BAJA Wet Cat analog delay (mini version)

rocklander · Post by **rocklander** » 08 Apr 2009, 23:25

"hello sailor" would be a more kiwi thing to say wouldn't it?

WeAre138 · Post by **WeAre138** » 10 Apr 2009, 04:01

Hi, I've been a lurker over here for a while but this is probably my first post. I've run into a major problem while building this pedal. I just finished soldering it all together and after powering it up the first time, the 22 Ohm resistor began to smoke and burn up on the board. I built the MN3205 version. After close examination, none of the pads on the pcb have solder bridges. I replaced the burnt resistor and the same thing happened again. Is anyone else running into this problem?

KHELSTROM · Post by **KHELSTROM** » 10 Apr 2009, 06:16

WeAre138 wrote:Hi, I've been a lurker over here for a while but this is probably my first post. I've run into a major problem while building this pedal. I just finished soldering it all together and after powering it up the first time, the 22 Ohm resistor began to smoke and burn up on the board. I built the MN3205 version. After close examination, none of the pads on the pcb have solder bridges. I replaced the burnt resistor and the same thing happened again. Is anyone else running into this problem?

Post some pics of both sides of the board.

WeAre138 · Post by **WeAre138** » 10 Apr 2009, 09:01

Here are some pics of the board. I noticed a few solder bridges, but only on pads that were connected by the traces. Please excuse the crowded space on the board.

KindaFuzzy · Post by **KindaFuzzy** » 10 Apr 2009, 13:24

Mine did that the first time too, I ended up putting two 47 ohm resistors in parallel since I didn't have a 22 ohm 1/2 watt. That seemed to do the trick.

WeAre138 · Post by **WeAre138** » 10 Apr 2009, 16:52

KindaFuzzy wrote:Mine did that the first time too, I ended up putting two 47 ohm resistors in parallel since I didn't have a 22 ohm 1/2 watt. That seemed to do the trick.

Thanks for the tip. Hopefully that solves my problem.

KHELSTROM · Post by **KHELSTROM** » 10 Apr 2009, 18:20

I think there is an error in the PCB. It has pin one of the MN3102 going to ground and pin three going to Vdd. Correct me if I am wrong but I believe this should be the other way around. Look at the schematic for the DM-3.

On another note... When I was comparing the schematics of the DM-2 and DM-3 I noticed that the MN3101 in the DM-2 has a diode between pin one and Vdd but on the MN3102 of the DM-3 the diode is between pin three and ground. Why the change?

bajaman · Post by **bajaman** » 10 Apr 2009, 21:55

Good spotting KHELSTROM.
My mistake - it was late at night when I drew it up!!

I will correct it tonight and upload the correct pin connections.
WeAre138 - try cutting the tracks near the IC pins and use some small bridging wires to transpose the pin 1 and pin 3 connections - it should work then - my apologies for this error.
cheers
bajaman

ps: you should not have to change the diode at all - it is oriented correctly and it does not matter whether it connects to positive or ground pins of the IC.

WeAre138 · Post by **WeAre138** » 11 Apr 2009, 03:18

Thanks for all of the help on this pedal. I'll try to make the corrections to my pcb and post the results.

bajaman · Post by **bajaman** » 11 Apr 2009, 11:26

IMPORTANT

I just updated the composite and PCB layout files for the MN3205 version.
Please accept my apologies for any inconvenience caused by using the original incorrect artwork, and once more thank you to KHELSTROM for bringing the errors to my attention.
regards
bajaman

WeAre138 · Post by **WeAre138** » 13 Apr 2009, 02:49

I've made the corrections to my pcb, which seems to have fixed the burning resistor problem. The main problem that I'm having now is that no matter how much I adjust the bias and cancel trimpots, no delay is produced. Does this mean that my bbd chip might have been fried as well?

bajaman · Post by **bajaman** » 13 Apr 2009, 04:18

No, but the clock driver may have been damaged (MN3102)

WeAre138 · Post by **WeAre138** » 13 Apr 2009, 07:04

I tried switching out the MN3102 chip but still no change

KHELSTROM · Post by **KHELSTROM** » 13 Apr 2009, 13:17

WeAre138 wrote:I tried switching out the MN3102 chip but still no change

Did you switch the polarity of the diode on the MN3102 after wiring up the jumpers?

WeAre138 · Post by **WeAre138** » 13 Apr 2009, 15:52

I think I have it oriented correctly, unless if there are more errors on the layout that I keep missing.

bajaman wrote: WeAre138 - try cutting the tracks near the IC pins and use some small bridging wires to transpose the pin 1 and pin 3 connections - it should work then - my apologies for this error.
cheers
bajaman

ps: you should not have to change the diode at all - it is oriented correctly and it does not matter whether it connects to positive or ground pins of the IC.

WeAre138 · Post by **WeAre138** » 14 Apr 2009, 06:02

KHELSTROM wrote:
WeAre138 wrote:I tried switching out the MN3102 chip but still no change
Did you switch the polarity of the diode on the MN3102 after wiring up the jumpers?

I tried switching the polarity of the diode, but still no change.

bajaman · Post by **bajaman** » 14 Apr 2009, 07:46

The diode polarity is correct as it was on the board layout.
Okay - here we go.
1. Do you have a signal generator, oscilloscope, multimeter etc???
bajaman

bajaman · Post by **bajaman** » 14 Apr 2009, 07:49

2. set both trimpots to halfway to begin with.

bajaman · Post by **bajaman** » 14 Apr 2009, 07:52

3. what are the voltages on the first IC pins (IC1 - OP275 or similar dual op amp - eg: TL072, 4558 etc.)???
bajaman

Dan N · Post by **Dan N** » 15 Apr 2009, 00:26

The two 100K resistors on the Cancel trim go to ground on the 3205 DM-2.