Hi everyone,
Bought this as a non runner, the protection relay was welded on so I replaced that and powered using DBT.
Outputs appear to ok with no DC on outputs, everything works fine when I use the heaphone socket but as soon as a disconnect it shorts the 4148 zener in the protection circuit D519 and DBT burns bright. I cant fathom why as headphone out works fine. There is no speaker load connected, I have checked all transistors and they seem fine albeit in circuit.
The only clue I can find is that when measuring the centre pin on the emitter resistors ref ground, one channel reads 2.7k which is what I would expect given the 2.7k in the feedback? The other channel reads 0.80k but goes to 2.7k when headphones plugged in which i dont quite understand as there should be 2.7k still. I have checked the resistors and the 47k caps and all seem ok.
I have checked headphone switch and joints which are all ok. The emitter resistors all read ok, no burned resistors and elco caps are all good. I have checked for dry joints etc.
Been at this for days and cant find a way forward. Urgh
Bought this as a non runner, the protection relay was welded on so I replaced that and powered using DBT.
Outputs appear to ok with no DC on outputs, everything works fine when I use the heaphone socket but as soon as a disconnect it shorts the 4148 zener in the protection circuit D519 and DBT burns bright. I cant fathom why as headphone out works fine. There is no speaker load connected, I have checked all transistors and they seem fine albeit in circuit.
The only clue I can find is that when measuring the centre pin on the emitter resistors ref ground, one channel reads 2.7k which is what I would expect given the 2.7k in the feedback? The other channel reads 0.80k but goes to 2.7k when headphones plugged in which i dont quite understand as there should be 2.7k still. I have checked the resistors and the 47k caps and all seem ok.
I have checked headphone switch and joints which are all ok. The emitter resistors all read ok, no burned resistors and elco caps are all good. I have checked for dry joints etc.
Been at this for days and cant find a way forward. Urgh
All 2.7k and 47pf measure fine and all traces checked ok. When I measure from relay to centre pin on emitter resistors I still get same readings with one channel different to the other unless I plug headphones in. Bizarre, only thing I can think of is that there is something wrong inside new relay?
in the schematic
on page 10/18,
you can find the RL-2 specification.
RL-1, the speaker protection relay, has the similar design.
I am using this to explain the usage of RL-1,
though pin assignments are not the same, just to illustrate the schematic.
page 10, RL-2, study its internal circuit.
when idle
pin 1 and pin16 , the coil connections,
pin 13 is assigned to one channel, connect to the emitter resistors of the output transistors,
pin 13 and pin 11 are connected internally by default.
pin 11 is assign to the headphone jack with a resister 330r in between.
when the relay is activated with current flow through pin 1 and pin16 (coil)
pin 13, the arm will swing from pin 11 to pin 9,
pin 13 will connect to pin 9, (pin 9 connects to speaker circuitry.)
that means when IDLE, pin 13 connects to pin 11 internally,
when activated, pin 13 will connect to pin 9.
here's other channel, same but different pin assignment.
when idle
pin 1 and pin16 , the coil connections,
pin 4 is assigned to another channel, connect to the emitter resistors of the output transistors,
pin 4 and pin 6 are connected internally by default.
pin 6 is assign to the headphone with a resister 330r in between.
when the relay is activated with current flow through pin 1 and pin16 (coil)
pin 4, the arm will swing from pin 6 to pin 8,
pin 4 will connect to pin 8, (pin 8 connects to speaker circuitry.)
that means when IDLE, pin 4 connects to pin 6 internally,
when Activated, pin 4 will connect to pin 8.
when the amp is power on
when a headphone is plug in the phone jack,
it will de-activate the relay...
*******
In the schematic, RL-1,
pin 11 and pin 9, each has a 2k7r used to feed back ac signal to the input diff. stage (-)with a 100r to the ground..
also
pin 6 and pin 8, each has a 2k7r used to feed back ac signal to the input diff. stage (-)with a 100r to the ground..
at the joints of the 0.22r, a 1Mr connects to the (-) feedback pin of the IC,
when measure from the joints of the 0.22r to ground, through the relay contacts,
the value should be 2.7k + 100 ohm.
*******
if you couldn't measure the 2.7k at the center of output resisters ref to ground.
you need to activate the relay to measure the speaker side, or plug in headphone to measure the headphone side,
or power off to measure the headphone side.
if not the relay contacts is not conductive(dirty).
or there are bad joints around.
on page 10/18,
you can find the RL-2 specification.
RL-1, the speaker protection relay, has the similar design.
I am using this to explain the usage of RL-1,
though pin assignments are not the same, just to illustrate the schematic.
page 10, RL-2, study its internal circuit.
when idle
pin 1 and pin16 , the coil connections,
pin 13 is assigned to one channel, connect to the emitter resistors of the output transistors,
pin 13 and pin 11 are connected internally by default.
pin 11 is assign to the headphone jack with a resister 330r in between.
when the relay is activated with current flow through pin 1 and pin16 (coil)
pin 13, the arm will swing from pin 11 to pin 9,
pin 13 will connect to pin 9, (pin 9 connects to speaker circuitry.)
that means when IDLE, pin 13 connects to pin 11 internally,
when activated, pin 13 will connect to pin 9.
here's other channel, same but different pin assignment.
when idle
pin 1 and pin16 , the coil connections,
pin 4 is assigned to another channel, connect to the emitter resistors of the output transistors,
pin 4 and pin 6 are connected internally by default.
pin 6 is assign to the headphone with a resister 330r in between.
when the relay is activated with current flow through pin 1 and pin16 (coil)
pin 4, the arm will swing from pin 6 to pin 8,
pin 4 will connect to pin 8, (pin 8 connects to speaker circuitry.)
that means when IDLE, pin 4 connects to pin 6 internally,
when Activated, pin 4 will connect to pin 8.
when the amp is power on
when a headphone is plug in the phone jack,
it will de-activate the relay...
