M-3 Percussion Problem

[Guest]

Recently I noticed the percussion on my M-3 stopped working, when I have the drawbars on and hit the percussion ON button, the volume drops but I don't have any percussion. I figure that the drop in volume when the switch is on indicated that the switch is ok, I have checked all the tubes and they are all good and played with the percussion on the amp but get nothing...any ideas?</p>

</p>

Thanks</p>

</p>

John</p>

www.youtube.com/buddhashake
</p>

[fredy2]

Re: M-3 Percussion Problem

Check V7 percusive amp (6C4 tube) and V9 percusive amp tubes.

[fredy2]

Re: M-3 Percussion Problem



Not sure how you checked them... also check for the 205 volts to the second percussive amp. From the schematics I can find online, the circuits look simple. I would try injecting hum from a "antenna" of a few feet of wire at the grids of the percussive amps to verify they are working.</P>


Check the voltages on the astable V7 tube found on the schematics here:</P>


http://www.hammondb3organ.net/schema...mond/organs/m3</P>


There are several caps around the circuit and also a VERY high value resistor (47Meg). The real high value resistors are more prone to failure.</P>


You really need an osciloscope to troubleshoot this effectively. Check that cathode voltage on the 6C4 V7. I can barely read the schematic... looks like either 5.5 or 55 volts... That will be a fairly important one. It looks like they have an astable with feedback between the output transformer of V7 and the input transformer of V7... sure hope those transformers are OK... The cap from the grid to the cathode of V7 is pretty important for operation.</P>


When working on anything with high voltage take all precautions against shock.</P>
<P mce_keep="true"></P>

[bluetantra]

Re: M-3 Percussion Problem



Hi, John-</P>


I agree with Fred's first diagnosis about the tubes. Without a tube tester, you really can't determine the strength of a tube. The glow from a tube's heater doesn't necessarily indicate that it's operating as it should. Eliminate the easy stuff first and try replacing tubes V7, which is a 6C4, and V9, a 12AU7, with known good ones.</P>


John</P>

[Guest]

Re: M-3 Percussion Problem



Ahh thanks, I had tried switching tubes from another organ I have but maybe all the tubes on both are bad.
</p>

I do have a real old heathkit osciliscope 0-6 that looks just like this http://www.thebakken.org/ARTIFACTS/D...=W&amp;id=1944 But I can't get that working either.</p>

</p>

I play in 5 different bands and have 5 Hammonds that I have acquired over the years but quickly finding myself having to learn electronics to keep them working since I find it impossible in my area to even find someone that will even look at any of my organs to help me out....it's bad enough to find someone to help me load my van for a gig.
</p>

Thanks for the help, I'll check what I can find, the diagram was very useful......thanks again</p>

</p>

John</p>

</p>

</p>

[fredy2]

Re: M-3 Percussion Problem



Please feedback what the cure is so we can help the next person too !</P>


The old Heatkit scop is good enough to analyze this. I suspect the problem is around the V7 which appears to be a starved oscilator that actually generates the sound. Withthe scope look at the plate of V7and you should see a damped waveform if that stage is working. Checking the bias on the cathode is key to tube being good or a failure of a component in the area.</P>

[Guest]

Re: M-3 Percussion Problem



Problem fixed...after replacing the V9, 12AU7 tube with a third one, it started working again. The other tubes looked OK and glowed but I guess they just must have had something wrong with them. Thanks, you guys are a big help figuring out what tubes to look at, I guess I'm slowly going to have to learn electronics if I am going to gig with my Hammond organs since everytime I move them lately I come across some weird problem. It's bad enough I spend all the money I get off a band gig to pay for the Truck's gas...I can't afford a Hammond tech or a new organ! :)</p>

</p>

Much Appreciated!!
</p>

Thanks again</p>

John
</p>

[fredy2]

Re: M-3 Percussion Problem

You might want to swap back one of the bad ones and VERIFY that was the real cause. There is always a slight chance that rocking the tube to get it out mechanically disturbed something that was the real cause. Usually if the tube glows and does not turn purple, it will work at least a little bit in the function of V9. The 12AU7 has two sections so verifying BOTH sides are lit is important.