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Old 3rd Dec 2015, 10:45 pm   #41
julie_m
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Default Re: Grundig Concert Boy 1100

If the rectifier was miswired, with the - output and one of the AC inputs swapped over, it would have created a circuit from the transformer through the lamp and one of the diodes, which would have conducted on every alternate semicycle. The lamp should have protected everything, though.

Unsolder the bridge rectifier altogether. Follow the traces under the board from the transformer. Connect the two AC inputs of the bridge rectifier here. Connect the + output to the point so marked, and the - output (which, if not marked, may be assumed diagonally opposite the + output) to the remaining hole.

The plates of the original rectifier could have had any of the following combinations:
  1. 1 and 5 together = + out, 3 = - out, 2 and 4 = AC in
  2. 1 and 5 together = - out, 3 = + out, 2 and 4 = AC in
  3. 1 and 5 together and 3 = AC in, 2 = + out, 4 = - out
  4. 1 and 5 together and 3 = AC in, 2 = - out, 4 = + out
Try it again, with the lamp still in circuit, once you have rewired the rectifier correctly. If you were lucky, there will be no permanent damage.
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Old 3rd Dec 2015, 11:30 pm   #42
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Default Re: Grundig Concert Boy 1100

I have now wired everything correctly and have no bulb when switched to BATT and no bulb when on mains. When the radio is switched on the bulb is very bright. Back to square one!
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Old 4th Dec 2015, 12:04 am   #43
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Default Re: Grundig Concert Boy 1100

No, not square 1. We now know that the rectifier is OK and the short circuit is on the radio side of the switch. My first two suspects would be C805 and the output stage of the radio (not in the available circuit clip). First try removing C805. If the bulb is much dimmer and the radio hums loudly, then C805 is faulty. If the bulb stays bright and the set hums, then probably the output stage is bad.

See how it goes........
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Old 4th Dec 2015, 12:18 am   #44
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Default Re: Grundig Concert Boy 1100

Can you run it on batteries? if so does it work. Whilst running the radio off batteries or a suitable external DC source check the idle current with the volume control set to minimum. If it's below 20mA then it should be ok but if it is higher then suspect the output stage. If this radio uses a transistorised output stage rather than an IC then the idle current may start off low but rapidly rise after a few minutes this indicates that the output transistors are leaky.
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Old 4th Dec 2015, 12:24 am   #45
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Default Re: Grundig Concert Boy 1100

Thank you very much for everybody that helped tonight but my teddy and bed are awaiting, so will have another look tomorrow.
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Old 4th Dec 2015, 3:59 pm   #46
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Default Re: Grundig Concert Boy 1100

probably should have done this from the very start but I connected up a 9v dc supply switched it to batt turned the radio on and im getting a very quiet heartbeat sound through the speaker.i also cannot find a c805 on my schematic only a c806. also to use it via battery side would I need to unsolder bulb and replace with the correct fuse? thanks
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Old 4th Dec 2015, 4:10 pm   #47
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Default Re: Grundig Concert Boy 1100

C805 is shown in post 8.

If you switch to battery the bulb will be out of circuit as far as the radio's concerned, so it's immaterial whether you fit a fuse.

Heart beat sound could be a sign of a discharged or overloaded battery. What's its voltage like on load?
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Old 4th Dec 2015, 4:32 pm   #48
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Default Re: Grundig Concert Boy 1100

the voltage is very erratic unreadable. numbers on meter going up and down very quick in time to the heartbeat sound
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Old 4th Dec 2015, 4:52 pm   #49
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Default Re: Grundig Concert Boy 1100

C805 on the Trader Sheet is the electrolytic capacitor connected across the bridge rectifier downstream of the on/off switch (see the clip of the cct diagram I attached to an earlier post).

You may need to watch out for component identifying numbers. The Trader Sheets were compiled by a third party by reverse engineering and sold to general radio repair shops. The labels they assigned to various components will probably not match the component numbers on the manufacturers service sheets - these would only have been issued by the manufacturers to their own dealers' workshops.

