Bottlehead Forum

Bottlehead Kits => Legacy Kit Products => Paramount => Topic started by: Paully on March 05, 2011, 02:49:17 PM

Title: Checking LED on soft start - two won't light
Post by: Paully on March 05, 2011, 02:49:17 PM

I put a good bit of solder on my LEDs so I thought I would check them to make sure I didn't burn any out.  Two won't light.  But oddly it is the same two on each board.  With the boards oriented as instructed it is D1 on the left hand side of both boards.  Any reason they shouldn't light up?  If not, I will replace them with some extras I have.  Thanks!

Title: Re: Checking LED on soft start - two won't light
Post by: Paul Joppa on March 05, 2011, 06:25:15 PM

Have you adjusted the trimmer for the correct plate voltage?

Title: Re: Checking LED on soft start - two won't light
Post by: Paully on March 06, 2011, 03:14:00 AM

I haven't even installed the boards.  I was just using my voltemeter.

Title: Re: Checking LED on soft start - two won't light
Post by: Brillo on March 06, 2011, 09:38:13 AM

Not ruling out that there may be an issue Pauly, but these two LEDs take a little while to 'warm up' at first.  I thought I had an issue when starting in on the voltage checks described in the manual, but after about a minute these two LEDs were glowing brightly.   

Title: Re: Checking LED on soft start - two won't light
Post by: Paully on March 06, 2011, 10:04:38 AM

Cool, thank you!

Title: Re: Checking LED on soft start - two won't light
Post by: Paul Joppa on March 06, 2011, 12:10:19 PM

Oh - OK. It's the soft start delay, which takes 20 seconds if you apply 300 volts ... got to charge up that 10000uF cap before the LEDs can glow.

Title: Re: Checking LED on soft start - two won't light
Post by: Paully on March 06, 2011, 02:08:31 PM

Heh, heh, I feel kind of silly now!  It was probably going to take my voltmeter a while to charge that capacitor...

Title: Re: Checking LED on soft start - two won't light
Post by: Grainger49 on March 06, 2011, 02:17:48 PM

I don't know the schematic, is the capacitor in parallel with the LEDs that are not lighting?

Title: Re: Checking LED on soft start - two won't light
Post by: Paul Joppa on March 06, 2011, 03:31:55 PM

Quote from: Grainger49 on March 06, 2011, 02:17:48 PM

I don't know the schematic, is the capacitor in parallel with the LEDs that are not lighting?

Yes it is. It charges slowly, from the LED bias current, preventing the LEDs and transistors from turning on until it is charged.