The Organ Forum

I'm having a problem with a '69 H-182; several, actually.  It starts and runs fine, all tubes test very good on both the amplifier and power supply chassis (weak ones replaced).  I get nothing from the pedals, percussion is dead, volume overall is weak compared to another H sitting beside it, vibrato gets weaker than non-vibrato, dual vibrato, chorus and celeste seem to be out as well.  I think the problem is one or more of the pre-amps, as well as possibly the power supply.  Testing voltage to the 8 pre-amp cards, I get 5.5V from the orange line to ground, but the schematic shows 25V should be powering all these pre-amps.  The green jumper across all 8 boards reads 109V to ground, not so far from the 100V shown on the schematic.  I'm finding about 6.5 into both the pedal and percussion pre-amps.  High voltages at the power supply run 50-100V higher than on the schematics.  I've tried a spare power supply, but I get about the same results; therefore I'm assuming both power supplies have issues.  I've already changed all but the non-vibrato pre-amp with boards pulled from another previously working H and one NOS board along with the pedal and percussion pre-amps.  Am I looking at a power supply re-build?  If so, I could really use some advice.  George?  Fredy?  Somebody? Help?!....

Thanks in advance,

John

 

 

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"I first saw it sitting in a corner in a Los Angeles studio. I had never seen anything like it before. I put my hands on it... and I knew this was for me." - - - Ethel Smith

From this site:

http://www.captain-foldback.com/Hammond_sub/hammond_schematics.htm

From the H100 schematics:

50-6 drawing shows the 25 volt power supply.  Should be very easy to isolate the cause of the low voltage.  Probably a bad cap, resistor, or diode pair.  Shorted C706 section or the 710 ohm resistor could be the problem.  Don't be fooled by having some voltage and not zero that the resistor could not be open as there are often sneak paths.  If you find 25 or so volts across the resistor, look for a bypass cap shorted somewhere in the loads on the 25 supply.

Since the supply to the resistor is something over 30 volts on the high side, that is the first to check.

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Fred

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.

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.

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.

You will be amazed at the transformation when these steps are taken.

George

 

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Organs

Hammond B-3/145
Hammond Super B (MIDI Controller)
Yamaha FX-1 - TM-1 x 2

Synths

Korg Triton Pro
Yamaha P-80
Native Instruments Soft Synths;
Akoustik Piano, Electrik Piano, B4II,
FM-8, Pro-53, Massive, Absynth,
OPXpro, Mtron

I will tell you how I troubleshoot some of these problems of shorts or excessive loading.

I use a current limited supply set below the normal voltage and drive a reasonable current into the problem feed line.  The I use my calibrated temperature sensor (finger) on suspect components.  The trick is to use enough current but a safe level for wiring and board traces.  Keep eyes protected in case an electrolytic blows.  Always have the max voltage of the test supply well below the normal level that is carried on the line.

Using this method and one of those infared thermal meters from Harbor Freight I was able to isolate an are on a large mixer board quickly... then the calibrated finger homed in on the problem.  That one was actually a hole burned in a board that had carbonized under an IC.

Another thing I use is a millivoltmeter to trace the point of lowest voltage along the feed.  Where the voltage is lowest is very close to the problem component.

The last thing in my bag of tricks is a special HP current tracing probe... expensive but handy...

 

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Fred

Thanks guys.  I guess the only way to get this done is to jump in with both feet, so to speak.  I've spotted a difference in the schematic and actual parts in use.  C705 is shown in the schematics as a 100mfd/50V, but both the '69 and '72 power supplies have 500mfd/30V instead.  My copy of the schematic had this change marked already and references an old service bulletin.  It's not marked on Captain Foldback's copy.  The '69 power supply has a 25mfd/50V cap and a big diode that's mounted through the chassis while the '72 power supply has neither of these.  They aren't on the schematic at all.  Given a choice, would you choose to go through the original 1969 power supply and amplifier or the spares I've got from a 1972 model, or would it really make that much of a difference?

John

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"I first saw it sitting in a corner in a Los Angeles studio. I had never seen anything like it before. I put my hands on it... and I knew this was for me." - - - Ethel Smith

Thanks, Fred.  I really appreciate these troubleshooting tips.

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"I first saw it sitting in a corner in a Los Angeles studio. I had never seen anything like it before. I put my hands on it... and I knew this was for me." - - - Ethel Smith

fredy2:

my calibrated temperature sensor (finger) on suspect components

 

That came in real handy when I found the bias voltage too high on a finned transistor on the vibrato drive pre-amp.

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"I first saw it sitting in a corner in a Los Angeles studio. I had never seen anything like it before. I put my hands on it... and I knew this was for me." - - - Ethel Smith

Given the startup voltage for that 705 cap, 30V is pushing it... and 50V is pretty high the other way.  Electrolytics should be run at least above 50% of their rated voltage for good design practice... Yet the 30 is right on the edge at the other end.

