Allen ADC Amplifier Module Repair

[myorgan]

Folks,

This thread is branched off the thread about my ADC-5400 I started when I obtained the organ a while ago. As John and I get the process down-pat for the diagnosis and repair of my failed ADC Amplifier Module (obviously others can chime in), we'll post the results here so the detail of an ADC amplifier module is memorialized for others to use.

To start, would it be safe to say the first thing to exercise is caution? I know in the past, it has been quite easy for a person to get quite a shock while working on an amplifier. Is that still true for the ADC modules? If so, which parts should I avoid?

Thanks in advance to those who positively contribute to this thread.

Michael

P.S. Correct me if I'm wrong folks, but is it true Allen no longer repairs the ADC amplifiers, rather, they substitute a customized AM-100 in its place for a dual ADC amplifier?

[tucsondave]

The first and easiest test is to remove power from the amp, connect an ohm meter across the audio input then turn on the organ to see if the internal mute relay is opening. Should read 1 meg when mute voltage applied.
Amps run on +45 and -45 volts.
No ADC repair = true.

td

[indianajo]

To start, would it be safe to say the first thing to exercise is caution? I know in the past, it has been quite easy for a person to get quite a shock while working on an amplifier. Is that still true for the ADC modules? If so, which parts should I avoid?

Read the safety sticky thread. One doesn't try to idenify the high voltage parts. One removes rings necklaces and jewelry, as 1 v can burn a finger to char through a ring. One touches any medium energy circuit with only one hand at a time. 25v from one hand to the other, can stop your heart, see the pig electrocution studies. 450 v in one hand bites a little. 450 v from finger to thumb is something I won't forget, but wasn't dangerous, just annoying. Use a ground alligator clip lead for the negative on the meter so you can use only one hand. Use a lot of light and don't work distracted by phone or friends.
Look for assymetric power supplies first thing (e-caps are usual culprits). Then input and output of op amps not all the same DC voltage, unless used as LED lamp drivers or something similar. There are more loose connections and oxidized pins in sockets than op amp failure unless 2900/3900/3301 norton op amps, known culprits. Parts datasheets are available for download on datasheetcatalog.com
Happy hunting.

[myorgan]

Unfortunately, it's been a month since my last post on this thread, and I STILL haven't had time (or weather) to get to the organ in the garage. At least 3 of the major performances are out of the way, so I hope I'll have more time in the coming weeks.

A question I forgot to ask is about a temporary amplifier replacement. I received a dual AM-100 amplifier with my 505B (MOS-2) organ when the Rodgers dealer removed two of the S-100 amplifiers for another project (I presume). Can the AM-100 from the MOS-2 organ be used as a temporary amplifier on an ADC-5400? Presently, I use the AM-100 as the amplifier for my Allen Ensemble when connected to the ADC-4300, but can re-locate it if needed. Theoretically, I think it's possible because on the ADC, the expression takes place in the cage rather than through the expression channel on the amplifier. I just want to check before I go that route.

Thanks so much for your advice.

Michael

[jbird604]

You can try it, no harm in that. The AM-100 was built in various configurations, some for line level (ADC) and some for the unique MOS level. However, some MOS systems also had line level amps, as with the mixture channels of the larger models, so the AM-100 you have may work just fine with an ADC organ. Or it may have way too much gain and therefore sound distorted. Just start with the volume barely cracked open, on the chance that the gain is too high.

If it proves to be high gain. you could get a pair those "attenuator" devices sold by Harrison Labs for the purpose of connecting standard line level reverb units to MOS amps. This would be an "off-label" application for these, but it would definitely work. I have made my own homemade version of these attenuators for this very purpose -- to run a line level signal into a MOS amp.

[myorgan]

If it proves to be high gain. you could get a pair those "attenuator" devices sold by Harrison Labs for the purpose of connecting standard line level reverb units to MOS amps. This would be an "off-label" application for these, but it would definitely work.

John,

Thank you for the idea. Those attenuators certainly won't break the bank as a new amplifier would. I believe I'll try it--now just for the time to try it, as the next week or two are quite busy.

Michael

[myorgan]

Update:

Well, I went to remove the Triple ADC Amplifier from the organ, and it readily moved when I touched it. As I get more and more into this organ, the less respect I have for the Allen Dealer/Repair organization that maintained it. Only one bolt was holding this amplifier in place from below, and it fell out onto the CR power supply when I touched the amplifier. I found a 2nd bolt next to the CR power supply that had previously fallen out. The other 2 amplifiers were screwed from above with 4 screws to the shelf. This is all a bit disconcerting to me, as I transport the organ regularly.

When I took the amplifier apart, there were only 2 screws remaining which anchored the sides of the amplifier to the chassis, and one of the 2 center screws on top was missing as well--all at the back of the amplifier where one couldn't see when (s)he looked. The other amplifiers had all 4 (6) screws. All that was holding the amplifier to the chassis were bits and pieces of the black tie-downs used to secure cord running throughout the organ.

