I purchased another Adcom, but this one appears to have a problem in the fan circuit.
Normally, at start-up, the voltage to the fan is approx. 4 volts.
On this one, it's only 2.86 which isn't enough to make the fan start turning.
With the wires to the fan cut (fan disconnected), we have about 12 volts by the way.
On other Adcoms of mine, we replaced the 220 ohm 1/4 watt resistor R336 by a 500 ohm multi-turn pot, which enables us to control fan speed.
Since voltage was low on this one, we replaced it by a same pot to see whether we could increase voltage by decreasing resistance.
The strange thing is that when turning the pot one way, the voltage increased only a little, but instead of keeping increasing the whole time, it would decrease sometimes while still turning the same way, then increase again !
Then, suddenly, with the voltage still too low to jumpstart the fan, suddenly while turning the pot the voltage would jump right from 4 volts to over 12 volts (I think the same voltage as the power supply voltage feeding the amp, could be wrong though) instead of increasing gradually, and the fan would start turning. Then, when turning back the other way, it would not decrease a lot until it would suddenly drop back to below 3 volts and the fan would stop turning.
Any idea ? I can provide the schematics if anyone wants to have a look.
Normally, at start-up, the voltage to the fan is approx. 4 volts.
On this one, it's only 2.86 which isn't enough to make the fan start turning.
With the wires to the fan cut (fan disconnected), we have about 12 volts by the way.
On other Adcoms of mine, we replaced the 220 ohm 1/4 watt resistor R336 by a 500 ohm multi-turn pot, which enables us to control fan speed.
Since voltage was low on this one, we replaced it by a same pot to see whether we could increase voltage by decreasing resistance.
The strange thing is that when turning the pot one way, the voltage increased only a little, but instead of keeping increasing the whole time, it would decrease sometimes while still turning the same way, then increase again !
Then, suddenly, with the voltage still too low to jumpstart the fan, suddenly while turning the pot the voltage would jump right from 4 volts to over 12 volts (I think the same voltage as the power supply voltage feeding the amp, could be wrong though) instead of increasing gradually, and the fan would start turning. Then, when turning back the other way, it would not decrease a lot until it would suddenly drop back to below 3 volts and the fan would stop turning.
Any idea ? I can provide the schematics if anyone wants to have a look.
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When the fan is disconnected (wires to the fan cut) we measured over 12 volts on the wires that normally go to the fan.
When the fan is connected, we measured 2.86 volt on the same wires, which is too low.
In both cases the voltage is constant.
We also tried with an identical fan from another GFA-4402.
Yes the probes were directly on the wires to the fan.
When the fan is connected, we measured 2.86 volt on the same wires, which is too low.
In both cases the voltage is constant.
We also tried with an identical fan from another GFA-4402.
Yes the probes were directly on the wires to the fan.
We measured with the negative probe to ground.
Without the fan connected, there is the same voltage (+12V) as the power supply, which is normal as the positive wire to the fan seems to be coming straight from the +12V, it's the negative wire that has all the circuitry on it.
We measured a voltage drop of 9 volts, so there was only 3 volts left which is not enough to start the fan. On the other amps there is 4 volts which does start the fans.
We think TIP61 might be faulty, or thermistor R337. Both are not very common parts.
We'll try and repair the circuit. If we can't we'll bypass it and make our own circuit with a relay hooked up to the +12V, gnd and remote terminals and a 1 watt resistor or 1 / 1.25 watt potentiometer in series with the fan.
We experimented a bit with some resistors, we need approx 120 ohms. Two 1/4 watt 200 ohm resistors in parallel got a little warm, so 1 watt should be better. A 200 ohm 1.25 watt potentiometer might be best.
But I will try and get the TIP61 or an alternative and maybe the thermistor if I can and see whether that's the problem. Uncommon parts are a bit harder to get over here.
If we can't find them, we'll bypass the circuit.
By the way, when I purchased the amp the circuit was already bypassed by a similar idea , but it was very clumsily done so I removed it.
Without the fan connected, there is the same voltage (+12V) as the power supply, which is normal as the positive wire to the fan seems to be coming straight from the +12V, it's the negative wire that has all the circuitry on it.
