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Old 4th Dec 2015, 11:09 pm   #61
Restoration73
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Default Re: Grundig Concert Boy 1100

Not to worry, I've got a scrap 1100 here. The transistor(s) that may have failed are
on the heatsink, (extreme right on diagram) T011,T012,T013, the first being a
circular type held in a metal C-clip, and the latter two being square and bolted direct
to the heat sink. It is most likely one of the last two has failed, but it may be a
good idea to replace both T011 is AC121 (AC128 will do) T012 is AC187K, and T013 is
AC188K. There may be something on the forum about testing these.
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Old 4th Dec 2015, 11:14 pm   #62
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Default Re: Grundig Concert Boy 1100

Quote:
Originally Posted by Restoration73 View Post
There may be something on the forum about testing these.
Here:-

https://www.vintage-radio.net/forum/...ad.php?t=42194
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Old 4th Dec 2015, 11:50 pm   #63
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Default Re: Grundig Concert Boy 1100

Thank you for the help this evening. I have found those components on the schematic. I have looked at the link about testing the transistors and I think all three need to be tested. The AC187 was red hot and the other 2 were warm. Would I need to unsolder them to test or do I test them in situ? Would it be best to replace all 3 anyway as they all got hot? But I will test them. Also is it worth replacing the C806. Can I ask what the reason would be for all 3 of these components getting hot? Is there another underlying cause?
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Old 5th Dec 2015, 1:06 am   #64
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Default Re: Grundig Concert Boy 1100

Unfortunately germaniums can sometimes fail of old age, otherwise they can be
damaged if the temperature exceeds 70 degrees. Replace all, as they are inexpensive.
Desolder them carefully and test. On the other side of the heatsink you will see
a small adjustable resistor R650 inbetween the two capacitors,it should measure 50 ohms.
Don't adjust this. C806 is unlikely to be faulty, if short circuit the fuse would have blown.
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Old 5th Dec 2015, 11:08 pm   #65
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Default Re: Grundig Concert Boy 1100

I have only managed to test the AC187K this evening so far. I have the test results from my multi-meter (I have a transistor tester on the meter but have no idea if this component is a PNP or NPN) so I have just used the resistance scale on the multi-meter (not good with multi-meters!!).
+ on C and - on E it read 930 and was still climbing,
with - on C and + on E it read 1.
Then with - to B and + to E it read 1,
- to B and + to C it read 1,
+ to B and - to C it read 163,
+ to B and - to E it read 166.
I also noticed that the pins on the transistor are very brittle, blackened and rough as if they have been red hot. Do these results mean anything to anybody? Thanks
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Old 6th Dec 2015, 12:18 am   #66
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Default Re: Grundig Concert Boy 1100

In a circuit diagram if the arrow (emitter) symbol points towards the base the transistor is a PNP. If the arrow points away from the base it's an NPN.

AC187K is an NPN
AC188K is a PNP
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Old 6th Dec 2015, 12:38 am   #67
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Default Re: Grundig Concert Boy 1100

It looks as if the meter outputs a positive voltage on the + lead so presumaply it is a digital meter. Analog meters often have the positive voltage on the black lead.

A transistor can be looked at as a couple of diodes, back to back with the base as the common connection. You have 0.163V across one and 0.166 across the other which is correct.
Put the + on the collector and the - on the emitter.
Connect a 100k resistor from collector to base and the voltage measured should drop markedly. I often use a finger as a resistance for a quick test.

The varying voltage does not look good.

Everything has to be 'upside down' for the AC188
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Old 6th Dec 2015, 1:03 am   #68
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Default Re: Grundig Concert Boy 1100

Thanks for the reply but I don't have a 100K resistor and what do you mean by using a finger as a resistance? Can I also ask what you mean by everything has to be upside down for the AC188? Looking at my schematic right at the very top left the pin configuration for T012 and T013 are identical? Sorry to ask so many daft questions but if I don't ask I don't know!
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Old 6th Dec 2015, 10:15 am   #69
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Default Re: Grundig Concert Boy 1100

I think we'd better know which service sheet you're using. I only have access to the Trader Sheet and on the circuit diagram in that sheet, TR11, 12 and 13 are at the bottom right. You'll see that there are a mixture of NPN and PNP transistors.

