I`ve been trying to get this amp running properly now for long time and it now seems that a previous repair was not done correctly, the zener diodes near the input that are Adcom specials, (look like transistor), may been replaced with the wrong value, the zener diodes left channel are d111,d112,d113 and d114, the right channel are d161,d162,163 and 164.
Does anyone know or can measure the correct voltage of these zener diodes for me so i can finally get this amp up and running properly.
Cheers, manly thanks from downunder in Australia, George.
Does anyone know or can measure the correct voltage of these zener diodes for me so i can finally get this amp up and running properly.
Cheers, manly thanks from downunder in Australia, George.
georgehifi said:
Are you shure that they are zeners and not transistors???....is not usual so much zeners at the input of a amplifier...
As they are 4 for each channel it seems that they are a double diferencial (double LTP)...😉
Oh, yeah their zeners alright, not right at the input but close, i`ve got the circuit, if only i knew how to post the circuit diagram i`d put it on one of these posts so you guys could see it, is it easy as i`m hopless on a computer. (Yeah they look like transistors three legs but two are linked together on the board.)
They might be zeners...with those transistor packaging...commonly known as voltage references...but I'm not sure if they are used in amps...
Nuh, Ben, good try but the gfa-555 is a different circuit to the 585, can anyone tell me in simple english how to post the circuit i have for the 585 it might help to get to the value of the zener diodes.
Cheers
Cheers
Hi George,
U can try scan the schematic with a scanner with a PC attached
or use a digital camera to take several portion.
Thanks
U can try scan the schematic with a scanner with a PC attached
or use a digital camera to take several portion.
Thanks
Yep, very close, what model is that? it`s almost the same, the zener diodes are the ones in the bottom left corner.
Can anyone now let my know what voltage zeners they are?
Cheers George. Thanks DJK!
Can anyone now let my know what voltage zeners they are?
Cheers George. Thanks DJK!
Hi George,
They are zener diode in series to clamp down the supply voltage
to approx. 12 - 18 v for the servo amp. You can series two 6.8v
or 7.5v zener to get a voltage of 13 or 15v to supply the servo
IC.
They are zener diode in series to clamp down the supply voltage
to approx. 12 - 18 v for the servo amp. You can series two 6.8v
or 7.5v zener to get a voltage of 13 or 15v to supply the servo
IC.
Thanks Ben, you da man, i can get 15v 5watt zeners at the local corner shop for a dollar each, so one of those across each capacitor should do the trick, am i right, thanks.
Transistor/zeners
Possibly these are in fact transistors wired as zeners.
If you connect collector and emitter and apply a negative voltage (for a NPN) to the base, the device will act as a zener diode with a voltage appr. 5-8 Volts.
Regards
Arne
Possibly these are in fact transistors wired as zeners.
If you connect collector and emitter and apply a negative voltage (for a NPN) to the base, the device will act as a zener diode with a voltage appr. 5-8 Volts.
Regards
Arne
They look like a v reg for the opamp. The reason two are used instead of one of the proper voltage is to get the power handling up. Try using two zeners in the 6 to 7 volt range 1W and you should be fine.
Used to do it at Threshold all the time. Works fine if you'reli_gangyi said:
looking for that voltage and use a suitable transistor. Back
then, I found them more reliable than the zeners we were
buying.
Guys, thank you all for the help, i`ve changed those zeners now, that i thought was the problem but the problem still exists, bugger! (aussie slang for sh--------------------------t!)
what i`ve changed so far are all the electrolytics, dc servos and those zenners, and measured most of the fuseable 10ohm/ 1mohm resistors on the advice of the old Adcom imorter here in Australia.
The problem that i`m still having is that there is too much current being pulled through R153 1.2k and R154 1.2k they get hot and start to smell,and the green leds D113,D114 in that same section, that their using as diodes are very bright compared to the good channel, but i`m getting good sine and square waves on the scope, and the bias is steady, however the dc offset is at 1volt! As you can tell i`m not a tech, but can usually fix things with persistance and help.
Any More Ideas as the Importer has none.
what i`ve changed so far are all the electrolytics, dc servos and those zenners, and measured most of the fuseable 10ohm/ 1mohm resistors on the advice of the old Adcom imorter here in Australia.
The problem that i`m still having is that there is too much current being pulled through R153 1.2k and R154 1.2k they get hot and start to smell,and the green leds D113,D114 in that same section, that their using as diodes are very bright compared to the good channel, but i`m getting good sine and square waves on the scope, and the bias is steady, however the dc offset is at 1volt! As you can tell i`m not a tech, but can usually fix things with persistance and help.
Any More Ideas as the Importer has none.
Hi George,
Correction...
Try checking the transistor Q103, Q102,Q104,Q105 - Q108
also Q115 - Q116.
Thanks
Correction...
Try checking the transistor Q103, Q102,Q104,Q105 - Q108
also Q115 - Q116.
Thanks
Yeah...used to drop the voltage for the opamp...while you are at it...replace the opamp...if the zeners are busted..the opamp might be as well...
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