We measured a voltage drop of 9 volts, so there was only 3 volts left which is not enough to start the fan. On the other amps there is 4 volts which does start the fans.
We think TIP61 might be faulty, or thermistor R337. Both are not very common parts.
We'll try and repair the circuit. If we can't we'll bypass it and make our own circuit with a relay hooked up to the +12V, gnd and remote terminals and a 1 watt resistor or 1 / 1.25 watt potentiometer in series with the fan.
We experimented a bit with some resistors, we need approx 120 ohms. Two 1/4 watt 200 ohm resistors in parallel got a little warm, so 1 watt should be better. A 200 ohm 1.25 watt potentiometer might be best.
But I will try and get the TIP61 or an alternative and maybe the thermistor if I can and see whether that's the problem. Uncommon parts are a bit harder to get over here.
If we can't find them, we'll bypass the circuit.
By the way, when I purchased the amp the circuit was already bypassed by a similar idea , but it was very clumsily done so I removed it.
By the way, when looking at the schematics, the positive wire to the fan seems te be connected to something called SW RADIO.
My father thinks it's connected straight to the remote. Is this true ??!?! If it is, then it's a very strange design as that would imply the fan would run straight off the remote of the head unit which would be bad if you hook up multiple of these amps to your HU.
In my car that wouldn't be a problem since I use a relay for the remote anyway since I use 6 amplifiers, but not everybody uses a relay.
My father thinks it's connected straight to the remote. Is this true ??!?! If it is, then it's a very strange design as that would imply the fan would run straight off the remote of the head unit which would be bad if you hook up multiple of these amps to your HU.
In my car that wouldn't be a problem since I use a relay for the remote anyway since I use 6 amplifiers, but not everybody uses a relay.
Your schematic is incomplete. Adcom added a small PCB right on top of the turn on lead connection that used two transistors to alter the turn on lead current draw issues the original amp design had. Try looking at any other schematics you might have I am sure it will be in one of them if the schematic is updated.
Originally Adcom had a turn on lead current draw of almost 100ma. This presented issues to HU's so they did a add-on board that was screwed right to the top of the turn on lead edge connector and the trace on the board was cut to allow the add on to work properly. The add-on board required +12 and ground and one out of 12 volt to the amp so its a three wire hook up plus the connection to the turn on lead lug.
If not I will try and find my old schematics and relay the turn on circuit board mod to you....
Originally Adcom had a turn on lead current draw of almost 100ma. This presented issues to HU's so they did a add-on board that was screwed right to the top of the turn on lead edge connector and the trace on the board was cut to allow the add on to work properly. The add-on board required +12 and ground and one out of 12 volt to the amp so its a three wire hook up plus the connection to the turn on lead lug.
If not I will try and find my old schematics and relay the turn on circuit board mod to you....
Thanks Perry, I'll get it today.
Cecil, we were not able to locate that extra PCB you mentioned.
Could it be our amplifiers don't have it, or are we missing something ?
What we could do is put our multimeter in series with the remote wire that goes from the power supply to the amplifier's remote terminal, and measure current. If the fans are directly on the remote turn on, then there should be over 100 mA as the fans are 0.25A and they are supplied approx 4 volt by the amplifier's fan circuit.
Cecil, we were not able to locate that extra PCB you mentioned.
Could it be our amplifiers don't have it, or are we missing something ?
What we could do is put our multimeter in series with the remote wire that goes from the power supply to the amplifier's remote terminal, and measure current. If the fans are directly on the remote turn on, then there should be over 100 mA as the fans are 0.25A and they are supplied approx 4 volt by the amplifier's fan circuit.
Sounds like your Adcom's are not modded with the turn on boards. I will try to find the schematic and mail it to you. It was a common problem and a simple mod is to use a Bosch turn on relay that is not current limited. This may be part of the fan problem and it may not. I will direct mail you about this...C
Our amps don't seem to have this extra circuitry.
I will swap TIP61, if that doesn't fix the problem then I'll bypass the fan's circuitry and use a relay to start the fan as soon as the amplifier gets the 'go' from the head-unit.
It won't be temperature controlled so I'll have it run a little faster than they normally do on these amps, just in case.
