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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 7th Dec 2019, 9:36 pm   #1
Hermit6345
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Default Audio Technica AT-P120

Having just returned home after 5 months in hospital, I switched on my turntable to be met by -nothing! no leds, totally dead. I managed to download some info from anther forum and checks around the inside revealed that there is no +12 volt or +5 volt from the little heatsink mounted on its own. Removed this assembly and applied 24 volts dc to the input and both rails were good. Further checks revealed that the 12 volt rail is more or less short circuit to ground. Since the 5 volt rail is derived from the 12 volt rail, there is no 5 volt rail either.


Has anyone had any experience wth this turntable? Can replacement pcbs be obtained? Any help appreciated.



Ian
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Old 7th Dec 2019, 10:45 pm   #2
Piccy2valve
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Default Re: Audio Technica AT-P120

Hi can you post some pics and the info you found online , also a little confused by the statement

[Removed this assembly and applied 24 volts dc to the input and both rails were good. Further checks revealed that the 12 volt rail is more or less short circuit to ground.]

How can both rails be good , and then you say 12v rail is shorted and 5v rail is derived from that , unless you are saying when you connect it back in circuit the 12v rail is then pulled to ground, re the 5v rail is it a regulator fed from 12v rail that is pulling it down , if so can you isolate that and see if the 12v comes back up.

Happy to try and help with a bit more info and pics ,

Mark
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Old 8th Dec 2019, 12:48 am   #3
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Default Re: Audio Technica AT-P120

Thanks for the reply. What I did was to remove the 12/5 volt regulator p
cb and apply 24 volts to the input. Both the 12 volt and 5 volt outputs were heathy. Thus removing them from the problem. Replaced pcb and both rails at 0 volts.Now I have blown up the schematic I see a 100uF electrolytic cap as well as a 0.01 uF across the 12volt rail to ground, either might be athe culprit I suppose. The 12v rail doesn't seem to be used much.A bit cf crcuitry to do with LED driving. I have attached the schematic of the main board.
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Old 8th Dec 2019, 7:30 pm   #4
Piccy2valve
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Default Re: Audio Technica AT-P120

Hi,
Dont know what you have checked already so apologies if you have already done any of these.
1.Do you have ac volts on cn901 with it connected to pcb if not check it with it not connected.
2.With the regulator board disconnected do you have a dc voltage on pin 1 of regulator connector on main board.
If 1 = no look for a fuse on or nr transformer be Mindful of 240v on input side of tx.
If 1 = yes and 2 = no check diodes dn901 to 904 and assoc cap .
If 2 = yes then disconnect pin 4 coming from regulator board from main pcb connection does the 12v now appear if so check d905 for short , also measure 5v rail and confirm that is there if not.
Repeat the procedure with 5v rail - pin 3 on regulator connector, reconnect pin 4 - 12v rail .

See what outcomes are from above .

Last edited by Piccy2valve; 8th Dec 2019 at 7:40 pm.
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Old 9th Dec 2019, 1:02 am   #5
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Default Re: Audio Technica AT-P120

Thanks for the help. AC input seems OK, pretty near what it says on the schematic. I think that the dc voltage on the input to the regulator board is about what you would expect for the ac voltage from the transformer. What we have not done is to isolate the regulator board simply because the dc input and both 12 v and 5 v outputs are in the same connector. That was why we felt it was easier to remove the regulator board and test it on the bench psu. That tested fine. With the socket to/from the regulator board removed from the main board, a resistance measurement shows more or less a complete short circuit to ground on the 12 v pin on the main board. We need to check a couple of components on the main board (C902 and C906) apologies for geting the value of C906 wrong in my previous posting. C906 should have been 0.1uF . Thanks again for taking an interest and time to help.


Ian
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Old 9th Dec 2019, 11:21 am   #6
Piccy2valve
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Default Re: Audio Technica AT-P120

A diode or semicondutor is more likely to cause a short , check d905 / d906 , there also appears to be a voltage sensing ic which could be a culprit , just rechecked voltage sense ic is only 5v.

I cant see the motor , is that 12v ? , a 12v reg used for supplying a few leds seems a liitle overkill, to me is it a direct drive tt or belt .

Last edited by Piccy2valve; 9th Dec 2019 at 11:34 am.
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Old 14th Dec 2019, 6:44 pm   #7
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Default Re: Audio Technica AT-P120

Thanks for all the replies. Not been able to do any further checks until today. All the diodes were OK. Lifted C902, checked 12 v rail and short gone. Removed C902 and found it to be short. Replaced C902 (100uF 16vw) and turntable fully functional once more. This thread can be closed.
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