Author Topic: Question about a BBD chip  (Read 1115 times)


Question about a BBD chip
« on: August 06, 2018, 09:16:13 AM »
So this isn't technically a build-your-own project, but this looked like the only place for my question. Also, warning, this may seem pretty noobish...

I'm trying to troubleshoot an MXR flanger that isn't flanging. After poking around in it, I saw that the MN3204 gate supply voltage doesn't seem to be at what the datasheet says it should be. I'm getting 9.7V at the drain, and 1.6V at the gate. The datasheet says the gate supply voltage should be 14/15*drain supply voltage, which would be 9.05V at the gate.

My question is, could this be a sign that the chip is bad? Or am I completely misunderstanding the datasheet? Here's the sheet I'm looking at, and the table I'm getting this from is on the second page:



Re: Question about a BBD chip
« Reply #1 on: August 06, 2018, 10:18:46 AM »
Hi and welcome,

it's unlikely that one mosfet got shorted...
MXR doesn't use MN's clock chip, then Vgg must be achieved by resistors. It should/might have one capacitor for smoothing: check that
"NOT FLAMMABLE" is not a challenge


Re: Question about a BBD chip
« Reply #2 on: August 08, 2018, 01:38:10 AM »
Thanks for the reply, and the welcome!

I've checked the cap that connects directly to Vgg. It tested OK, but I swapped it out just to be sure, and now Vgg is actually reading 0v. Maybe the 1.6 it was reading before was leftover energy stored in the cap (don't know if I'm saying that correctly...)?

Anywho, I'm in the process now of tracing the signal back from the cap to see if I can find where I'm getting 0V, and hopefully that'll be my culprit.

Thanks again for the help!