Unknown zener - UK Vintage Radio Repair and Restoration Discussion Forum

injektilo001 · 25th Apr 2017, 4:40 am

I'm Jean Paul from Chile, new to the forum, and a begginer medium to electronics
I'm trying to repair a vintage transistor GRUNDIG all transistor Stereo RF3601
Well, the radio has no sound at all. Just a working bulb on the panel.
To make it short, i figured out on the power supply stage, a ZENER diode that is shorted, just after de bridge rectifier.
I suppose the voltage of this zener is 12V, cause on the schematics says 12V as a testing point, on each side of the zener. I had a hard time taking it out, cause the diode is screwed to a metal chasis wich act as the anode and this was soldered to the PCB. The diode says NT-9866A but i can't find any info on the net.
Another question, if this Diode is shorted, what could be the reason? and what can also be damaged if this was shorted?
I'm attaching pics of the diode and part of the schematics, sorry for the bad english
THANKS TO ALL

jonnybear · 25th Apr 2017, 5:00 pm

The AD162 may be worth checking as well for collector base short, also the feed resistor to the collector of the AD162. a 1N1353A is a 12 volt 10 watt zener if that is any help. how are you checking the zenner? I would check it with a analogue meter on ohms range.
John

Silicon · 26th Apr 2017, 12:25 pm

You can estimate the power dissipated in the zener diode by using the resistor values and voltages shown on the schematic.

The extract of the schematic is difficult to read.
One of the resistors has 21.5 Volts on one side and 12V on the other.

You can calculate the current going through it and estimate the power dissipated in the zener.

You could try a 5Watt 12V zener such as the 1N5349B.

injektilo001 · 27th Apr 2017, 12:59 pm

Hi, because of work and babies, i haven't been able to try your suggestions, but here's a link to better schematics

https://www.dropbox.com/s/w1eiah4yfh...F3601.rar?dl=0

Thanks to all

injektilo001 · 2nd May 2017, 2:34 pm

Hello.

Thanks to all for your answers.
The Grundig RF3601 is working, well, at least i can get sound of it.
The thing was this unkown zener, when I took it away, I didn't check the radio status.
But later I did, and it was working, yes, in that 12v (as the schematics says) spot where the zener goes, it reads 19v of course. But everything else works in the electronics.
Just few scratchy pots, the MONO button that doesn't stay pressed and the cord tuning system is all messed up.
One question, the place where the cord touches the tuning AXIS is just metal, and it doesn't grip at all when i turn the knob. i thing some rubber thing must be missing, cause where the cord turns and touches the axis gets thinner, and it looks like something could go around there, don't know.
any suggestions for good grip?
THANKS AGAIN

TrevorG3VLF · 3rd May 2017, 9:38 am

The thinner part of the drive shaft is so that the cord does not wind off the end. There should be about four turns around the shaft at this point. When turned the cord will wind to the side and then slip down to the centre. You obviously need some tension in the cord.

25th Apr 2017, 4:40 am	#1
injektilo001 Retired Dormant Member Join Date: Apr 2017 Location: Linares, Chile. Posts: 3	Unknown zener I'm Jean Paul from Chile, new to the forum, and a begginer medium to electronics I'm trying to repair a vintage transistor GRUNDIG all transistor Stereo RF3601 Well, the radio has no sound at all. Just a working bulb on the panel. To make it short, i figured out on the power supply stage, a ZENER diode that is shorted, just after de bridge rectifier. I suppose the voltage of this zener is 12V, cause on the schematics says 12V as a testing point, on each side of the zener. I had a hard time taking it out, cause the diode is screwed to a metal chasis wich act as the anode and this was soldered to the PCB. The diode says NT-9866A but i can't find any info on the net. Another question, if this Diode is shorted, what could be the reason? and what can also be damaged if this was shorted? I'm attaching pics of the diode and part of the schematics, sorry for the bad english THANKS TO ALL Attached Thumbnails Last edited by AC/HL; 25th Apr 2017 at 12:20 pm. Reason: Copyright material removed

25th Apr 2017, 5:00 pm	#2
jonnybear Octode Join Date: Nov 2010 Location: Cullompton, Devon, UK. Posts: 1,435	Re: Unknown zener The AD162 may be worth checking as well for collector base short, also the feed resistor to the collector of the AD162. a 1N1353A is a 12 volt 10 watt zener if that is any help. how are you checking the zenner? I would check it with a analogue meter on ohms range. John Last edited by jonnybear; 25th Apr 2017 at 5:22 pm.

26th Apr 2017, 12:25 pm	#3
Silicon Nonode Join Date: Jun 2007 Location: Coulsdon, London, UK. Posts: 2,167	Re: Unknown zener You can estimate the power dissipated in the zener diode by using the resistor values and voltages shown on the schematic. The extract of the schematic is difficult to read. One of the resistors has 21.5 Volts on one side and 12V on the other. You can calculate the current going through it and estimate the power dissipated in the zener. You could try a 5Watt 12V zener such as the 1N5349B.

27th Apr 2017, 12:59 pm	#4
injektilo001 Retired Dormant Member Join Date: Apr 2017 Location: Linares, Chile. Posts: 3	Re: Unknown zener Hi, because of work and babies, i haven't been able to try your suggestions, but here's a link to better schematics https://www.dropbox.com/s/w1eiah4yfh...F3601.rar?dl=0 Thanks to all

2nd May 2017, 2:34 pm	#5
injektilo001 Retired Dormant Member Join Date: Apr 2017 Location: Linares, Chile. Posts: 3	Re: Unknown zener Hello. Thanks to all for your answers. The Grundig RF3601 is working, well, at least i can get sound of it. The thing was this unkown zener, when I took it away, I didn't check the radio status. But later I did, and it was working, yes, in that 12v (as the schematics says) spot where the zener goes, it reads 19v of course. But everything else works in the electronics. Just few scratchy pots, the MONO button that doesn't stay pressed and the cord tuning system is all messed up. One question, the place where the cord touches the tuning AXIS is just metal, and it doesn't grip at all when i turn the knob. i thing some rubber thing must be missing, cause where the cord turns and touches the axis gets thinner, and it looks like something could go around there, don't know. any suggestions for good grip? THANKS AGAIN

3rd May 2017, 9:38 am	#6
TrevorG3VLF Rest in Peace Join Date: Apr 2011 Location: Matlock, Derbyshire, UK. Posts: 1,378	Re: Unknown zener The thinner part of the drive shaft is so that the cord does not wind off the end. There should be about four turns around the shaft at this point. When turned the cord will wind to the side and then slip down to the centre. You obviously need some tension in the cord.