Hello!
I'm trying to relive an old Becker car stereo from the 80s, and although I have partial success, I'm having some problems as the title says. I'll try to describe what I did until now just in case it could be useful.
When I first tried it, it wouldn't tune to any station, and both output channels gave thumping noises. While I was testing it, after some minutes it partially died (only the backlight worked). I checked the two voltage regulators and one decided to take a break. I had a spare so replaced it and it relived. Saw some whiteish corrosion under some caps in the power/regulators area so replaced them.
Having the voltage stabilization sorted, next was the FM section. Suspicious caps of the same brand and type were replaced, and now tunes and locks beautifully to stations.
Because the output was still noisy, went to the amplifier/tone control area and acted the same with the caps. And now, the left channel sounds superb, but on the right one I still have a scratchy noise.
I still didn't have time to review it, but the noise seems to be present on any source (FM/AM, have to try tape).
The noise is the same as a scratchy potentiometer would do, and is pretty loud even with volume at min. But it can't be a pot, since it does it without touching the radio (maybe stop for a few seconds and then it does it again) and because the volume and bass/treble, although you adjust them with pots, the actual tone control is done with a IC (TDA1524A).
I have the factory service manual and tomorrow I'll try to upload the schematic, but meanwhile I'd like to know your thoughts about this. I think I should review the amplifier stage. Any ideas what could generate this noise? Would a defective amplifier chip do some thing like this?
Thank you very much! (and sorry for the long text, but maybe it can help).
I'm trying to relive an old Becker car stereo from the 80s, and although I have partial success, I'm having some problems as the title says. I'll try to describe what I did until now just in case it could be useful.
When I first tried it, it wouldn't tune to any station, and both output channels gave thumping noises. While I was testing it, after some minutes it partially died (only the backlight worked). I checked the two voltage regulators and one decided to take a break. I had a spare so replaced it and it relived. Saw some whiteish corrosion under some caps in the power/regulators area so replaced them.
Having the voltage stabilization sorted, next was the FM section. Suspicious caps of the same brand and type were replaced, and now tunes and locks beautifully to stations.
Because the output was still noisy, went to the amplifier/tone control area and acted the same with the caps. And now, the left channel sounds superb, but on the right one I still have a scratchy noise.
I still didn't have time to review it, but the noise seems to be present on any source (FM/AM, have to try tape).
The noise is the same as a scratchy potentiometer would do, and is pretty loud even with volume at min. But it can't be a pot, since it does it without touching the radio (maybe stop for a few seconds and then it does it again) and because the volume and bass/treble, although you adjust them with pots, the actual tone control is done with a IC (TDA1524A).
I have the factory service manual and tomorrow I'll try to upload the schematic, but meanwhile I'd like to know your thoughts about this. I think I should review the amplifier stage. Any ideas what could generate this noise? Would a defective amplifier chip do some thing like this?
Thank you very much! (and sorry for the long text, but maybe it can help).
Spray the pots with the proper spray after washing with iso alcohol fed through a syringe to remove old dirt.
Work the pots a few times.
Long term, replacements may be needed for worn pots.
Work the pots a few times.
Long term, replacements may be needed for worn pots.
Hello! Thank you for your answer.
Maybe I'm wrong, but I don't think it could be a dirty pot problem? The pots are single track, since they are only controls for a tone IC. So if it was a dirty pot, wouldn't the problem be present on both channels? Since one channel is clear, and the other has this scratchy noise, like a bad pot or like if you were messing with a speaker connector.
By the way, the amplifier stage consists on two TDA2005 IC's, one for each channel.
Regards
Maybe I'm wrong, but I don't think it could be a dirty pot problem? The pots are single track, since they are only controls for a tone IC. So if it was a dirty pot, wouldn't the problem be present on both channels? Since one channel is clear, and the other has this scratchy noise, like a bad pot or like if you were messing with a speaker connector.
By the way, the amplifier stage consists on two TDA2005 IC's, one for each channel.
