Lowery Organ Repairs

You might be in luck; here is a source of Lowrey manuals: http://www.organservice.com/lowrey/LowreyManuals.htm

Thanks for your effort --I will give it a try

Thanks

I'm afraid you have a long-term project... This instrument is a component-cemetery. The boards contain lots of tiny decoupling capacitors and after 25-30 years those capacitors tend to become shortcuts, especially the tantalum ones. First it seems like a power supply problem, the heat sinks starts to become warmer and warmer, then the fuses blow on the low-voltage side.

The only way to fix the problem is removing and replacing all of decoupling capacitors...

Good luck!...

"The only way to fix the problem is removing and replacing all of decoupling capacitors..."

You really know how to cheer someone up

I had similar problem with a Böhm Musica Digital 800. I had to replace about 60 capacitors...

I would have to respectfully disagree about tantalum capacitors, we have product in the field that uses these, and they rarely short out from aging. Now, electrolytics, that's another story. I have completely recapped an early camcorder, a Toyota van audio amplifier, and Tektronix O'Scope, but only the electrolytics. I've never had a problem with tantalums. They are a solid electrolyte, vs liquid in the canned electrolytics, so they don't dry out. My opinion, of course.

Tom D.

Either you were lucky or I was unlucky, these are some tantalic capacitors removed from the Böhm:

Maybe the problem is that the Böhm (and probably the Lowrey too) is fairly hot inside because the power amplifier (50 W) and the stabilised, analogue power supply heats the cabinet.

And these parts are indeed shorted? I have yet to see a dipped tantalum part that shorted. I've seen them burst into flames when installed backwards , but we've never had a problem with field returns as far as these are concerned. I don't recognize the manufacturer of these in your picture, we've pretty much always used Kemet and Sprague exclusively, maybe that's the difference.

Tom D.

I don't know who the manufacturer was. Those are shorted...

The original symptom was that the current protecion of the 5 V and +15 V power supply tripped. There are several boards in the Böhm (the different functions are separated to different boards) and I had to go board by board to find the shorted capacitors. I disconnected the internal power supply and supplied the actual board with an external supply with the nominal Voltage but lower current limit. The current limiter tripped and the faulty capacitors started to warm-up. I removed them and replaced with a low-ESR 105 C° ambient temperature electrolytic capacitor. Then, I went for the next one... I hated that job but the instrument was from a friend of mine...

I don't know Kemet but Sprague is well known and respected brand in Hungary.

Lowrey D325 has a dual power system. One transformer (T1) is for the signal generating system, the other one (T2) is for the power stages. The T1 circuit has a fuse, but it's behind the "power indicator" lamp. T2 does not have any fuse on its primary side but there are separated fuses for every power amplifier. First you have to determine which fuse(s) had blown. If T2 operates properly (all the five +55 V present) you probably have capacitor problem in the "logic", signal generating side, as writen above...