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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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24th Apr 2017, 10:38 pm | #1 |
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Grundig Party Boy 210E
After a reverse polarity incident a while ago on my battery operated Grundig Party Boy 210E it’s been playing up ever since. A symptom included when switched on (with PP9) it was motorboating (‘farting’ noises) but if you switched it on and off a couple of times it would be ok. A few weeks later after connecting my Grundig TN4 power supply to it it hummed loudly and the output transistors gave up the ghost. These were replaced and other components were checked in the output stage. The problem I have now is if a fresh PP9 is connected or a power supply is used at 9v the radio howls, whistles and motorboats especially on LW right across the scale and a little on FM although MW seems ok, however it still picks up stations very well. What I did find was if I connected it to my bench power supply at 9v and then slowly wound it down I found that at around 8v all the noises stopped and it’s perfect. Can anybody please point me in the right direction with regards to where I should be looking? As this is one of my favourite radios and is used a lot it’s taking priority over everything else.
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24th Apr 2017, 11:06 pm | #2 |
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Re: Grundig Party Boy 210E
Are you saying it's had reverse polarity applied? If so, there will be lots of knackered electrolytics inside.
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24th Apr 2017, 11:20 pm | #3 |
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Re: Grundig Party Boy 210E
Yes Paul it has. There doesn't appear to be many electrolytics in this radio, there is a awful lot of those oblong polyprope caps though. Regards Poppydog
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24th Apr 2017, 11:30 pm | #4 |
Dekatron
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Re: Grundig Party Boy 210E
Multiple capacitor failure certainly would cause all manner of instabilities. Electrolytic capacitors can lose capacitance when reverse-biased even if they do not explode, so it might be prudent to replace them all -- but do them one at a time, testing after doing each one, to avoid introducing new faults by miswiring.
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25th Apr 2017, 8:09 am | #5 |
Hexode
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Re: Grundig Party Boy 210E
How long was the reverse polarity applied for, because if it was very brief the capacitors may have survived OK. I don't know the circuit for these, but in some radios Grundig used a zener as a shunt regulator for the RF stages, which when the supply is reversed will be a forward biased diode, thus preventing much reverse voltage appearing on that part of the circuit. The series resistor might have overheated though
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25th Apr 2017, 8:49 am | #6 |
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Re: Grundig Party Boy 210E
The reverse polarity lasted as long as it took me to pull off the battery snaps after hearing the speaker pop, however it was tried again not long after but was disconnected quickly till eventually working out what was wrong. Just one more thing, when replacing the output transistors they were drawing around 4.5 ma at idle. I didn't increase this to the 8.5ma as is specified. Apart from the noises it still sounds very good. I will look at those electrolytics tonight Regards Poppydog
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25th Apr 2017, 10:30 am | #7 |
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Re: Grundig Party Boy 210E
If the OP transistors are underbiased they will produce crossover distortion at low volume levels, but if you're happy with the sound then it won't do any harm.
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25th Apr 2017, 3:49 pm | #8 |
Heptode
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Re: Grundig Party Boy 210E
The output bias current is 5.5mA not 8.5mA at 7.5 Volts. 4.5mA will be ok but could be set to 5.5mA.
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25th Apr 2017, 10:20 pm | #9 |
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Re: Grundig Party Boy 210E
All aluminium electrolytics have been replaced (there were only 5), they were all put in my Chinese tester and according to that they were acceptable, even though one of the axial caps was starting to reveal its contents on one end (I was hoping that was the one). The radio is still making the same noises, I've obviously upset something but what and where? Before anybody says it - I haven't been twiddling . With regards to the output transistors (AC187/188) current at idle can anybody confirm what the current should be as the sheet I've got says 8.5ma at 7.5v, however its not good print so the 8 could be a 5! Not that its going to make any difference to my whistling/farting noises.
Regards Poppydog |
26th Apr 2017, 10:49 am | #10 |
Triode
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Re: Grundig Party Boy 210E
Hi, I checked the Radio and TV Servicing Book for 1971-72. the circuit diagram shows 8.5mA at 7.5V. It says to adjust R45 for 8.5mA at Link Point X.
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26th Apr 2017, 11:12 am | #11 |
Dekatron
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Re: Grundig Party Boy 210E
The Grundig service sheet also gives the output pair quiescent current as 8.5mA.
Lawrence. |
26th Apr 2017, 11:39 am | #12 |
Heptode
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Re: Grundig Party Boy 210E
Yes the MW/LW version was 5.5mA.
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26th Apr 2017, 11:57 am | #13 |
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Re: Grundig Party Boy 210E
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26th Apr 2017, 12:18 pm | #14 |
Triode
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Re: Grundig Party Boy 210E
The 210E is LW, MW and VHF.
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27th Apr 2017, 8:45 am | #15 |
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Re: Grundig Party Boy 210E
Thanks for the replies regarding the idle current, I may look to increase that this evening. Any more advice regarding the whistling and motor boating would be more than welcome. Regards Poppydog
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27th Apr 2017, 9:12 am | #16 |
Nonode
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Re: Grundig Party Boy 210E
Have you checked the electrolytic across the main supply line? This will have suffered if there has been a power supply reversal. This will give the effects that you are getting if its blown open circuit.
I had the same problem when my friend connected up his Roberts R250 to a wall wart supply that had opposite polarity. It blew out the electrolytic cap across the supply and completely spit the case of the output IC.
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27th Apr 2017, 1:42 pm | #17 |
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Re: Grundig Party Boy 210E
Quick question, are these plastic/polyester type wima caps polarized? Regards Poppydog
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27th Apr 2017, 1:47 pm | #18 |
Dekatron
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Re: Grundig Party Boy 210E
Is there supposed to be a picture?
Only electrolytic capacitors are polarized. Lawrence. Last edited by ms660; 27th Apr 2017 at 1:52 pm. |
27th Apr 2017, 2:03 pm | #19 |
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Re: Grundig Party Boy 210E
No. Sorry do you need a picture? There are loads of them in this radio. I am getting replies saying check\ change "electrolytics". there are only 5 ,which have all been changed. My schematic is showing no more polarized caps, (looking at symbols on sheet) however on the pcb I can just about see under these wimas a neg polarity sign. googling polarized polyester caps is inconclusive. Regards Poppydog
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27th Apr 2017, 2:15 pm | #20 |
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Re: Grundig Party Boy 210E
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