Help!! LM317T Filament Heater Problem - diyAudio
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Old 17th December 2010, 07:10 PM   #1
ron944 is offline ron944  United States
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Unhappy Help!! LM317T Filament Heater Problem

Hi, I did a complete rebuild on a Counterpoint SA-3.1. When I fired it up I am getting no voltage to the heater filaments. The high voltage is fine. I put in a INXYS full wave bridge which then goes to a 1000uf cap and then to the in of the LM317T. Output from the LM317 goes to a 110 ohm and then a 402 ohm resistor. The ADJ pin goes to a 10uf cap and then to a point between the two resistors. I have 15v coming out from the bridge rectifier (my ac is a little high 123v)and 15v showing at Vin on the LM317T but 0 volts on the Vout and ADJ pins. Can something on the load side be causing this or can the delay circuit be causing the problem (the led goes green after 30 seconds and I have high voltage readings). I tried three different LM317T's the back is isolated from the chassis with thin rubber. I am going to unwire the Vout and ADJ pins and see if there is an output voltage. Any Ideas will be helpfull Thanks, Ron
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Old 17th December 2010, 08:00 PM   #2
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Check the datasheet for connections on the LM317. (Tab to back and pins down it should be adj-out-in for TO-220. This differs from the 78XX series.) With adj to GND it should give 1.23V out. Keep in mind that filaments have a high inrush current.

Last edited by boyofwax; 17th December 2010 at 08:03 PM.
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Old 17th December 2010, 09:03 PM   #3
ron944 is offline ron944  United States
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It is a TO-220 package with the pins as you described. I will check adj to ground and see what Vout reads.
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