With D1 out if the circuit it should measure just like a regular diode except in the forward biased direction it will be lower. Reversed biased will be open, infinity, etc. and the forward biased it will be maybe a fifth of a regular diode. For instance a regular diode on my meter reads approx. .500 and a Schottky reads .070. Though D1 looks pretty well isolated in circuit pull it to make sure the circuit isn't messing with your head.
Craig
Craig
Hi,
Compare the reading with D10. They are the same type of diode. Does you meter have diode check? Normally should read with the negative lead in the cathode and the positive lead in the anode about .5 ohms and when leads are reverse should read open.
Compare the reading with D10. They are the same type of diode. Does you meter have diode check? Normally should read with the negative lead in the cathode and the positive lead in the anode about .5 ohms and when leads are reverse should read open.
Hi tauro0221,
My meters have diode check but they measure voltage drop not resistance. And if I measure resistance as you mention I get around 800 ohms with one meter and about 1K ohms with another one, reverse it reads open.
It reads .197 volts and infinity when tested reverse biased. It fails the low resistance test though.
Use the diode checker function and it will give you the voltage drop of the PN junction. My reads .500 which is 1/2 a volt for a normal diode and .070 for the Schottky. I don't know what it will read in the resistance mode, I would imagine it depends on the meter. Check a regular diode and if it reads .500 or so we'll know we're all in the same ballpark.
Craig
Craig
Where did D10 come from? D10 on the 400IV schematic is a plain old signal diode, 1N4148. Don't use that as an example!!!!!
Craig
Craig
Hi Craig,
Yes, a normal diode (1n4007) reads about .5-.6 volts, and this particular Schottky (D1) reads .197 volts out of the circuit.
Hi,
Guys are we talking D1 in the B400 or D1 on the B150. If it is 400 then D1 is zener diode and it is B150 it is a switching diode.
Guys are we talking D1 in the B400 or D1 on the B150. If it is 400 then D1 is zener diode and it is B150 it is a switching diode.
That's probably OK, I measured a 1N5823 out of an old Ampzilla I'm rebuilding. Let me pull my RB400III off the shelf and measure it.
Craig
Craig
Well, the III doesn't use a Schottky or any diode in that position, I tried. No Schottkys at all in the III.
Craig
Craig
D1 IS a Schottky, the cathode indicator is squared off (90 degrees) whereas a zener is angled (45 degrees).
Craig
Craig
HI,
I have a suggestion to the group. Right now since the amplifier goes into protected mode means the preamp is disable making the voltage reading meaningless. So my suggestions is to ground the LM555 pin 3 to disable it. By doing so we are going to make the preamp operational and allow it to read the voltages and compare them against the voltage shown in the schematic. But the output transistor must be remove before doing the test. This will allow to read the voltage feeding the output transistors. We can read the voltage going to the base of the output transistor. Please provide any concern to the suggestion.
I have a suggestion to the group. Right now since the amplifier goes into protected mode means the preamp is disable making the voltage reading meaningless. So my suggestions is to ground the LM555 pin 3 to disable it. By doing so we are going to make the preamp operational and allow it to read the voltages and compare them against the voltage shown in the schematic. But the output transistor must be remove before doing the test. This will allow to read the voltage feeding the output transistors. We can read the voltage going to the base of the output transistor. Please provide any concern to the suggestion.
Hi,
Another idea is used the light bulb in the AC input to power up the amplifier. It will allow to use my suggestion by protecting the amplifier in case of a problem that we are not predicting.
Another idea is used the light bulb in the AC input to power up the amplifier. It will allow to use my suggestion by protecting the amplifier in case of a problem that we are not predicting.
Hey guys,
I think we are getting ahead of ourselves.In otherwards we are
confusing ourselves.😀 First let us get back to basics,we should understand
how this amp circuit work.
1. The protection circuit Q11,Q2 and 555 timer merely mutes the
preamp when there is a fault so no power is cut off, at least for the driver
and outputs.
2. Now this is important,for the protection circuit to work as designed
it is assumed that the bias voltage is at the correct level measured
across two resistors R46 and R52 (0.1 ohm).Which is 10mV.
3. So before we go off on a wild goose chase,we have to check if there
is 10mV across R52,R46.First measure what this bias voltage is currently
at now.😉
If bias is not at 10mV ,the instructions on the schematic says
to power off. Then adjust R19 to full counter-clockwise
position. Turn on power and wait 5 secs. for turn on delay.Turn R21😱
to clockwise until voltage across J4 reads 10mV DC. ( when clearly there is
no R21 in the bias circuit.Forgot to revise or is it a typo error?).
So let's see if we have the correct bias at 10mV first Ok? singa
I think we are getting ahead of ourselves.In otherwards we are
confusing ourselves.😀 First let us get back to basics,we should understand
how this amp circuit work.
1. The protection circuit Q11,Q2 and 555 timer merely mutes the
preamp when there is a fault so no power is cut off, at least for the driver
and outputs.
2. Now this is important,for the protection circuit to work as designed
it is assumed that the bias voltage is at the correct level measured
across two resistors R46 and R52 (0.1 ohm).Which is 10mV.
3. So before we go off on a wild goose chase,we have to check if there
is 10mV across R52,R46.First measure what this bias voltage is currently
at now.😉
If bias is not at 10mV ,the instructions on the schematic says
to power off. Then adjust R19 to full counter-clockwise
position. Turn on power and wait 5 secs. for turn on delay.Turn R21😱
to clockwise until voltage across J4 reads 10mV DC. ( when clearly there is
no R21 in the bias circuit.Forgot to revise or is it a typo error?).
So let's see if we have the correct bias at 10mV first Ok? singa
Hi Singa,
1. If the mute circuit only turns off the preamp then why are the outputs not fried during the 4 second (protect mode) interval? I did a test defeating the mute circuit, turned the amp on and the fuse blew almost instantly, that's how Q24 got fried but not the drivers nor other output transistors, R45 was not fried again, just Q24...
All rail voltages are constant during both modes (protect and power on) +/- 60V, +/- 35V and +/-16V, however, during the very short interval of power on rail voltages drop a little bit because of the problem that occurs somewhere in the amp which indicates a high current demand.
2. I cannot measure bias voltage since the whole power amp is turned off at protect mode (4 seconds), this was confirmed with the destructive test I mentioned. Rail voltages are not cutoff.
3. That turn on delay is precisely the protect mode, after that the power amp is turned on briefly (instead of remaining on) since a fault occurs and then protect mode is triggered so at the present there is no way to set the bias.
I think they refer to R19 which is the bias pot...
Hi frikecello,
Your description of the mute defeat leaves me puzzled,
I think I will look at the circuit again and see if I can figure it out or not.
In the mean time I hope the others have better ideas. You have
helped us by your "tests" thank you for your patience.🙂 singa
Your description of the mute defeat leaves me puzzled,
I think I will look at the circuit again and see if I can figure it out or not.
In the mean time I hope the others have better ideas. You have
helped us by your "tests" thank you for your patience.🙂 singa
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