Vintage Blaupunkt car cassette radio problems - Page 1
Forum section: electronics / repair

author: Reesatta
author_rank: Newbie
timestamp: September 17, 2020, 02:51:56 pm
content: I've got a 1980's Blaupunkt car cassette radio (see images for model number, because I'm unsure), and both its cassette and radio functions are defect. I don't have a car to try it in because it's actually a friend's, but I've put together my own 12V power adapter, and I'm using a loose 75 Ohm FM/AM car antenna for the radio functionality. I know a thing or two about electronics, but this thing seem almost impossible to take apart (apart from the top and bottom metal pieces), which makes it hard for me to check some of the interior and its components for errors etc. I don't have a schematic or manual, and I can't find any on the internet.The problems:Radio.It seem totally dead. It should have several red lights turning on when you turn the right knob, which I guess is for AM frequency, and the two buttons below I guess controls the FM frequency. They don't light up when you turn or press any of the mentioned controls. I'm not sure about the buttons, so I've tried pressing L, M, and U (which all stay pressed) while trying to change the frequency (tell me what these mean). However, I once managed to - before I bought the antenna - get a static noise signal with a freaking small wire, which I put inside the antenna input. The red lights showed up, but I never found any radio stations, even though the lights changed as they probably should when I turned the AM knob (nothing happened when I pressed the FM buttons). I never managed to replicate this, not even with the real antenna, which is weird. Anyway, where could the error be located? What seem to be wrong with it? I tried cleaning the black stripe which the AM knob is connected to (image A3, upper left corner below the knob, also A9 zoomed in), by the way.Cassette.It should play instantly when you insert a cassette, but instead some kind of spring mechanism push it out; it doesn't stay in. A couple of times I managed to insert it and it stuck as it should, but it didn't run. Pressing both the forward and backward buttons acts as eject. The part that I've taken interest in from this mechanism can be seen in image A3 and A4 below the "black and silver wheel" in the middle, and it's the white thing. This thing is being pushed back when you insert a cassette, and the second step should be the tightening/spinning mechanism, which should rise from below (sorry, I don't know the correct terms for everything). This mechanism is triggered by the metal thingy to the left of the white thing by being pressed backwards, which I can force with a metal spudger (must be a hard object because it's quite strong). However, you must hold it in this position, because both the white and metal thing recoil. I guess both these mechanisms could be partly electrically triggered in order to work. What seem to be the problem here?Additionally, on the bottom of the unit I found some weird thing among the electrical circuits (image A5) on the circuit board between the brown wires in the lower middle. Two circuits seem to be disrupted by physical damage to the board. I'm not sure if it's intentional by design or actual damage. Anyway, I repaired these two traces with two wires (image A6). I'm not sure what this does, though. I hope I didn't do something bad. The result is still the same with both my problems and the unit doesn't seem to act any different, or shorting itself. Is this kind of disruption of a circuit common on circuit boards? At least I've never seen anything similar. Should I maybe remove my wires? By the way, the circuits above (middle top) that looks dirty are whole. I'm trying to search for irregularities with a multimeter. The few capacitors that I can see looks fine.Anyone able to help me troubleshoot this? I'd be glad to at least fix one of the problems, or maybe just discover the exact problem/s. I replaced the belt for the cassette mechanism, by the way. There are 10 attached images for analysis, named A1 to A10 for reference. I had to resize everything in order to meet the image file requirements. I've got higher resolution images, if needed. Tell me if you need an image of something specific.

author: fzabkar
author_rank: Super Contributor
timestamp: September 18, 2020, 12:45:31 am
content: Are you sure you have wired up your jig correctly? These units typically have an "always on" battery input as well as a switched 12V input via the car's accessories switch. There might also be a dimmer input for night-time lighting.

author: KE5FX
author_rank: Super Contributor
timestamp: September 18, 2020, 04:01:23 am
content: The tag that says "Montreal" is actually the model designation. Blaupunkt car radios were often named after cities.This threadsuggests that someone was able to get schematics from radiomuseum.org. Worth checking to make sure they didn't reuse the model name across different eras... it looks like they may have.I would be inclined to avoid messing with those wires and cut traces, at least until you have schematics. One of the wires looks like a gimmick capacitor, in which case it's not supposed to be connected at both ends.

author: orbanp
author_rank: Regular Contributor
timestamp: September 18, 2020, 11:01:14 pm
content: Radiomuseum indeed has the schematics of the radio:https://www.radiomuseum.org/r/blaupunkt_montreal_sm_21_7641745010.htmlYou should download it from there.Regards, Peter

author: Reesatta
author_rank: Newbie
timestamp: September 19, 2020, 04:09:20 pm
content: Thanks KE5FX and orbanp! I got some of the schematics from Radiomuseum now. Hopefully I'll understand things better by studying them.

author: Reesatta
author_rank: Newbie
timestamp: September 19, 2020, 04:25:14 pm
content: I initially read the pins from left to right +12V, -12V, +12V, and GND. I've connected two cables splitting the +12V cable from the power supply to each +12V pin, and one -12V. Grounding is connected with an ESD wrist strap to an appropriate grounded object. The Blaupunkt lights up, but I'm not so sure it operates as it should (besides from its problems) with this wiring.I've attached an image of how it should be, according to the service manual that I acquired. From what I understand, pin 1 (from left to right) is +12V, pin 2 and 3 should be bridged(?), pin 4 acts as both +12V and -12V(?) with some special module. How should I connect this with a 12V power supply with only one of each +12V and -12V? Is my initial connection setup partially right?

author: Haenk
author_rank: Super Contributor
timestamp: September 19, 2020, 09:54:13 pm
content: you will need +12V as supply and +12V as a "switched on" signal (normally from ignition, but one supply for both is good enough for testing); plus groundthe bridge is for an automated antenna (anyone remember those?), I'd say leave those pins alone