Cheers,

Frank

NB - just noticed that C805, while it appears on the Trader cct diagram, does not appear in the component list or the location diagrams on the Traders sheets, and is probably a drafting error. From the large value, (2200uF) I'd guess that C805 is the one that appears as C806 on the component list. It lives on the main PCB among the output transistors.

Last edited by frankmcvey; 4th Dec 2015 at 5:07 pm.
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Old 4th Dec 2015, 4:57 pm   #50
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Default Re: Grundig Concert Boy 1100

Up until today, I have always seen the AC connections at opposite coners on bridge rectifiers. Today I see the AC connections adjacent to each other on a diddy bridge rectifier in a switch mode power supply.
Just to keep you on your toes.
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Old 4th Dec 2015, 5:29 pm   #51
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Default Re: Grundig Concert Boy 1100

frank mcvey on my diagram my 806 is where your 805 is. what would be the cause of my erratic meter reading whilst measuring the voltage with the radio switched on?
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Old 4th Dec 2015, 5:53 pm   #52
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Default Re: Grundig Concert Boy 1100

All the C8XX numbered capacitors are concerned with the power supply. I reckon C805 and C806 are the same cap, one of them being a misprint.

It's going to be the 2200uF cap. Just disconnect one end of it and see what happens when the radio is battery powered. It's a smoothing cap and only really used when the set is mains powered.
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Old 4th Dec 2015, 6:32 pm   #53
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Default Re: Grundig Concert Boy 1100

I've located the 2200uF cap, it's very odd looking I will try to disconnect it but it's looking like I'm going to have to disconnect the tuning cord assembly to get the plate with all the station numbers on it off. That tuning cord looks a pain.
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Old 4th Dec 2015, 7:19 pm   #54
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Default Re: Grundig Concert Boy 1100

With the back off, there are 3 screws to remove; two in the main chassis and one in the slider control bracket.

Free the tuning cap spindle from the dial drive pulley and you can ease out the chassis followed by the slider control unit. The dial drive remains in the cabinet.

Before putting it back, completely close the tuning cap and wind the tuning scale all the way down to ensure that the tuning cap agrees with the dial indication.

Best to do any fault finding and testing with batteries when the set is dismantled.

Cheers,

Frank
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Old 4th Dec 2015, 9:50 pm   #55
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Default Re: Grundig Concert Boy 1100

ive desoldered the cap the it took a lot of heat to melt the solder the cap was red hot so if it wasn't us it probably is now.fresh batteries in switched on the heartbeat sound has gone there is a very faint hiss regardless of where volume is.when switched on the battery voltage drops down to 2volt.not much progress.
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Old 4th Dec 2015, 10:01 pm   #56
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Default Re: Grundig Concert Boy 1100

If the battery is good and the voltage is dropping to 2V on load then you have a near short-circuit somewhere. Are any components getting hot?
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Old 4th Dec 2015, 10:30 pm   #57
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Default Re: Grundig Concert Boy 1100

Yes.the three that are screwed to the aluminium plate. AC187 is the only one I can read, that one is red hot and the other two beside it are warm. I can't seem to find them on the diagram
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Old 4th Dec 2015, 10:49 pm   #58
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Default Re: Grundig Concert Boy 1100

AC187 is TR12. If that's heat sinked, then TR13 AC188 will be too.

Are these three lead transistors, or is the collector connection via the can?
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Old 4th Dec 2015, 10:56 pm   #59
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Default Re: Grundig Concert Boy 1100

sorry I don't understand what you are asking!!
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Old 4th Dec 2015, 11:03 pm   #60
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Default Re: Grundig Concert Boy 1100

Transistors generally have three connections. Collector, Base and Emitter. Where they're in a can bolted to a heat sink with two bolts, the collector connection is via the can and there are only two leads.

I was going to suggest disconnecting the transistor to see whether the battery voltage rises.
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