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Old 21st Jun 2018, 9:44 pm   #1
GSBX1220
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Default Blaupunkt Frankfurt no FM

Hi

First post here.

I have some electronics knowledge, so hopefully with the correct guidance hopefully I can fix this

I have a Blaupunkt Frankfurt Stereo radio. I'm not sure the exact model, but it has the single row of preset buttons, and a mono/ stereo button on the upper left if the dial. I hope that helps the description, but if further info is needed, I can take some photos.

So, the issue is that it works fine on SW, MW, LW but on FM nothing. However, when tuning up the band to 108MHz I have what sounds like 2 stations together. Also, at around 104 MHz the static gets a bit louder.
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Old 21st Jun 2018, 10:05 pm   #2
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Default Re: Blaupunkt Frankfurt no FM

The first thing to try is always to clean the switchgear contacts with Servisol 10 or a similar contact cleaner. Don't use WD40 - it will clean the contacts, but also leave an oily deposit everywhere.
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Old 21st Jun 2018, 10:11 pm   #3
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Default Re: Blaupunkt Frankfurt no FM

Hi Paul

Thanks. I have done that already as the volume and tone were a bit crackly. And yes Servisol was used.
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Old 22nd Jun 2018, 11:31 am   #4
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Default Re: Blaupunkt Frankfurt no FM

Hi

If it helps, it looks as if it is this set https://www.radiomuseum.org/r/blaupu..._76384400.html
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Old 26th Jun 2018, 10:34 am   #5
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Default Re: Blaupunkt Frankfurt no FM

For further identification purposes I have attached photos of the set and the serial No. label which fell off when I took it out of the car to photograph it!

Having no FM is no real biggie at the mo as I am using my iPhone VIA the DIN plug input at the rear. However, it would be nice to have it working

I have to say, the sound from this set is quite nice. I'm outputting to a pair of JBL 4X6 speakers which are mounted very discreetly. Not much Bass, but mid & treble are nice. I'm trying not to spoil a rare 40 year old car with some sort of OTT sound system!

I do really like Blaupunkt radios. They are just right in every way. The car had a Hamburg fitted from new.
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Old 27th Jun 2018, 1:19 pm   #6
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Default Re: Blaupunkt Frankfurt no FM

In case I'm unable to find the service manual for the Frankfurt Stereo 7 638 449 010, it is available from radiomuseum.org Guests can download a limited no. of documents, or, by becoming a member, have full access to the site. Having looked at some of the diagrams, the lack of FM could, as I mentioned earlier, be in the tuner, Stereo decoder, FM I.F. or A.S.U. sections. The latter three are Hybrid Circuits, which will no longer be available, unfortunately.
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Old 29th Jun 2018, 7:44 am   #7
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Default Re: Blaupunkt Frankfurt no FM

hopefully not the hybrids. But knowing my luck it wil be!
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Old 3rd Jul 2018, 9:41 pm   #8
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Default Re: Blaupunkt Frankfurt no FM

OK

FM mysteriously started working again last night. Went back to the car today and it was not working again. Went back a bit later, it was really really hot in the garage and it was working.

Curious I started to take the radio out the car while it was playing and when doing so it started to go off tune slightly.

What I did notice was that when I squeezed the rear of the removable case bottom (middle at m5 stud area)this caused it to go off tune to the point I had no FM reception. Looking inside the only component near that area is the multi way connector which takes what I presume to be the signal from the pre amp to the power amp board. I cannot see that being the issue.

Any ideas? I think I need to go round all components in the vicinty with a soldering iron, or could it be something else?

Attached are a couple of photos of both sides of the board in that area
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Old 3rd Jul 2018, 10:46 pm   #9
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Default Re: Blaupunkt Frankfurt no FM

Hmmm. Double-sided print......could be a problem with plated-through connections....
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Old 3rd Jul 2018, 10:57 pm   #10
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Default Re: Blaupunkt Frankfurt no FM

Yes, possibly that's why I'm thinking along the lines of a possible bad connection/dry joint. And I wonder if the high temp,in my garage over the last few days has caused some slight expansion if board / joints.

Or I could be way off beam here and it could be something completely different.
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Old 4th Jul 2018, 9:20 am   #11
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Default Re: Blaupunkt Frankfurt no FM

These did sometimes suffer from poor through-print connections and dry joints. Intermittent faults in anything can be a pain to track down, but the fact that squeezing the bottom cover caused the FM to stop working points to something of that sort. Whilst those interconnecting cables rarely give trouble, they're not above suspicion, but I'd agree that re-flowing the solder joints would be the place to start.
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Old 4th Jul 2018, 10:50 am   #12
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Default Re: Blaupunkt Frankfurt no FM

Does this generation of ICE still have a trimmer screw for the aerial? Does this relate to FM or AM...or both? Not sure.