*******
In the schematic, RL-1,
pin 11 and pin 9, each has a 2k7r used to feed back ac signal to the input diff. stage (-)with a 100r to the ground..
also
pin 6 and pin 8, each has a 2k7r used to feed back ac signal to the input diff. stage (-)with a 100r to the ground..
at the joints of the 0.22r, a 1Mr connects to the (-) feedback pin of the IC,
when measure from the joints of the 0.22r to ground, through the relay contacts,
the value should be 2.7k + 100 ohm.
*******
if you couldn't measure the 2.7k at the center of output resisters ref to ground.
you need to activate the relay to measure the speaker side, or plug in headphone to measure the headphone side,
or power off to measure the headphone side.
if not the relay contacts is not conductive(dirty).
or there are bad joints around.
Last edited:
Which suggests you have approx 1.2K in parallel to the 2.7K . Without any power on the amp what resistance reading do you see measuring from the outputs to ground .
In the schematic, RL-1,
pin 11 and pin 9, each has a 2k7r used to feed back ac signal to the input diff. stage (-)with a 100r to the ground..
also
pin 6 and pin 8, each has a 2k7r used to feed back ac signal to the input diff. stage (-)with a 100r to the ground..
at the joints of the 0.22r, a 1Mr connects to the (-) feedback pin of the IC,
when measure from the joints of the 0.22r to ground, through the relay contacts,
the value should be 2.7k + 100 ohm.
*******
if you couldn't measure the 2.7k at the center of output resisters ref to ground.
you need to activate the relay to measure the speaker side, or plug in headphone to measure the headphone side,
or power off to measure the headphone side.
if not the relay contacts is not conductive(dirty).
or there are bad joints around.
pin 11 and pin 9, each has a 2k7r used to feed back ac signal to the input diff. stage (-)with a 100r to the ground..
also
pin 6 and pin 8, each has a 2k7r used to feed back ac signal to the input diff. stage (-)with a 100r to the ground..
at the joints of the 0.22r, a 1Mr connects to the (-) feedback pin of the IC,
when measure from the joints of the 0.22r to ground, through the relay contacts,
the value should be 2.7k + 100 ohm.
*******
if you couldn't measure the 2.7k at the center of output resisters ref to ground.
you need to activate the relay to measure the speaker side, or plug in headphone to measure the headphone side,
or power off to measure the headphone side.
if not the relay contacts is not conductive(dirty).
or there are bad joints around.
Its clear
though a bit strange, the feedback signal is via the output protection relay to get,
but this will get the feedback signal directly from the speaker circuitry without going through the relay. less distortion may be...
suggest to clean the contacts inside that relay,
and look for bad joints round the relay and that 2.7k resistors.
though a bit strange, the feedback signal is via the output protection relay to get,
but this will get the feedback signal directly from the speaker circuitry without going through the relay. less distortion may be...
suggest to clean the contacts inside that relay,
and look for bad joints round the relay and that 2.7k resistors.
Apologies for the delay in responding to your suggestions.
After some head scratching and testing, I have cured the fault, a slight short between relay coil pins due to some dodgy soldering... cough
However, relay won't change over. No dc on outputs at relay terminals but I only see 10v on the cap for the relay coil circuit. I'm using a 100w dbt and curious as to whether the idle current is pulling the rails down whilst using the dbt? I'm getting 44mv on one channel and 22mv on the other. This uses fixed resistors for bias current so bit of a faff to change. The bias resistors are different between the 2 channels and are parelled so the diff is to be expected. I guess what I'm asking is the bias current causing the rails to drop to prevent the relay from getting the 12v it needs or do I have something else pulling them down?
After some head scratching and testing, I have cured the fault, a slight short between relay coil pins due to some dodgy soldering... cough
However, relay won't change over. No dc on outputs at relay terminals but I only see 10v on the cap for the relay coil circuit. I'm using a 100w dbt and curious as to whether the idle current is pulling the rails down whilst using the dbt? I'm getting 44mv on one channel and 22mv on the other. This uses fixed resistors for bias current so bit of a faff to change. The bias resistors are different between the 2 channels and are parelled so the diff is to be expected. I guess what I'm asking is the bias current causing the rails to drop to prevent the relay from getting the 12v it needs or do I have something else pulling them down?
So all the voltages are correct according to the schematic, right.
connection 601 and 609 connect to the secondary winding of the transformer,
so the resistance is low. but
if you use AC v range of DVM, when power on, you can measure around 31v AC there.
to check the rectifier, use diode range to check the forward and reverse of the individual diode.
if not sure, you can always lift up one end of it to measure. of course de-solder first.
the dc offset is control by IC 401, IC402,
the dc offset is automatically adjust by it.
check the conditions of the power supply of the ICs
and check around the ICs if anything abnormal.
connection 601 and 609 connect to the secondary winding of the transformer,
so the resistance is low. but
if you use AC v range of DVM, when power on, you can measure around 31v AC there.
to check the rectifier, use diode range to check the forward and reverse of the individual diode.
if not sure, you can always lift up one end of it to measure. of course de-solder first.
the dc offset is control by IC 401, IC402,
the dc offset is automatically adjust by it.
check the conditions of the power supply of the ICs
and check around the ICs if anything abnormal.