Static problem in H-395

[Bobmann]

Midway through a song, I became aware of a loud noise...it was as if a switch was flipped on.
There is now a constant static/hissing sound; like the white noise you hear between AM radio stations.
It can be heard from both channels, all 3 speakers. Makes no difference vibrato or percussion or reverb on or off.
The static volume changes with the swell pedal...with pedal volume at minimum, the static is barely noticeable.
With all drawbars in, the static is there; I pulled each drawbar out and got a tone, (both sets of DBs, both upper and lower) but no difference in static. Static is also heard through the Leslie, but I unplugged the Leslie until I can get this resolved.</P>


I have a spare H in the shop; it was working when I pulled components out. I switched out the entire amp and all tubes, the power supply and all the tubes, and the percussion amp. None of this made a difference. I unpluggedt the vibrato scanners at the connector. I pulled all the connectors apart and gave them a shot of De-Oxit...still no change.</P>


Anyone have a suggestion to where to look next? Any thoughts on unplugging all the connectors I can find to see if the static goes away, then re-connecting them until the noise returns? Could this cause any damage to any components?</P>


Thanks for the assistance
Bob</P>

[bluetantra]

Re: Static problem in H-395



Bob-</P>


Do the "Vibrato Upper" and "Vibrato Lower" tabs have any effect? My guess would be that you've got a problem on one of the 8 pre-amp boards. I'm slowly but surely refurbishing my H-182. I was given some very good advice in another thread that I'll re-post here:</P>


If the other power supply did the same thing I would suspect a problem with the load like a shorted filter cap on one of the preamp boards. You could monitor the voltage while disconnecting the filters one by one. </P>


After you find that problem, I would replace all plate load resistors in the amplifier. They are always bad and cause weak or dead channels. I would also replace the electrolytic caps in the amp. They are mostly used as bypass caps and are usually bad. There are two used in creating the bias voltage for the bass channel outputs.
</P>


The preamp boards should have all their electrolytic caps replaced. Some are used as filters and can short the power supply. Some are coupling and effect the quality and volume.</P>


You will be amazed at the transformation when these steps are taken.</P>


The whole thread is here: http://organforum.com/forums/permali...ead.aspx#61457</P>


I'm still working on the main amp, but replacing all the caps in the pre-amps, percussion, and pedal pre-amps made a big difference already.</P>

[Bobmann]

Re: Static problem in H-395



Thanks for the assistance.</P>


Turns out there must be a bac cap on the non-vibrato pre-amp, as swapping it with one from my donor organ fixed it.</P>


I will start replacing all the other caps, as it appears that it is just a matter of time before others go out.</P>


Again, thanks for the help.</P>


Bob</P>

[bluetantra]

Re: Static problem in H-395



Funny... the non-vibrato pre-amp was the first to go in my H-382. I did the same as you and swapped one from a donor. The pedal pre-amp was next to give up. While it has worked for a few months, I can tell it's getting weaker and will need new caps soon. I suppose it'll be next in line after the H-182. Now that one has been a labor of love... wonky electronics, rattling and broken keys, stubborn pre-sets, rust from mouse pee, bad tubes, chewed wires... in other words, a real learning experience.</P>