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Old 29th Nov 2020, 12:42 pm   #1
allan
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Default Blaupunkt Car Radios

I seem to have agreed to repair some Blaupunkt car radios including Emden Frankfurt and Munster but I didn't expect to receive 27 of them, all seemingly with the same fault, as 22 are represented just by their audio input/output circuit board. This uses a pair of complementary transistors BD433/BD434.
Before studying these in detail I imagine there must be a stock fault and, as such, is likely to be known to at least one member of the forum.
Help!!!
Allan
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Old 29th Nov 2020, 1:51 pm   #2
G6ONEDave
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Default Re: Blaupunkt Car Radios

It is possible that these audio units have a stock fault of some kind but, it is also possible that they may have been damaged through supply reversal, perhaps due to a wrong connector being used to power them. The vast majority of ICE equipment that I worked on was faulty due to blown up audio stages, blown tracks and shorted components all caused by having the supply reversed. Also occassionally used to get open circuit on/off switches.
Dave
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Old 29th Nov 2020, 3:23 pm   #3
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Default Re: Blaupunkt Car Radios

I checked the two output transistors and the on/off switch Dave, at least on one of the 22 loose boards and they were OK.
I'll have to line them all up and test the other 21....
They have a mixture of small 100nF tantalums, large electrolytics and a small 22uF electrolytic but all checked OK on the sample board.
I need to look for a circuit diagram I guess
Allan
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Old 29th Nov 2020, 5:30 pm   #4
G6ONEDave
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Default Re: Blaupunkt Car Radios

Looking at the photo, and the Din socket, there could well be a control line that returns from the rest of the installation, that gives a signal to switch the amp on. A bit like some ICE units that won't work without the memory back up supply being connected to +volts. Could you post another pic showing the underside of the pcb, it might help. How many connections are in the Din socket?
Dave
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Old 29th Nov 2020, 6:22 pm   #5
orbanp1
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Default Re: Blaupunkt Car Radios

Hi Allan,

elektrotanya has a good quality service manual, if that is your radio in question (the audio output looks similar):
https://elektrotanya.com/blaupunkt_f...wnload.html#dl

From the schematics it looks like that a number of resistors are implemented by some thick- or thin-film "integrated circuit".
Remember reading about, and helping out, some other car radio (it was a German make, could have been Blaupunkt) also had similar "integrated circuit" in the audio output stage, and some of the resistors crept out of spec...

Regards, Peter
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Old 30th Nov 2020, 11:04 am   #6
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Default Re: Blaupunkt Car Radios

I found a circuit diagram for a sample of these sets that looks like it covers many of the circuit boards.
I did a first pass with magnifying goggles through them all and found most had similar problems.
The solder connections to the on/off switch on the rear of the volume control (some have a tone control pot as well) were cracked. Several, where the cracking was worst also had burnt track from the switch, including a couple with vaporised track. Also evidence that the volume control had been forced (broken rivets!) as if to stop intermittency.
I also found on others, cracked solder at some pins of the rear DIN socket.
One board was missing its volume control and that one had bad output transistors, but all the others have good output transistors.
It looks like there are two stock faults, both concerning metal fatigue (at the on/off switch due to heating effects, and the DIN socket due to vibration), both making the radio crackle or intermittently go off and on. All the on/off switches actually turn on and off but maybe they get very hot due to being under-rated and this affects their soldering? No doubt all old Blaupunkt car radios will eventually fail in this way or from a bad DIN connection?
Allan
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Old 30th Nov 2020, 12:23 pm   #7
G6ONEDave
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Default Re: Blaupunkt Car Radios

Hi Allan,
I have had a look through my collection of Blaupunkt service data and although I don't have your specific model, I do have info for the 'Hamburg' version. This has a very similat pcb to yours, the number on the pcb is '8 638 306 080'. There are 5 transistors and the rotary control is 2 gang plus switch. The output pair are BD433 and BD434. Please PM me if you would like a scanned copy of the Hamburg via email, it's not too large in size as there are only 4 pages to it.
Dave
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Old 1st Dec 2020, 2:56 pm   #8
allan
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Default Re: Blaupunkt Car Radios

That would be very useful Dave thanks.
allan at radiomuseum.co.uk will find me
I've spent another hour with a magnifying glass and meter and I think I've now found several output transistor faults. Not dead shorts though so I need to remove and test them all.
There are about half a dozen slightly different versions of the pcb but all with the same pair of BD transistors, although one is stereo.
I'm writing the exercise up to make a useful source of info.
http://www.radiomuseum.co.uk/blaupunkt.html
Presumably these radios are quite valuable?
Allan G3PIY
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