Hi!
I'm trying to repair an old car stereo which have some odd problems, I'm commenting it on the car audio subforum.
But there is a strange problem that probably belongs here better, and I hope you could help me, because although I have not problems with troubleshooting and repairing electronics, I don't have much idea about radios, and changing parts without knowing its not the best solution... if not making it worse.
The problem I refer to is as follows:
-at first, when using the search function, it doesn't detect or lock to any station. Manually searching for stations doesn't seems to get anything. You could hear the typical noise of not getting any station.
-as the time passes, without touching the search button, and the LCD displaying a fixed MHz value, you could start to hear a station. It becomes clearer and clearer and then fades away... then another station appears, the fade away.... and so on. With time it gets stronger reception and even the stereo signal lights on, but it won't lock. It keeps like tuning forever, any station, but without changing the band displayed. At this time the search function sometimes stops on some stations, sometimes not, but although it stops, you can hear the radio constantly and slowly tuning. It seems to get better and better with time but didn't want to run it much time risking to burn anything.
The radio uses some TDA's for FM tuning and PLL-synth. Because of the "getting better" situation I was hoping for capacitors, but I'm not too sure with this. If I left it unplugged for a few days, you are back to hearing nothing until some time powered on.
Have anyone heard of something like this before? Could be something apart from caps? It has some golden FRAKOS and blue axial Philips caps that I think are worth replacing.
Thank you very much
I'm trying to repair an old car stereo which have some odd problems, I'm commenting it on the car audio subforum.
But there is a strange problem that probably belongs here better, and I hope you could help me, because although I have not problems with troubleshooting and repairing electronics, I don't have much idea about radios, and changing parts without knowing its not the best solution... if not making it worse.
The problem I refer to is as follows:
-at first, when using the search function, it doesn't detect or lock to any station. Manually searching for stations doesn't seems to get anything. You could hear the typical noise of not getting any station.
-as the time passes, without touching the search button, and the LCD displaying a fixed MHz value, you could start to hear a station. It becomes clearer and clearer and then fades away... then another station appears, the fade away.... and so on. With time it gets stronger reception and even the stereo signal lights on, but it won't lock. It keeps like tuning forever, any station, but without changing the band displayed. At this time the search function sometimes stops on some stations, sometimes not, but although it stops, you can hear the radio constantly and slowly tuning. It seems to get better and better with time but didn't want to run it much time risking to burn anything.
The radio uses some TDA's for FM tuning and PLL-synth. Because of the "getting better" situation I was hoping for capacitors, but I'm not too sure with this. If I left it unplugged for a few days, you are back to hearing nothing until some time powered on.
Have anyone heard of something like this before? Could be something apart from caps? It has some golden FRAKOS and blue axial Philips caps that I think are worth replacing.
Thank you very much
Could be a problem in the PSU for the tuning voltage. Philips blue electrolytics are generally reliable but one may have gone leaky or low in value.
Or could be a problem in the received signal strength (RSS) circuit, which may be used to stop the frequency scan.
The fact that it seems to improve with use, then gets worse when unused, is consistent with an old electrolytic which is partially re-forming but not enough to function properly.
Or could be a problem in the received signal strength (RSS) circuit, which may be used to stop the frequency scan.
The fact that it seems to improve with use, then gets worse when unused, is consistent with an old electrolytic which is partially re-forming but not enough to function properly.
Sorry, I was not sure about where to put this thread 
Today I ordered a large list of capacitors (all Rubycon and Panasonic FR/FM) and one Multicomp as they didn't had it without buying a large amount of them (22uF 10V).
When they arrive I'll have to put the soldering iron and desolder pump to work. I'm not going to get bored (or yes): they are a total of 45 only electrolytic capacitors.
For the moment the MKT's and tantalums are staying (I think they are not so prone to fail).
I will inform with the results
Today I ordered a large list of capacitors (all Rubycon and Panasonic FR/FM) and one Multicomp as they didn't had it without buying a large amount of them (22uF 10V).
