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Zetagi B300p pre amp failure
Topic Started: Monday, 5. September 2011, 12:39 (3,135 Views)
NightRunner
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26 Charlie Tango 609

My Zetagi B300p pre amp has failed, the amp still works fine ,but when i switch on the pre amp side of it i get no rx at all.
Does anyone have knowledge of these things, ie which components are likely to have failed, would appreciate some pointers as were to start as i have little knowledge of electronics and there schematics but would like to have a go at fixing it rather than binning it.
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26CT038Andy
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26 Charlie Tango 038

Hi
Ive got one with the same problem im taking it to my mates on sunday to have it repaired ill let you know when i get it back what the problem is.
Andy 26ct038
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MadMark1
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163 Charlie Tango 020
I found this schematic of a B-300-p, Although there are a few different versions of circuit board used in them, saying this though the actual way they all work is proberbly simular.

http://i925.photobucket.com/albums/ad100/madmark42/zetagib300-p.gif


From the looks of it, The switch marked Pre ( pre-amp ) switches the 12 supply to actually power the pre-amp circiut, the LED on the right of RL2 should light showing power, The coil of RL2 the is switched by the transistor BC237, This looks to be the circuit that actually work the relay to switch the pre-amp in circuit when on rx.

The actual pre-amp circuit looks to be the BC237 transistor on the far right of the schematic, I would say its proberbility this transistor at fault, If the relay is switching from tx to rx.

check to see if you have voltage on RL2, check the 1N4003 Diode next to the relay, Its across the relay coil ( to stop back Emf ) as it may be short circuit. Also check the 1N914 Diodes, just up from the antenna socket on the schematic as these can go short circuit, there there to protect the pre-amp transistor from strong signals.

Mark
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Deleted User
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The Pre-amp in my B300P is also stuffed. To be honest when it was working it was rubbish so no great loss. I have been told that 'static' can cause the pre-amp to fail. I'm not convinced though:blink:



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MadMark1
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163 Charlie Tango 020
Thats 'True' Bob, The pre-amp is poor on performance, Ok it works but as its a un-tuned circuit it will amplify everything, Including signals that arnt on your channel / frequency, This is what you hear as phantom signals or radio stations. As Bob has said its no real loss in not having the pre-amp working, But on the odd occasion it can be beneficial in having it ...


Mark
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NightRunner
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26 Charlie Tango 609

Thanks Andy i am interested to here how you get on with it,
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NightRunner
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26 Charlie Tango 609

madmark1
Monday, 5. September 2011, 15:59
I found this schematic of a B-300-p, Although there are a few different versions of circuit board used in them, saying this though the actual way they all work is proberbly simular.

http://i925.photobucket.com/albums/ad100/madmark42/zetagib300-p.gif


From the looks of it, The switch marked Pre ( pre-amp ) switches the 12 supply to actually power the pre-amp circiut, the LED on the right of RL2 should light showing power, The coil of RL2 the is switched by the transistor BC237, This looks to be the circuit that actually work the relay to switch the pre-amp in circuit when on rx.

The actual pre-amp circuit looks to be the BC237 transistor on the far right of the schematic, I would say its proberbility this transistor at fault, If the relay is switching from tx to rx.

check to see if you have voltage on RL2, check the 1N4003 Diode next to the relay, Its across the relay coil ( to stop back Emf ) as it may be short circuit. Also check the 1N914 Diodes, just up from the antenna socket on the schematic as these can go short circuit, there there to protect the pre-amp transistor from strong signals.

Mark
Thanks Mark,
I think it has gone due to a strong signal, as i was close to someone transmitting recently, so i will try and find those protection diodes you mention, although the board looks nothing like the schematic, so i go in search,
Rich
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Mark in Essex
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26 Charlie Tango 037

I also have two sets of B300P and B550P and not a single pre-amp switch working on any of them....never found it a problem as i have always found the pre amps on cheap linear's to be next to useless....will be interested to see if its an easy fix.....not that i'm going to bother doing mine ;)
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Radio Pixie
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26 Charlie Tango 052

Best thing to do with B300p preamp is disconnect it internally and replace it with a dedicated "tuned" pre-amp for 27MHz (if you can found one small enough to fit). There are often cheap pre-amps for sell on ebay. Most have gain controls, so just replace with a small pre-set resistor.
73 from Dave the Pixie 26CT052 - G7OPC - CB & Ham Radioaficionado :)

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Pigeon
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163 Charlie Tango 014

ive just had a syncron ea 300p nls can you tell me wot power i will get out of it thanks.
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