Also, I will build am external relay for the person who will be buying 4 Adcoms from me, don't want 4 fans to be running of his head-unit's remote wire, he'd be looking at approx 400 mA, it could damage his HU.
The fans on the other amps run fine so no need to do anything about them, I am just reducing R336 a little bit so they run a tiny bit faster so I am sure they start up. As you said older fans can be harder to start spinning, increasing the voltage a little bit avoids problems, keeps the amp cooler and they are still pretty silent.
So I need to find two relays, one for inside the malfunctioning amp and one for outside for the 4 amps. Are there 'quiet' relays ? I don't want them to make clicking sounds as this person might do SQ competitions, I don't know. I personally like the clicking sound of my relay in my car when I power on the HU, but I don't do SQ competitions. I think they take off points for clicking sounds.
I will swap TIP61, if that doesn't fix the problem then I'll bypass the fan's circuitry and use a relay to start the fan as soon as the amplifier gets the 'go' from the head-unit.
It won't be temperature controlled so I'll have it run a little faster than they normally do on these amps, just in case.
Also, I will build am external relay for the person who will be buying 4 Adcoms from me, don't want 4 fans to be running of his head-unit's remote wire, he'd be looking at approx 400 mA, it could damage his HU.
The fans on the other amps run fine so no need to do anything about them, I am just reducing R336 a little bit so they run a tiny bit faster so I am sure they start up. As you said older fans can be harder to start spinning, increasing the voltage a little bit avoids problems, keeps the amp cooler and they are still pretty silent.
So I need to find two relays, one for inside the malfunctioning amp and one for outside for the 4 amps. Are there 'quiet' relays ? I don't want them to make clicking sounds as this person might do SQ competitions, I don't know. I personally like the clicking sound of my relay in my car when I power on the HU, but I don't do SQ competitions. I think they take off points for clicking sounds.
I have and use a PG Tidd10 to control all turn on's and turn off's and time delays and what not for all my gear after the HU. If you have ever seen one, you will see why I use it. It does everything you could ever want to do to control all your gear off your HU.
Unfortunately they don't make them anymore and have not for more then three years now. Google search the model number and you should be able to see some lit about it. Tidd10 and Tidd5
Each output is fused, LED indicated, Delayed or instant on, or delay or instant turn off. Variable timers on all outputs etc... Its a great way to kill turn on and turn off thump in un-muted systems of past designs. I was lucky enough to grab one of the last ones PG had in stock when they stopped making and selling them just after the Xenon line stopped.
The two transistor turn on circuit for the Adcom is a easy build on breadboard. No rare or un-available parts and what not. It is so small it was screwed right on top of the lug for the turn on signal inside the amp. If you need to do a quick fix I suggest a simple Bosch relay with its coil activated by the HU, and its output being fused properly to all your external gear, Cheap, simple, and it works forever. If turn on clicking is a worry wrap it in soft foam insulation, and or mount it in the trunk of the ride.... I used this same setup years before I purchased a Tidd10....
Unfortunately they don't make them anymore and have not for more then three years now. Google search the model number and you should be able to see some lit about it. Tidd10 and Tidd5
Each output is fused, LED indicated, Delayed or instant on, or delay or instant turn off. Variable timers on all outputs etc... Its a great way to kill turn on and turn off thump in un-muted systems of past designs. I was lucky enough to grab one of the last ones PG had in stock when they stopped making and selling them just after the Xenon line stopped.
The two transistor turn on circuit for the Adcom is a easy build on breadboard. No rare or un-available parts and what not. It is so small it was screwed right on top of the lug for the turn on signal inside the amp. If you need to do a quick fix I suggest a simple Bosch relay with its coil activated by the HU, and its output being fused properly to all your external gear, Cheap, simple, and it works forever. If turn on clicking is a worry wrap it in soft foam insulation, and or mount it in the trunk of the ride.... I used this same setup years before I purchased a Tidd10....
Oh by your last post I am sure there is something pulling the 12 down by 9 volts this is not the way it was meant to work. There is some defective component in the power supply and fan circuitry causing this issue, of this I am sure...Let me know what you find broken as its a first for my files...thanks ...
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