I understand. I didn't know if it would effect or alter the tests. I am going to use the 200w bulb.
I have tried the 200 watt bulb before and the oscillations were still there.
Steve Thanks again will let you know in a few days what I have.
I understand. I didn't know if it would effect or alter the tests. I am going to use the 200w bulb.
I have tried the 200 watt bulb before and the oscillations were still there.
Steve Thanks again will let you know in a few days what I have.
The power supply seems to be fine.
I made some checks on the amplifier boards still nothing.
I connected a 15 ohm load across the speaker terminals and unit operated fairly normal. I can take the volume up to 3/4 level and then relays will come in and out but if you decrease volume just a little the relays will remain on with out cycling.
Steve, you mentioned awhile back about checking the amperage on the outputs. I didn't do it because I did not know how. I think I need to do this. Can you give me any directions? I have the data sheets on the outputs, but don't know what I am looking for.
I think I know that increasing the ohm load will decrease the amperage on the outputs.
I connected a spec 1 preamp output to the marantz amp in jacks and the marantz relays cycled when the volume of the spec1 was increased. I also connected the preamp outs of the marantz to a spec2 amp and maranz operated fine.
I made some checks on the amplifier boards still nothing.
I connected a 15 ohm load across the speaker terminals and unit operated fairly normal. I can take the volume up to 3/4 level and then relays will come in and out but if you decrease volume just a little the relays will remain on with out cycling.
Steve, you mentioned awhile back about checking the amperage on the outputs. I didn't do it because I did not know how. I think I need to do this. Can you give me any directions? I have the data sheets on the outputs, but don't know what I am looking for.
I think I know that increasing the ohm load will decrease the amperage on the outputs.
I connected a spec 1 preamp output to the marantz amp in jacks and the marantz relays cycled when the volume of the spec1 was increased. I also connected the preamp outs of the marantz to a spec2 amp and maranz operated fine.
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I would suggest placing a 10 ohm resistor in series with the collectors of the output transistors.
This will allow you to easily measure the current, will provide an indication of excessive current (smoke) and go a substantial way toward protecting the transistors.
With no input, only a very small current should flow through the output transistors in any case.
Measuring the voltage drop across these resistors (via your scope possibly) will give you a direct indication of collector current.
This will allow you to easily measure the current, will provide an indication of excessive current (smoke) and go a substantial way toward protecting the transistors.
With no input, only a very small current should flow through the output transistors in any case.
Measuring the voltage drop across these resistors (via your scope possibly) will give you a direct indication of collector current.
Evening Steve,
I will install resistors as you suggest.
The outputs are not in a friendly location, Can I install a resistor on each rail that feed the collectors of the outputs?
I understand I would not get each outputs amperage draw.
I was thinking, which is dangerous, but this unit draws 450watts at full power. I can run the volume up all the way with no signal with no problems in 2 channel mode. I can also run volume up very high in 4 channel mode with a FM signal. I am using a 100 to a 200 watt bulb. The volume will get higher with the 200 watt bulb with no problems. I also have a variac if needed.
I did find a 1000MFD 35V cap that tested at 922mfd. It was attached to the power supply feeding the 400hz oscillator and Dolby processing boards.
Do you think it would be smart to try unit off of the dim bulb at this point?
I will install resistors as you suggest.
The outputs are not in a friendly location, Can I install a resistor on each rail that feed the collectors of the outputs?
I understand I would not get each outputs amperage draw.
I was thinking, which is dangerous, but this unit draws 450watts at full power. I can run the volume up all the way with no signal with no problems in 2 channel mode. I can also run volume up very high in 4 channel mode with a FM signal. I am using a 100 to a 200 watt bulb. The volume will get higher with the 200 watt bulb with no problems. I also have a variac if needed.
I did find a 1000MFD 35V cap that tested at 922mfd. It was attached to the power supply feeding the 400hz oscillator and Dolby processing boards.
Do you think it would be smart to try unit off of the dim bulb at this point?