It sounds like somebody has hacked the supplies a bit... But you should be able to trace the problem fairly quickly.  Some of the resistors of that vintage equipment used wirewounds that were in a metal channel... I found one of them went bad once. 

Electrolytics are always suspect...

Also look for foreign objects like steel wool shards...

One person found somebody had connected the 25 volts to the vibrato with a jumper... Only thing I could think of they were trying to blow dendrite whiskers out of the unit...  One is liable to find anything in these organs...

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Fred

After poking around a bit in the power supply, I found all of the big 10W resistors out of tolerance (R701,703,704,705).  I went over the schematics and the amp to come up with a sizeable list of capacitors to replace along with the four resistors.  I found most everything I think I'll need through Mouser and Antique Electronic Supply.  A couple of snags, though.  C703 is a multi-section cap of 40mfd/400V, 100mfd/350V, 100mfd/150V.  I can't seem to locate anything remotely close in a multi-section.  Replacing this with 3 separate axial types is the only solution I can come up with.  C706, a 1500mfd/50V, doesn't seem to be available in the can type either, but I can find axial and radial.  Any tips on trying to keep the appearance original would be great.

On the main amplifier, I'm having trouble finding replacements for C319 and C321 - both 50mfd/10V.  These are in the pre-amp circuit that drives the external tone cabinet.  The closest value I can find is 47mfd/10V.  Will this work?  I have a 222 to hang on this organ once it's finished.

I also plan to replace all the electrolytics on all 10 pre-amp boards.  No problems finding those values.  This is my biggest project list yet with Mouser.

Why would Hammond design this power supply with solid state components just to produce the 35V for the pedal sustain solenoids?  Couldn't this have been done using tubes and other passive components like the rest of the power supply?  Sorry for any seemingly stupid electronic questions.  My formal technical training was in HVAC, Appliance Repair, and Cosmetology.  I really do appreciate your help.

John

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"I first saw it sitting in a corner in a Los Angeles studio. I had never seen anything like it before. I put my hands on it... and I knew this was for me." - - - Ethel Smith

47mfd IS a 50mfd. In other words, there was a time when cap values were whole numbers. 10, 20, 30, 40, etc. That was changed to 10, 22, 33, 47, etc. At this moment, I don't remember why. Maybe Fred knows??

There are many solid state components in the H-series. It's considered a hybrid. Tubes and solid state. It was a transitional model as things of that day were slowly changing to transistors.

George

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Organs

Hammond B-3/145
Hammond Super B (MIDI Controller)
Yamaha FX-1 - TM-1 x 2

Synths

Korg Triton Pro
Yamaha P-80
Native Instruments Soft Synths;
Akoustik Piano, Electrik Piano, B4II,
FM-8, Pro-53, Massive, Absynth,
OPXpro, Mtron

The power resistors are probably 20% tolerance and are unlikely to be critical values at all.  If you find one wide open, then of course replace... don't waste money on them...!!!!

The capacitor values are not critical relative to 47 versus 50... Electrolytics of that vintage often have tolerance ratings of +100%/-20 % anyway...

Tube rectifiers are for high voltage and currents that are much lower than solenoids would require.  A lot of power would be wasted in heat to try to generate solenoid power using vacuum tube rectifiers.

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Fred

The value of capacitors and resistors were chosen somewhat so that for a given tolerance, the parts could be "graded" into bins without having to throw some away that could not be marked a value in the list and still be within one of the standard tolerances!!!

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Fred

Thanks, guys.  It makes more sense now.  I think I can finish my parts list.  But before I really get started on this H, I've got to finish the Wurlitzer 4100.  New caps for it should be here next week.

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"I first saw it sitting in a corner in a Los Angeles studio. I had never seen anything like it before. I put my hands on it... and I knew this was for me." - - - Ethel Smith

I have a question about replacing a capacitor with one of a slgihtly higher voltage.  The Pedal and Percussion pre-amps on this organ each use a 500mfd/3V capacitor.  The closest I can find at Mouser is 500mfd/16V.  Would this value work, or do I need to keep looking for the exact replacement?  Again, thanks for your input.

John

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"I first saw it sitting in a corner in a Los Angeles studio. I had never seen anything like it before. I put my hands on it... and I knew this was for me." - - - Ethel Smith

You can safely go higher, just not lower.

George

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Organs

Hammond B-3/145
Hammond Super B (MIDI Controller)
Yamaha FX-1 - TM-1 x 2

Synths

Korg Triton Pro
Yamaha P-80
Native Instruments Soft Synths;
Akoustik Piano, Electrik Piano, B4II,
FM-8, Pro-53, Massive, Absynth,
OPXpro, Mtron