Also is the aerial properly grounded to the car chassis...corrosion?
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Old 4th Jul 2018, 1:01 pm   #13
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Default Re: Blaupunkt Frankfurt no FM

These did have an aerial Trimmer, but this is only effective on medium wave. Blaupunkt, unlike most other manufacturers, specified that the trimmer be adjusted for maximum volume on a weak signal at around 600kHz (most stated adjust for max. o/p @ 1400kHz) In any event the setting of the aerial trimmer has no effect on VHF reception.
Good point about ensuring that the aerial screening is properly earthed to the car chassis, though. In addition the Radio should be earthed via a separate ground wire, or, preferably a length of braid, unless it is securely bolted to the vehicle's metalwork. BP radios always had a 0.25" tag for the earth connection.
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Old 4th Jul 2018, 10:26 pm   #14
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Default Re: Blaupunkt Frankfurt no FM

Hi folks

I think I may have solved this.

A bit of investigation showed the most sensitive to movement part of the board was around the SN76116NB FM demodulator / PLL chip so I would suppose that movement here would account for the FM cutout & tuning drift.

A couple if vids showing this.

https://youtu.be/QrmbmEIv-F8

https://youtu.be/B0FwIy8pQEI


The soldering is indeed not that great. Looking at the board under a magnifier lamp I could see loads of pinholes in joints, incomplete joints and dry joints. I went found and re flowed them. One if the worst was the SN76116NB IC. When re doing the pins on this there was quite a bit of bubbling of the joints when touched with the iron.

This seems to have solved it. I left the unit running sitting on top of the Farnell bench supply, so combined with the heat from this & the overly hot workshop, it ran most of the afternoon and still did not cut out or drift.
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Old 5th Jul 2018, 7:59 pm   #15
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Default Re: Blaupunkt Frankfurt no FM

There is always a problem with thro' hole soldering. It ALWAYS comes back, unless you deal with it properly. It may be tomorrow, or a few years if you are lucky, but return it will.
I repaired hundreds of Grundig Tuner-IFs and self seek modules, which had many plated through holes. Mostly of course these are ground connections, but not always.
To guarantee a cure do as follows:-
Apply a HOT iron, and make it BUBBLE strongly. At some point, it will blow a bubble that bursts and leaves an opening on that side of the board. It is best if this is the component side, but not always possible. Carefully resolder the OPPOSITE side, just enough fresh solder only. Return to the "open" side, and with care and finesse, make a satisfactory bridge between the board and one side of the component. I learned to spot the dodgy boards on sight, some Telequipment scopes (D67, D67A), some Motorola car radios and the Turkish made Bush TVs with "ITT" style teletext decoders. A careful visual examination, then move in with the iron.
When I first met the Grundig CUC series Tuner-IFs, I bought a low power stereo microscope, quickly identified all the suspect joints on the many different board versions, and never looked back. Profitable repairs!
Les.
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Old 5th Jul 2018, 9:43 pm   #16
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Default Re: Blaupunkt Frankfurt no FM

In some cases it is possible to run a short length of wire through a plated hole, then re-solder both sides of the hole. I have done this on quite a few occasions on various makes of car radios & stereos
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Old 5th Jul 2018, 11:13 pm   #17
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Default Re: Blaupunkt Frankfurt no FM

Yes, some of the soldering was seriously rough in places. Also quite a lot of flux residue. Through plated can be a bit of a challenge. Back in the day when we repaired to component level, it was not uncommon for the through hole part came out with the component. This was quite common on boards that had been re worked a few times & that is where the fix mentioned by Livewire? is a lifesaver.

Talking of Telequipment scopes, I have a D61 that is dead on one channel. Been like that for years. I bought it at a radio rally many years ago and gave good service for a while. Swapped the 4mm plugs on the front for BNC's When it failed I took it into work with the intention if fixing. It came with a service manual. That was about 10 years ago and it's still there!

I'll get round to it someday. To busy fiddling with dodgy Blaupunkt stuff. Next is a Blaupunkt ACR 920 cassette player, or the Tandberg Solvsuper 10 in the loft which keeps blowing a valve in the FM stage. Cannot remember which one!
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