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As long as the resistors are between the power rail and the collectors, and not between (say) the power supply and the amplifier board itself.
I would recommend no testing with any input right now.
I would want to see you being able to wind the volume all the way up, and down, and at any speed, with nothing much happening.
Just to minimise the risk of picking up noise, I would short the inputs to ground.
That's within spec for an electrolytic capacitor. If you have any reason to be suspicious about it, you could replace it, but I suspect it won't really make any difference to the problem you're having.
With the resistors in series with the output transistors, and with caution, and with a hand close to the power switch, yeah.
I might have not been clear,
There are 4 sets of outputs for left channel and 4 sets of outputs for the right channel.
I only have the right channel in service.
Two rails for the right channel are for 4 outputs, (2 NPN 's & 2 PNP's).
Can I use one resistor for two outputs (1 resistor for 2 NPN transistors and 1 resistor for the 2 PNP transistors)?
Sorry for being confusing I am not very good at communication
There are 4 sets of outputs for left channel and 4 sets of outputs for the right channel.
I only have the right channel in service.
Two rails for the right channel are for 4 outputs, (2 NPN 's & 2 PNP's).
Can I use one resistor for two outputs (1 resistor for 2 NPN transistors and 1 resistor for the 2 PNP transistors)?
Sorry for being confusing I am not very good at communication
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I don't see any reason why not.
No Smoke.
I went a head and disassembled the receiver and install 10 ohm 1/4watt resistors to each collector of each output. I feed amplifier boards with the rails with no resistors.
Grounded CD input jack and placed selector to CD.
Powered up first with dim bulb with no problems. Connected receiver to variac and slowly ramped up to 120VAC with still no problems. Connected DVM across each resistor then used my scope across each resistor. The scope had a straight line trace with pretty close readings to the DVM.
0% volume voltage was stable. 100% volume the voltage on the front channel would rise then fall then rise then fall but it sort of stabilized at the voltage readings on the attachment. The voltage would be at 2.0 then climb to 2.438 the fall to 2.389 then climb to 2.669 the fall to 2.602. I know its minute but I thought I would mention it.
I went a head and disassembled the receiver and install 10 ohm 1/4watt resistors to each collector of each output. I feed amplifier boards with the rails with no resistors.
Grounded CD input jack and placed selector to CD.
Powered up first with dim bulb with no problems. Connected receiver to variac and slowly ramped up to 120VAC with still no problems. Connected DVM across each resistor then used my scope across each resistor. The scope had a straight line trace with pretty close readings to the DVM.
0% volume voltage was stable. 100% volume the voltage on the front channel would rise then fall then rise then fall but it sort of stabilized at the voltage readings on the attachment. The voltage would be at 2.0 then climb to 2.438 the fall to 2.389 then climb to 2.669 the fall to 2.602. I know its minute but I thought I would mention it.
Smoke
The previous test was done with no output load. Got up this morning realizing I did not have dummy load connected.
Connected dummy load and preformed test. Obtained attached readings.
Power down using power switch the wanted to verify reading, Turned on power switch and smoked something on the phase converter board. Don't see anything burnt and voltage is the same as before the smoke.
Should the volts and amperage be pretty close to the same on a PNP and a NPN output transistor?
The previous test was done with no output load. Got up this morning realizing I did not have dummy load connected.
Connected dummy load and preformed test. Obtained attached readings.
Power down using power switch the wanted to verify reading, Turned on power switch and smoked something on the phase converter board. Don't see anything burnt and voltage is the same as before the smoke.
Should the volts and amperage be pretty close to the same on a PNP and a NPN output transistor?
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Yeah, the 10 ohm resistors are there to "smoke" if the output draws significant current.
Without a load it should not draw any significant current, and you've shown that.
This demonstrated (to some likely level of probability) that any fault causing both output transistors to be simultaneously turned on is not (or is no longer) present.
This was my main worry, and it can kill your output transistors very quickly.
Attempting to drive speakers (or a dummy load) will increase the current and overheat the deliberately low wattage resistors.