Regards
You have one tone pot for both channels, or one for each?
Spray ALL the pots and switches while you have the thing open. Tone, volume, balance, everything.
Very rarely, it is a dry joint problem, so reflow all the soldering with regular solder.
Even rarer is a faulty chip.
2005 was a single channel 5 pin IC, I know that.
Spray ALL the pots and switches while you have the thing open. Tone, volume, balance, everything.
Very rarely, it is a dry joint problem, so reflow all the soldering with regular solder.
Even rarer is a faulty chip.
2005 was a single channel 5 pin IC, I know that.
Yes, the unit has only one pot for both channels. And the noise is present without touching it.
It has one slider or two?
How can a stereo setup have only one single track tone control?
You don't have spray?
Just do it, not much chance of damage.
How can a stereo setup have only one single track tone control?
You don't have spray?
Just do it, not much chance of damage.
$4, with remote.
FM, SD Card, USB card, Bluetooth.
I replaced the tone controls as the maker had split the same channel, I reworked the circuit to use both channels, and put two channel pots for bass and treble.
Also heavier heat sink, drilled some holes in housing.
Total about $6....speakers and installation were extra.
FM, SD Card, USB card, Bluetooth.
I replaced the tone controls as the maker had split the same channel, I reworked the circuit to use both channels, and put two channel pots for bass and treble.
Also heavier heat sink, drilled some holes in housing.
Total about $6....speakers and installation were extra.
I'll try the spray.
It has only a rotary, one track potentiometer for volume. And two linear, one track potentiometers for bass and treble. But they don't control volume/bass/treble directly on the sound path, that's why they are single track. The values are adjusted through a TDA1524A Stereo tone control IC, so even if the pots were dirty, I suppose i would get volume/tone changes but not a scratchy noise.
I know about those cheap modules, but what I want is to restore the unit in its original form 🙂
Regards
Then somehow check both the chips by swapping them.
The circuit I saw had a fourth balance pot also, may be open or with resistors in a car stereo.and you will have to check the signal path.
Sometimes a leaky capacitor does that.
The circuit I saw had a fourth balance pot also, may be open or with resistors in a car stereo.and you will have to check the signal path.
Sometimes a leaky capacitor does that.
This is the schematic of the preamplifier (tone control) and output stage:
About the leaky capacitor, I ended replacing all of the electrolytics since most were leaking.
4 chips, in BTL pairs...
You need to check the connectors, spray them also.
Check the ceramic / PP caps, they go bad with age.
Or leave it on for a few days, the capacitors may reform.
You need to check the connectors, spray them also.
Check the ceramic / PP caps, they go bad with age.
Or leave it on for a few days, the capacitors may reform.
They are only two chips, represented as 4 I suppose for an easier reading of the pins (IC 501 left and IC 551 right).
https://components101.com/ics/tda2005-amplifier-pinout-datasheet
Each chip is a two channel amp, it is used here in bridged mode, the left and right (or 1 & 2) channels are used as +/- to the speaker.
My advice still applies, last chance is faulty chip. most likely bad contacts caused by age and dirt.
Each chip is a two channel amp, it is used here in bridged mode, the left and right (or 1 & 2) channels are used as +/- to the speaker.
My advice still applies, last chance is faulty chip. most likely bad contacts caused by age and dirt.
I built the stereo version using TDA2005 IC , see noise even if no input connected, noise increases if Vol is kept to max level, but when input connected the noise is reduced almost unnoticeable, I sprayed the pots and not much difference. When no input connected there is lot of noise, if I touch heatsink noise reduces a little bit. I am wondering how we can make it absolute silent when no input connected? Probably TDA7297 is better I guess.
Check heat sink to ground resistance, and also put small 4.7 or so caps on input to ground...that should work, put small pf in parallel as well.
And make sure the input continuity of RCA shielded cables is there, sometimes that is also a cause.
And make sure the input continuity of RCA shielded cables is there, sometimes that is also a cause.
