclude oxygen from the contact area.

shabaz · Answer

A few months ago I threw out some connectors, they were unused, but perhaps 15 years old (I purchased them that long ago, I know they came from a reputable source and manufacturer and not ebay - can't recall the manufacturer name now though). They were making intermittent contact, I spent days troubleshooting issues, convinced it was the software, and it turned out to be the connectors : ( Now I'm wary of using old stock connectors..

rusgray · Answer

You say that the system "rarely" has power after actuating the power switch, but you don't quantify how often it gets power. Odds are that the drive units in your speakers have a sensitivity of at least 80dB, which means that audible pops indicate a nontrivial amount of signal present at the amplifier outputs. Open the enclosure, connect the system to power through a GFCI outlet/plug, and start looking at the operation of the power supply. The potential culprits for non-deterministic operation are too numerous to list, but if you follow standard troubleshooting practices, you should be able to track the issue down quickly. If you want a quick sanity check to reassure yourself, disconnect the onboard PSU and power the electronics with a bench supply to confirm proper operation of the rest of the system (difficult loads can cause problems for some types of PSUs; this check allows you to confirm that the problem is within the PSU section.)

Newbie help diagnosing a Stereo system

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