Tangerine
Thanks for all the fish!
Hello all.
This thread will be documenting that path to getting my A-9 back up an running.
I bought it a few years ago, it was not running and I assumed an easy repair was needed.
It's remained in storage in a sub-tropical environment in Sth East Queensland, Australia (this fact has weight later in this post).
The repair is being done by an engineer colleague of mine who is a hobbyist with vast experience.
There are no pics as yet, they are coming and will be worth a thousand words.
Current status (as yet power has not been applied to the amplifier):
0. Corrosion of the chassis and shielding covers (remember sub-tropical...?).
1. A prior repair has permanently shorted out the Protection Relay R3, which according to the circuit and manual description drives the main audio output (both channels) to the sub-harmonic Indication circuit, power meter circuit and also drives the Headphone outputs. Quite perplexing as to why this was done, but at this stage I assume the original relay (which is a specialised solid state device) has failed and repair by replacement was not an available option. The relay part number is ASR-027, and was recognised on eBay.
Q1: What is your intent with this type of prior issue?
Two choices:
1. Leave it as is,
2. Fix it to original specification. If you leave as is, there is a risk that if the audio outputs go DC then all the voltage is applied to the three circuits as described earlier. This could be disastrous to the internal circuits as the relay is supposed to remove the signal if a fault is detected. Currently this self protection cannot occur and the amp may have already been subject to this exact scenario.
Ans: 1 is not an option!!
2. The DC voltage regulator has burnt components. The regulator is a simple series regulator that produces +/-60 VDC regulated to the main amplifier board from +/-80 unregulated at about 100ma load. Hence the regulator is about 12 watts total. A prior repair has also been carried out on the regulator, resulting in many of the PCB tracks being built up with solder rather than just copper. I can't see that any of the original components have been replaced, but the failed components now need to be replaced. This would seem to be a common fault at this time. The prior repair has left flux all over the regulator board (a pet hate of mine) since flux can become conductive over time and heat. (reason: prior sloppy workmanship). The painful part is that prior tampering with this board (movement) has stressed the wire-wrap joints to the regulator, some have been soldered and others are unwrapping.
3. There are several dry joints on the main amp board. This is something for your forum: The dry joints are caused by mechanical vibration of the relays, the relays produce a shock every time they open and close (not the solid state relay mentioned in 1.) but the high power relays protecting the driver and speakers. Over time this continuous shock produces dry joints to components with any mass, such as the inductors, relays etc....
Way forward:
1. Take some snaps of the original condition.
2. Repair the regulator and load it off (out of) circuit
3. Turn amp on and check ALL voltages for amplifier.
4. Determine what else is wrong with the amp.
Comment: there is no way this amp functioned in the current condition and as found, my assumption is the amp must have bought it on spec. The reason the amp did not smell on power up is that it had already burnt out and hence couldn't burn much more. Note: No fuses have blown, which means whatever happened thus far has not involved over-current conditions (which is a saving grace).
This thread will be documenting that path to getting my A-9 back up an running.
I bought it a few years ago, it was not running and I assumed an easy repair was needed.
It's remained in storage in a sub-tropical environment in Sth East Queensland, Australia (this fact has weight later in this post).
The repair is being done by an engineer colleague of mine who is a hobbyist with vast experience.
There are no pics as yet, they are coming and will be worth a thousand words.
Current status (as yet power has not been applied to the amplifier):
0. Corrosion of the chassis and shielding covers (remember sub-tropical...?).
1. A prior repair has permanently shorted out the Protection Relay R3, which according to the circuit and manual description drives the main audio output (both channels) to the sub-harmonic Indication circuit, power meter circuit and also drives the Headphone outputs. Quite perplexing as to why this was done, but at this stage I assume the original relay (which is a specialised solid state device) has failed and repair by replacement was not an available option. The relay part number is ASR-027, and was recognised on eBay.
Q1: What is your intent with this type of prior issue?
Two choices:
1. Leave it as is,
2. Fix it to original specification. If you leave as is, there is a risk that if the audio outputs go DC then all the voltage is applied to the three circuits as described earlier. This could be disastrous to the internal circuits as the relay is supposed to remove the signal if a fault is detected. Currently this self protection cannot occur and the amp may have already been subject to this exact scenario.
Ans: 1 is not an option!!
2. The DC voltage regulator has burnt components. The regulator is a simple series regulator that produces +/-60 VDC regulated to the main amplifier board from +/-80 unregulated at about 100ma load. Hence the regulator is about 12 watts total. A prior repair has also been carried out on the regulator, resulting in many of the PCB tracks being built up with solder rather than just copper. I can't see that any of the original components have been replaced, but the failed components now need to be replaced. This would seem to be a common fault at this time. The prior repair has left flux all over the regulator board (a pet hate of mine) since flux can become conductive over time and heat. (reason: prior sloppy workmanship). The painful part is that prior tampering with this board (movement) has stressed the wire-wrap joints to the regulator, some have been soldered and others are unwrapping.
3. There are several dry joints on the main amp board. This is something for your forum: The dry joints are caused by mechanical vibration of the relays, the relays produce a shock every time they open and close (not the solid state relay mentioned in 1.) but the high power relays protecting the driver and speakers. Over time this continuous shock produces dry joints to components with any mass, such as the inductors, relays etc....
Way forward:
1. Take some snaps of the original condition.
2. Repair the regulator and load it off (out of) circuit
3. Turn amp on and check ALL voltages for amplifier.
4. Determine what else is wrong with the amp.
Comment: there is no way this amp functioned in the current condition and as found, my assumption is the amp must have bought it on spec. The reason the amp did not smell on power up is that it had already burnt out and hence couldn't burn much more. Note: No fuses have blown, which means whatever happened thus far has not involved over-current conditions (which is a saving grace).