AKAI AA-1200/1175
 

I have an old AA-1200 receiver that works intermittently. When it
cuts out I can detect a relay on the circuit board changing states. I
assume some protection circuit has detected an unsafe condition and
shut it down. My problem is I have no information on the unit. Can
anyone provide advice or steer me to a source of documentation?

AKAI AA-1200/1175
 

On Jun 14, 9:14 pm, wrote:
I have an old AA-1200 receiver that works intermittently. When it
cuts out I can detect a relay on the circuit board changing states. I
assume some protection circuit has detected an unsafe condition and
shut it down. My problem is I have no information on the unit. Can
anyone provide advice or steer me to a source of documentation?

AA-1200, eh? Any evidence of a manufacturer's label?

The relay on the circuit board thinks that there is a steady DC at the
speaker outputs and is disconnecting said speaker outputs from the
amplifier to keep the voice coils from burning out. This can happen
for any number of reasons, including a defective detection circuit.
In my experience, this is not so easy to troubleshoot, especially if
you have to play the thing for a long period to get it to kick out.

Fool with a heat gun/soldering iron. Note that the relay is not the
problem, but the output transistors quite possibly could be. Put a
voltmeter, preferably analog, on the power amplifier output (they run
into that relay) so you can watch what happens to the voltage as the
amplifier is running; possibly you may see a DC voltage developing as
a transistor heats up and unbalances the power amplifier.

M Kinsler

AKAI AA-1200/1175
 

"m kinsler" wrote in message
oups.com...
On Jun 14, 9:14 pm, wrote:
I have an old AA-1200 receiver that works intermittently. When it
cuts out I can detect a relay on the circuit board changing states. I
assume some protection circuit has detected an unsafe condition and
shut it down. My problem is I have no information on the unit. Can
anyone provide advice or steer me to a source of documentation?

AA-1200, eh? Any evidence of a manufacturer's label?

The relay on the circuit board thinks that there is a steady DC at the
speaker outputs and is disconnecting said speaker outputs from the
amplifier to keep the voice coils from burning out. This can happen
for any number of reasons, including a defective detection circuit.
In my experience, this is not so easy to troubleshoot, especially if
you have to play the thing for a long period to get it to kick out.

Fool with a heat gun/soldering iron. Note that the relay is not the
problem, but the output transistors quite possibly could be. Put a
voltmeter, preferably analog, on the power amplifier output (they run
into that relay) so you can watch what happens to the voltage as the
amplifier is running; possibly you may see a DC voltage developing as
a transistor heats up and unbalances the power amplifier.

M Kinsler


The first question is does it do it with no music playing - ie with it just
sitting there idling, do you hear that relay drop out ? If yes, and it drops
back in on its own, problem could be as simple as a bad joint, likely
located in the power amps, possibly in the power supply, remote possibility
of elsewhere.

If no, can you get it to do it on a particular piece of music at a
particular place ie on a heavy bass line ? If yes, problem may be equally
simple - a bad speaker. Disconnect them one at a time, and replay the music
that initiated the cut out.

If problem seems totally random, then most likely cause is still bad joints,
although it could be an intermittent component failure in the output stages
( not too likely if it works ok when it is working ) or a problem with the
actual fault detect / delay circuit. I've had the delay timing cap cause
this sort of thing, for instance. If it does turn out to be a genuine
component fault, electrolytics on an old unit, are prime suspects. If you do
get to the point of deciding that it is just a random intermittent failure,
the next move is to remove the covers, and see if you can provoke the
problem by firm tapping around inside with the butt end of a screwdriver. I
would recommend doing this either without your speakers connected, or with
an old pair on it. If you can make it go off, switch to something lighter
like a Biro pen for the tapping, to try to localise the bad joint area,
before actually looking for it. Most likely places would be around the
output heatsink area, and the power supply section. Could even be a slack
fuseholder. I have also had bad joints on the relay itself, particularly on
the coil pins, on many manufacturers' units. A bad joint there will give the
sort of symptoms you are experiencing.

Arfa

AKAI AA-1200/1175
 

On Jun 15, 12:52 am, m kinsler wrote:
On Jun 14, 9:14 pm, wrote:

I have an old AA-1200 receiver that works intermittently. When it
cuts out I can detect a relay on the circuit board changing states. I
assume some protection circuit has detected an unsafe condition and
shut it down. My problem is I have no information on the unit. Can
anyone provide advice or steer me to a source of documentation?

AA-1200, eh? Any evidence of a manufacturer's label?

The relay on the circuit board thinks that there is a steady DC at the
speaker outputs and is disconnecting said speaker outputs from the
amplifier to keep the voice coils from burning out. This can happen
for any number of reasons, including a defective detection circuit.
In my experience, this is not so easy to troubleshoot, especially if
you have to play the thing for a long period to get it to kick out.

Fool with a heat gun/soldering iron. Note that the relay is not the
problem, but the output transistors quite possibly could be. Put a
voltmeter, preferably analog, on the power amplifier output (they run
into that relay) so you can watch what happens to the voltage as the
amplifier is running; possibly you may see a DC voltage developing as
a transistor heats up and unbalances the power amplifier.

M Kinsler

The AA-1200 is made by Akai. I put that in the title but neglected to
repeat it in the post. Sorry for the confusion. I appreciate the
response and will follow up on your suggestions. I have a scope I get
on the output to check for DC levels. Any Idea how much the balance
needs to be off to kick off the protection circuit?

AKAI AA-1200/1175