When they arrive I'll have to put the soldering iron and desolder pump to work. I'm not going to get bored (or yes): they are a total of 45 only electrolytic capacitors.
For the moment the MKT's and tantalums are staying (I think they are not so prone to fail).
I will inform with the results
As far as I understand, the proper procedure for working on defective Electronics is to FIRST repair the unit down to the defective component level.
Once the unit is working correctly, selection of different Color capacitors can commence, one part at a time, listening to possible improvements in the Sound.
This kind of fooling around results in a dead piece of gear or even poorer performance.
Once the unit is working correctly, selection of different Color capacitors can commence, one part at a time, listening to possible improvements in the Sound.
This kind of fooling around results in a dead piece of gear or even poorer performance.
An old harman kardon / becker technician told me that on these old equipment you should first replace all the electrolytics due to the risk of them shorting or bleeding, especially the FRAKOS. And then, if the problem is not resolved, search for other causes.
Actually, I read your opinion and the technician one on various sites, so it seems there is no agreement on what to do on this cases
Actually, I read your opinion and the technician one on various sites, so it seems there is no agreement on what to do on this cases
I am firmly of the opinion that old electronics should be repaired first, then (maybe) future-proofed. Changing all the electrolytics is a quick way to stop it working altogether. It avoids the need for thinking; some repair technicians may welcome this.
Change the caps which look or measure defective. Then analyse what is happening, when and why, to narrow down the likely faulty components. Start changing these one at a time. Really old equipment may have several faults.
Don't be tempted to 'improve' it by using 'audiophile' components. If it sounds bad after full repair then this means the circuit is poor.
Change the caps which look or measure defective. Then analyse what is happening, when and why, to narrow down the likely faulty components. Start changing these one at a time. Really old equipment may have several faults.
Don't be tempted to 'improve' it by using 'audiophile' components. If it sounds bad after full repair then this means the circuit is poor.
I'm not using audiophile caps, just good caps from known manufacturers. I have to change the final amp caps because when you turn the radio on after a long period disconnected, you can only hear hissing and the volume can't be regulated with the volume encoder. The encoder just start woring after 10 minutes or so and the hissing dissapears.
The problem is, I don't have a cap tester, so I suppose the only thing I can do is desolder each one and measure if it's not shorted? But I can't measure capacitance leakage.
Traditional radio service technicians could not measure cap value, so they usually checked for shorts with a normal meter. If OK they then temporarily paralleled the cap with another; if this fixed the fault then they replaced the cap. Cap leakage can often be determined by using a meter and Ohm's law to see how circuit voltages vary from what they should be.
Many radio faults can be found by using a voltmeter.
Many radio faults can be found by using a voltmeter.
Ok, so I proceeded extract some electrolytics from the path between transistors and amplifiers, and they were shorted. Same thing with the FM IC ones, so proceeded to change them.
Changed the electrolytics on the path from the transistors to the final amps. Now volume is regulable BUT there is a low pitched hum that I dont remember before. Maybe it could be AC coupling from the speaker wires being close to the supply but I have to test in car... Not sure if it only happens in FM.
About the FM, changed the electrolytics around the FM IC and now it locks to the stations ☺ the only FM thing that doesnt works is the auto tune becaie of a electrolytic I didnt have to replace.
AM still doesnt works, and being all the electrolytics from the same manufacturer looks like Isabel have some work...
Any ideas for the humming?
thank you ☺
Changed the electrolytics on the path from the transistors to the final amps. Now volume is regulable BUT there is a low pitched hum that I dont remember before. Maybe it could be AC coupling from the speaker wires being close to the supply but I have to test in car... Not sure if it only happens in FM.
About the FM, changed the electrolytics around the FM IC and now it locks to the stations ☺ the only FM thing that doesnt works is the auto tune becaie of a electrolytic I didnt have to replace.
AM still doesnt works, and being all the electrolytics from the same manufacturer looks like Isabel have some work...
Any ideas for the humming?
thank you ☺
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