The pin out may be the same, but NPN types will test differently to PNP types. Don't worry about this though. So long as each junction gives a low forward volt drop one way and high resistance (1) the other, it's fine.

As for using a finger as a resistance, just touch the collector and base connections simultaneously with you finger. Wetting it may give better results.
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Old 6th Dec 2015, 11:15 am   #70
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Default Re: Grundig Concert Boy 1100

Added some clarification in blue..... HTH.

Quote:
Originally Posted by Station X View Post
The pin out may be the same, but NPN types will test differently to PNP types. Don't worry about this though. So long as each junction gives a low forward volt drop one way and high resistance (1) the other, it's fine.
Check directly collector-emitter too- this can go short leaving good e-b and c-b junctions

As for using a finger as a resistance, just touch the collector and base connections simultaneously with you finger. Wetting it may give better result.
(Whilst simultaneously monitoring the collector-emitter resistance with the meter connected the right way round for the transistor polarity)].
Digital meters on ohms have +ve on their red lead, analogue meters have -ve on the red lead (a consequence of their design).
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Old 6th Dec 2015, 11:46 am   #71
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Default Re: Grundig Concert Boy 1100

I have attached the schematic I have been looking at, pin configuration is very top left.

Last edited by poppydog; 6th Dec 2015 at 11:53 am. Reason: picture not attached
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Old 6th Dec 2015, 11:51 am   #72
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Default Re: Grundig Concert Boy 1100

There is no attachment to your post.

Whose service data are you using?

We're getting in too deep here. When it comes to TESTING transistors, so long as you can identify the base lead, the rest don't matter.
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Old 6th Dec 2015, 11:54 am   #73
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Default Re: Grundig Concert Boy 1100

It wouldn't let me send the whole schematic as it was too large a file so I have attached a snip of it
Attached Thumbnails
Click image for larger version

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Old 6th Dec 2015, 11:58 am   #74
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Default Re: Grundig Concert Boy 1100

That's way too small for me to read.

AC187K and AC188K transistors have identical pinouts. It's the internal structure that differs.
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Old 6th Dec 2015, 12:08 pm   #75
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Default Re: Grundig Concert Boy 1100

Thank you everyone, I think I will give this a miss (I was wondering when the patience would start wearing thin). I think I have gone as far as I can with this one with my very limited knowledge. I may have another look after Christmas.
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Old 6th Dec 2015, 12:13 pm   #76
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Default Re: Grundig Concert Boy 1100

You've given up far too easily. You've tested the AC187K successfully and the results look good.

Why not test the AC188K in a similar manner? Report back the results and there are any number of people on here who will advise you if the transistor is OK.
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Old 6th Dec 2015, 12:19 pm   #77
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Default Re: Grundig Concert Boy 1100

If you are a beginner, it is possible to be overwhelmed by advice given on a forum.
Why not read the very useful articles also on here;
http://www.vintage-radio.com/repair-...ion/index.html

Tony
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Old 10th Dec 2015, 10:01 pm   #78
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Default Re: Grundig Concert Boy 1100

Evening everyone, I'm afraid I am back again!! but only for 3 days while it is still strewn across the dining room table and before the decorations go up!!!!!!!

I have some tested the transistors and the results are:
AC121
+ on C and - on E = 1
- on C and + E = 1
- on B and + on C = 179
+ on B and - C = 1
+ on B and - on E = 1

AC188K
+ on C and - on E = 0 with audible alarm
- on C and + on E = 0 with audible alarm
- on B and + on C = 162
+ on B and - on C = 1
+ on B and - on E = 1

With regard to the RC650 do I need to unsolder this to test it or can I test it in situ?

Can anyone let me know where to get these resistors? or roughly what I should be paying for them? One company I have been looking at are stating that they are new but charging a fee to check that they work?
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Old 10th Dec 2015, 10:09 pm   #79
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Default Re: Grundig Concert Boy 1100

You didn't do - on B and + on E for the AC121. If you see a volt drop there the transistor is fine.

AC188K is toast.
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Old 10th Dec 2015, 10:20 pm   #80
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Default Re: Grundig Concert Boy 1100

Quote:
Originally Posted by poppydog View Post
With regard to the RC650 do I need to unsolder this to test it or can I test it in situ?
Forgive me if I'm being thick, but what's an RC650?
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