MN3005 Heating up!!!! Fake Chip??

[armdnrdy]

I've searched around the net, and have found numerous topics on fake chips from China, (after the fact!!) I've read about dead chips or relabelled chips that offer less delay stages, but I haven't found anything on the problem that I'm having. Maybe someone can offer some insight.

I did a build for an AD-80 using the factory schematics. I designed the board using Eagle with the AD-80 service manual board layout as a guide. Eagle's DRC check shows schematic and board are consistant. I visually traced and used a DMM for wrong component values, proper voltages, solder bridges, cold solder joints....everything checks OK.

The MN3005 heats up to the point that you can't touch it when I engage the effect. Is this a relabelled low voltage MN32XX?  I have 12 volts at pin 1 of the BBD.

Any help would be appreciated,

Larry

[MikeH]

What are the voltages on all of the pins?

Dumb question: It's not in backwards is it? 

[oldschoolanalog]

Does the circuit work (you didn't mention)?
Either way, the BBD shouldn't get hot. Not even a bit.
I posted test V's from a working vintage AD80 some time back. UTSF.
How about a couple of close up pix of the BBD in question? The fakes are pretty easy to identify.

[armdnrdy]

No it's not backwards, the IC is oriented correctly. As far as pin voltage readings go, I haven't been able to leave the power on long enough to get that far.

[Hides-His-Eyes]

Take the chip out and measure the voltages without it in there.

[oldschoolanalog]

http://www.diystompboxes.com/smfforum/index.php?topic=76582.0

Unplug the BBD and test.

[armdnrdy]

Okay, with the 3101 and the 3005 taken out, I have the following readings:

MN3005 location:
1=11.88
2=0
3=8.07
4=8.56
5=0
6=0
7=8.22
8=0

It seems compared to oldschoolanalog's readings, 3,4, and 7 are high. Any ideas?

[armdnrdy]

Here is the schematic that I used for my build.

http://www.sonicurbs.com/ibanezAD-80/ibanezad80.pdf

[Paul Marossy]

Did you use a verified PCB or some other method to build it? If you perfed it, maybe there is a mistake somewhere that is causing that IC chip to pull a LOT of current...

[armdnrdy]

Paul,

Some of the pins are at a higher voltage than oldschoolanalog's voltage readings. I used the factory schematic and Eagle cad to design the board. This is not by any means my first board. I've made flangers, compressors, and combined effects on one board. The board is verified as matching the schematic in eagle and by me visually. At this point, I am looking for a bad componant causing the over voltage.

[rustypinto]

Your voltage readings don't look out of the ordinary. You should be able to vary the voltage at pin 7 since it has a bias pot. If you install the MN3101, pins 2 and 6 should measure half of the supply voltage since these signals are the clocks at a 50% duty cycle, and pin 8 should be ~1V.

I do know that if the counterfeits are relabeled MN32XX series devices instead of MN30XX devices it should do something catastrophic because the polarity of the supply pins are opposite (NMOS vs. PMOS).

[armdnrdy]

I plugged in another MN3005 (unverified) and the MN3101 and adjusted the bias. Here are the voltages.

MN3005:            MN3101:
1=11.8              1=11.2
2=5.6                2=5.6
3=5.6                3=0
4=5.4                4=5.6
5=0                   5=5.2
6=5.6                6=5.8
7=5.7                7=5.8
8=.76                8=.76

The BBD voltages look good, while the oscillation circuit voltages of the MN3101 are way off. Does anybody know what this means? Bad driver?

[Paul Marossy]

Paul,

Some of the pins are at a higher voltage than oldschoolanalog's voltage readings. I used the factory schematic and Eagle cad to design the board. This is not by any means my first board. I've made flangers, compressors, and combined effects on one board. The board is verified as matching the schematic in eagle and by me visually. At this point, I am looking for a bad componant causing the over voltage.

Understood. But you still could have made a mistake somewhere. Just thinking of possibilites.

It might be an out of spec chip that is the problem. Kind of like those NTE parts probably are (out of spec factory rejects), but they stamp their own name and numbers on them instead. It still seems to me like the MN3005 is drawing too much current (why it gets so hot), which could theoritically be a faulty out of spec IC chip.

Do you have any other MN3005s to try?

[armdnrdy]

Paul,

I had another MN3005 that is not a verified working component that I dropped in. With the IC being "in the circuit" it lowered the questionable voltages on pins 3 and 4. I also adjusted the bias trimmer for pin 7 to a working AD-80 voltage level. The BBD voltages now look correct. The problem now seems to be the clock driver oscillation circuit. (pins 5,6, & 7) The MN3101 pins 5,6,&7, should read:
Pin 5 = 11 volt range
Pin 6 = under 1 volt range
Pin 7 = 9 volt range

If you look at my previous post, you'll see that those pins are off considerably. Any input would be appreciated.

[Paul Marossy]

Yeah, it looks like maybe the problem is with the MN3101. Hopefully someone well versed in those IC chips will chime in...