I removed the offending module from the organ, and the 4-prong power and data modules almost fell out in my hand--they were not secured well at all. I checked all the caps to make sure they were solidly anchored, and they were all solid, as was everything else on the module. No obvious damage to the amplifier module could be seen (photos below).

So, I re-assembled the amplifier as best I could with the screws I had, installed it in the organ (with no power to the amp), plugged the organ in, and turned the organ on to be sure it worked. So far, so good. I then plugged in the amplifier and turned the organ on again, and there was a loud hum (I couldn't tell if it was coming from inside the organ or from the speakers right next to me), so I immediately turned it off. I unplugged the amplifier and attempted to turn the organ on again, and had no power--the GFI had tripped.

So, I tried connecting everything again with the organ off, and the moment I plugged the amplifier in, everything went dead (with the organ off). I checked the GFI, and it had again tripped. For the next time, I turned all the gain controls to zero, and tried again.

This time, I had my wife listen for the GFI tripping, and proceeded methodically connecting one thing at a time. Nothing happened. So I turned the organ on with the gain controls on Zero, and the same hum happened again, but this time with less power. The GFI didn't trip this time. I immediately turned the organ off, removed the amplifier, and looked inside for damage--none.

I'm stumped--not sure if it's the module with its lose disconnections, the gain pots, or somewhere in the mute relay. I think it's time to call in a professional. Agree, disagree, thoughts?

Michael

[jbird604]

Yikes! You're braver than I am. I wouldn't have gone through all that checking, once it hummed and kicked off like that! Also, to prevent any possibly damage to the organ, do your testing of the amp on a table top instead of inside the console. Just plug it into a power strip, then you can switch the AC on and off instantly as needed. Any escape of smoke, of course, calls for an instantaneous cutting of the power! But you can safely test the amp on a table top, with or without speakers connected. If you need to un-mute the inputs, use two 6 volt batteries wired in series to provide 12 volts for the relays, observing the + and - terminal markings.

I hate to hear that the amp was so poorly held together. That isn't good at all. At least there wasn't any damage to other parts of the organ. You can make sure to bolt it down properly when you put it back into the console.

Now, the black cage cover not being attached with all its original screws is no big deal. That is simply a cover to keep hands out while in operation. As long as it doesn't droop and touch the amp modules, don't worry about it. Or get some small screws and put them into the empty holes. Of course, Allen wouldn't have put the screws in there originally if they didn't think they were needed, so I do suggest getting some replacements.

But if the module itself was not firmly screwed down to the chassis, that is a big issue. The module has to transfer heat to the larger unit or else it will overheat quickly. It should have several large screws holding it in place, and there should be a coat of heat-sink compound at the mating surfaces. If you don't have all the screws, take one to the hardware store and get some more.

Also, if you're saying that the small circuit board itself was not securely screwed to the module chassis, that is also a problem, as the power transistors are soldered to the board but screwed to the metal part for heat transfer. So get some replacement screws for that too, if they are missing. Check to make sure that none of the power transistor pins got bent, and that none are accidentally making contact with some other metal part.

As to your circuit-breaker tripping, double-check to make sure the power and signal connectors are correctly positioned and that they are not pushed on backwards. I'm concerned that they were loose when you opened it up. They may have been damaged by a previous "fixer" who tried to push them on backwards. So use a good working amp for comparison and make sure that they are properly oriented. If necessary, use a small thin tool of some kind to bend the springy things inside the plug so that they will hold on tightly to the studs that stuck out of the amp module circuit board. Everything should fit up snugly and make perfect contact.

As I mentioned in an email to you, the modules in your AM-100 amp are identical to the ADC modules, so you can put one of those in place of the defective one to get your organ going again. Just make sure that the connectors are on there correctly so as not to damage another module!

Now that I'm on the mend from my surgery, I might be able to fix a module for you if you can't get it done locally. Let me know.

[myorgan]

John,

Thank you for the long response. I didn't find much heat sink compound under the module, but all the screws were there. Needless to say, I'm cautious about the amplifier and module now that this issue has occurred. It has obviously been worked on before. I bought some screws to fill in for the missing ones--both to hold the amplifier assembly down, and to hold the cage/case on. At this point, I'm thinking I'll use the AM-100 until I can get the ADC professionally repaired. The last one I had repaired took 5 months, so I hope it isn't as long this time.

Oh, well. It was worth a try.:o

Michael

[myorgan]

Another Update:

Now that Summer performances have died down a bit, I spent some time with the amplifiers and the organ today. First the simple....

