Moodring dwell control not working properly

[sumac]

Hello all

after few trouble-free madbean builds I finally arrived at a problem! Just finished a moodring reverb and it works and sounds nice, but there is problem with dwell control - when turned up beyond about 12 o'clock it causes feedback kind of weird hum which gets progresively louder even when you dont touch the strings.. You have to turn it down otherwise the hum just gets louder and louder.. same thing happens even in the when effect is bypassed! (effect is wired for buffered bypass) Checked voltages and they look OK - most are bit higher than published but not much, except for IC3. On pin7 I have: 1.5VDC and on pin8: 2VDC and oscilating..

Any idea what could be the culprit? Maybe a bad PT2399?

thanks
martin

[madbean]

Those voltages on pins 7 and 8 seems abnormally high. Any chance of a bad cap or two there?

On the dwell control - please carefully inspect that you have used the correct values for R31 and R30. Also, check ground continuity on lug 1 of the Dwell pot.

[sumac]

Thanks!

I've checked the caps and resistors you've suggested and they all seem fine.. Then I swapped few PT 2399 I had laying around and found that with some - the voltages are closer to what they should be.. (best IC measures around 1VDC on pins 7 and . So the problem is most likely connected with my bad PT2399 (I bought bunch of them some time ago for cheap and now I see why they were so cheap..) Also the problem with Dwell knob is much less noticable now with better IC, however its still there.. Also I get quite a lot of noise as I turn up the ring pot (even with internal trimpot set all the way down) so maybe that is also caused by the bad IC?

will order some fresh ICs and we'll see
thanks again
martin