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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 15th Oct 2018, 3:39 pm   #1
NorfolkDaveUK
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Default Pye 9123 no record

Hi guys ,
I`m trying to diagnose no record on this deck , there is no schematic (that I can find ) for this deck so I`m using the 4308 Philips schematic , this unit is a clone of that so it should be usable , BUT , every thing seems to be backwards . For instance , in the pic you can see the orientation of those caps , the negative is toward the out side of the board , in the actual 9123 unit they are the other way around the positive is out . I have re-capped it but I`m always uber careful about these things (and the unit is working find apart from record) . Has anyone worked on one of these before ? Anyone have the schematic for it ?

I`m kinda in the dark without it . My skill level isn`t good enough to work it out it seems . I still get a bit lost when it comes to diagnosing no record , people tell me to "check for bias " and I really don`t understand what that means so some proper guidance there (including telling me what bias actually is ) would be of great benefit .

Many thanks as always

David
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Old 15th Oct 2018, 3:49 pm   #2
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Default Re: pye 9123 no record

The black line towards the end of the capacitors in your diagram will be the rolled indent that's towards the +ve end of the capacitor that forms the stop for the end cap..

Lawrence.
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Old 15th Oct 2018, 4:01 pm   #3
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Default Re: pye 9123 no record

Ahh ok thanks Lawrence . That makes a lot more sense . Would make a lot more sense if they used a + like they do in most .The black line on a cap is negative .... Thanks Philips ...again ..lol .

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Old 15th Oct 2018, 4:52 pm   #4
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Default Re: pye 9123 no record

Bias needs to applied during recording otherwise the recording when played back will be distorted, in effect, the bias shifts the recording signal (which rides on the bias) up to the correct point on the linear part of the transfer curve, the frequency of the bias signal used is high compared to the audio frequency, that means it can also be used to erase the tape prior to the magnetic recording taking place, it's the function of the bias oscillator to supply the bias for the tape, usually via the record head, and also to supply the erase head, have a quick look at this, the first few drawings cover the basics for tape bias (better descriptions might be available):

http://hccc.org.uk/acbias.html

Lawrence.
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Old 15th Oct 2018, 5:40 pm   #5
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Default Re: pye 9123 no record

OK I`ve now got erase back , the inductor T3 was broken , lost a little bit of wire off it but its still allowing the head to erase so all good . Now I just need to figure out why the signal isnt getting to the record head on indeed if the record head is any good .

How can I check these combined heads for dead record sides ?

Thank you Lawrence , we were typing at the same time sorry about that .

I`ll have a read now thank you .
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Old 15th Oct 2018, 6:25 pm   #6
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Default Re: pye 9123 no record

The playback head is the same as the record head on these basic machines. Therefore if there is playback that head is good.
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Old 15th Oct 2018, 7:30 pm   #7
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Default Re: pye 9123 no record

Excellent thanks . the playback is brill , im always surprised how good these sound .

im trying to trace the signal but the schematic is not your usual layout , but the it is a Philips i guess ..lol
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Old 15th Oct 2018, 7:50 pm   #8
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Default Re: pye 9123 no record

Which input are you using, radio/phono or mic?

Lawrence.
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Old 15th Oct 2018, 9:04 pm   #9
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Default Re: Pye 9123 no record

radio/phono bud , using stereo as the output .
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Old 15th Oct 2018, 9:28 pm   #10
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Default Re: Pye 9123 no record

Quote:
Originally Posted by NorfolkDaveUK View Post
...., using stereo as the output ...
The Stereo socket on these machines is wired for connection to an additional preamplifier and not really as an output socket in its own right.

A line level signal should be present on pins 3 and 5 with pin 2 as ground/earth of the Radio/Phono socket.

Regards

Andrew
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Old 15th Oct 2018, 10:15 pm   #11
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Default Re: Pye 9123 no record

Hi Andrew , thanks for that . I`ve got the output no problem . The stereo output is going into my amp and giving me a good sound out . The issue I`m having is the deck isn`t recording .

Thanks mate .
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Old 15th Oct 2018, 10:49 pm   #12
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Default Re: Pye 9123 no record

Ahh just found a much better manual ....
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Old 16th Oct 2018, 9:03 am   #13
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Default Re: Pye 9123 no record

You have to be very careful dismantling these units as the oscillator coils are on an exposed piece of circuit board. If you knock the case into this during removal a new coil will be needed.
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Old 16th Oct 2018, 10:05 am   #14
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Default Re: Pye 9123 no record

Does the record level meter indicate ok when recording?

Lawrence.
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Old 16th Oct 2018, 10:44 am   #15
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Default Re: Pye 9123 no record

Yes bud , the level meter is working fine , erase is working fine , just no signal going to the tape . I`ve been testing voltages and the voltage at t10 is high . It should be c10 b0.1 e0.78 and its c12 b1.5 e1.5 when on record all 0`s at playback though . L1 coil was broken , I repaired that and erase is now working and its still measuring 34 ohms , it should measure 32 but I dont think thats going to make much of a difference but that probably explains the high voltage, its still erasing . I`m working with a horrible board here , the PO has "had a go" , theres a lot of repaired traces and a LOT of the solder mask is missing so I`m trying to methodically go through and look for shorts but its not easy ..lol
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Old 16th Oct 2018, 11:18 am   #16
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Default Re: Pye 9123 no record

If it's not something simple like switch contacts, wire off, poor connection etc I would 'scope the signal path, so far everything suggests that the amplifier stages are working ok as is the bias oscillator.

Lawrence.
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Old 16th Oct 2018, 11:26 am   #17
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Default Re: Pye 9123 no record

Yeah I`m trying to do that Lawrence but I`m finding it really difficult to see the path though the schematic , I can normally do it ok but this schematic is a philips and you know how they like to be different ..lol . I`ll try and draw the path onto the schematic and see if I can trace it . Thanks for your help
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Old 16th Oct 2018, 11:34 am   #18
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Default Re: Pye 9123 no record

Both sides of R565 would be a good place to check with the 'scope when recording, feed a 1kHz signal at approx. 90mV (RMS) to the phono input for the signal source.

Lawrence.
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Old 16th Oct 2018, 11:44 am   #19
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Default Re: Pye 9123 no record

Thanks i`ll give that a go !
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Old 16th Oct 2018, 11:50 am   #20
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Default Re: Pye 9123 no record

Just to note, use pin 3 of Skt1 for the input.

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