As I was checking the amplifier, I found out a couple of Pedal reed switches were blown. I went from most invasive to least invasive, and even though the switches click when I use the magnet, no sound is produced. I used a 22ga. wire to short the connections, and the circuit worked fine--so I think perhaps the glass is cracked--not sure how that happened just sitting there, but it may be temperature-related. I had a couple of spare reed switches, but someone moved them and was asking me what I lost this time!X-(

Now for the complex...

I had tried using a 9v battery to trip the mute relay, but that didn't work on the bench. The only way was to test it in the organ.

I used one of the AM-100 modules in the triple amp, and this time, the amplifier didn't trip the breaker. Instead--nothing! In desperation, I got a spare Allen RCA M/M cable and went directly from the cage to the amplifier, and nothing. I even turned up the gain to no avail. I'm thinking now that something between the module and the controls has gone bad, or been short-circuited.

Time to have it professionally worked on. I need it in about a month for a performance, so I can't lose any more time farting around with it. Thanks to everyone for their help so far. I've reached the end of my abilities (mostly time).

Thanks again, everyone.

Michael

[toodles]

... I didn't find much heat sink compound under the module...

The purpose of the heat sink compound is to replace the air in the microscopic space between the heat sink and the electronic module (be it a module, power transistor, etc.). The compound is a poor conductor of heat but air is a really poor conductor, so it helps. There should always be a minimum amount of compound when it is used--just a thin smear. Most of it squeezes out when the device is mounted--clean up the excess around whatever it is that was mounted after it is screwed into place.

[jbird604]

Michael,

Since the organ is so mission-critical, if I were you I'd get my hands on one or more standard-issue commercial amplifiers to use in a pinch. Since ADC organs operate with ordinary line level signals going into the amps, you can always pull the RCA input cable off a non-working ADC amp and send that signal into a standard generic amp, then connect your speaker wire to the output of that amp instead of where you usually hook it up.

Here is a link to the Behringer I-Nuke amp that I have used. A couple years ago, I replaced the entire set (17 channels) of ADC amps in an enormous MDS-85 with these amps. They are dirt cheap -- about $150 each for a two-channel unit that can theoretically output 500 watts per channel! That makes it seem a shame to pay Allen Organ Co several hundred dollars for just one 100 watt amp, which is about the way it is when you start trying to replace all the amps in one of their large organs!

This Behringer amp is "self-muting" in that it takes a few seconds to power up when AC is turned on, so you don't have to fool with the muting voltage mess on the ADC assemblies. Just run your audio into the amp (it has 1/4" inputs, so you need those little 50 cent adapters to change RCA plugs to 1/4) and the speaker outputs are "Speak-On" type, so you have to get the proper connector for that too. But it only takes a few minutes to hook up one of these to your organ, and you are up and running.

The downside is that the amp may not fit inside the Allen console without some remodeling, but you can sure have your organ ready to play in a flash when the timing means everything. If the amp has to sit in the floor behind the console, then so be it. At least you will have music!

http://www.mcmelectronics.com/produc...000-/555-13650

[myorgan]

Well, it's been a while since I posted. I just went to get the amplifier today. Needless to say, the repair was quite pricey, but now it works! Evidently, the two center resistors(?--I can't remember the proper name right now) of the four on the back of the module failed, and their resistance was nearly double the other two. I learned they need to be replaced in pairs, and that the pair should be a matched set.

Also during the conversation today, we talked about the line level Allen uses on the ADC amplifiers. I mentioned how I've been requested several times to hook the house sound system to the amplifiers, but I always refuse--saying the connection would put an undue load on the amplifiers and could blow them. My repair guy agreed wholeheartedly.

Evidently, he worked on an MADC organ where they had placed Y-splitters on the output, and ran the other half into a mixer for the church's sound system. They kept complaining about the sound and how it sounded flat (not in pitch, but not a live sound), as well as distorted. My guy pulled the y-splitters off so only the organ's speakers were working, and asked the sound guy if it was better? No distortion, the sound was live again, and the sound was what they had been looking for all along. The organ had been undersized for the church.

Bottom line, the church finally realized the extra load they'd been placing on the amplifier--the sound guy had never worked with a stepping amplifier before, and worked out another way for the organ to fill the space with the organ's amplification system.

We ran out of time to get the amplifier completely connected to the organ--I have a couple of pedal reed switches to replace before I try out everything. Someone was helping me connect the pedals and rammed the corner of the pedals into the reed switch assembly and evidently cracked 2-3. Life is never dull in my world!:o

Michael

[toodles]

One of my Allen dealer friends advises me that the ADC amp is no longer supported by Allen for repair--their support is replacement with an M series amp, at about $2,000.

So if you got your ADC amp repaired at any reasonable price, consider yourself lucky!

[myorgan]

So if you got your ADC amp repaired at any reasonable price, consider yourself lucky!

I do! Wait a minute--this isn't a wedding.:o