What you need to do is (without any input <-- this is important) connect your dummy load and measure the voltage across the dummy load (on an AC range whilst turning the volume up and down.
You should see no smoke, and no significant voltage.
edit: it appears that the output stage is biased to draw more current than I might expect (around 100mA?). I believe you have the instructions for setting the biasing. Measure the appropriate voltages and tell me what they are compared whith what they should be. Don't adjust anything yet.
Without a load it should not draw any significant current, and you've shown that.
This demonstrated (to some likely level of probability) that any fault causing both output transistors to be simultaneously turned on is not (or is no longer) present.
This was my main worry, and it can kill your output transistors very quickly.
Attempting to drive speakers (or a dummy load) will increase the current and overheat the deliberately low wattage resistors.
What you need to do is (without any input <-- this is important) connect your dummy load and measure the voltage across the dummy load (on an AC range whilst turning the volume up and down.
You should see no smoke, and no significant voltage.
edit: it appears that the output stage is biased to draw more current than I might expect (around 100mA?). I believe you have the instructions for setting the biasing. Measure the appropriate voltages and tell me what they are compared whith what they should be. Don't adjust anything yet.
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I measured the dummy load voltage as you have requested using my DVM on A/C volts. Recorded readings and attached. I performed it with the cd input jacks grounded, dim bulb in place, resistors still on collectors of outputs.
On the first test at 75% volume one or two of the resistors smoked but did not open the up.
Did fine on the second round. It sometimes will not always do the same thing each time it is powered up.
I have made adjustments to the amplifier boards often, but they seem to not stay set. I do not know which adjustment is for or does what but I have attached the procedure and schematic to make it easier for you.
On the first test at 75% volume one or two of the resistors smoked but did not open the up.
Did fine on the second round. It sometimes will not always do the same thing each time it is powered up.
I have made adjustments to the amplifier boards often, but they seem to not stay set. I do not know which adjustment is for or does what but I have attached the procedure and schematic to make it easier for you.
Attachments
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The volume test tells me that there is still a problem. I suspect that if you removed the resistors and the bulb, you would need to replace the output drivers again.
Try again, but measure DC voltage across the output. A small AC voltage may be indicative of noise, but I suspect it's a DC voltage. Any DC voltage should not exceed some small number of millivolts.
Try again, but measure DC voltage across the output. A small AC voltage may be indicative of noise, but I suspect it's a DC voltage. Any DC voltage should not exceed some small number of millivolts.
I know the other day I asked about trying unit with no protection but my gut was with you that I was going to be replacing outputs again if I did that.
With the DVM on DCV I get a 19 to 23 mv erratic swing with a volume of 0 to 50%.
At 75% I get 18 - 22 mv erratic swing. And at 100% I get a 16mv - 23 mv swing.
No smoke this time around. Why aren't the 1/4 watt resistors failing when smoked?
I placed the scope across the output and get a +20mv to a -20mv sine wave.
With the DVM on DCV I get a 19 to 23 mv erratic swing with a volume of 0 to 50%.
At 75% I get 18 - 22 mv erratic swing. And at 100% I get a 16mv - 23 mv swing.
No smoke this time around. Why aren't the 1/4 watt resistors failing when smoked?
I placed the scope across the output and get a +20mv to a -20mv sine wave.
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They will eventually. They are probably out of spec now -- i.e. their resistance differs from the (once) marked value by something greater than their tolerance.
If something catastrophic happens, they'll probably either buy time or go open circuit before your transistors expire -- or that's the gamble.
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Looking at those results, the right front amplifier seems to have excessive biasing of the output transistors. All of the other amplifiers show a 10 to 20 mA quiescent current.
I would first try adjusting the bias (or attempting to) to get the quiescent current in that range.
The next step is to figure out if there's something else going on (and the smoke suggests there is)
I would first try adjusting the bias (or attempting to) to get the quiescent current in that range.
The next step is to figure out if there's something else going on (and the smoke suggests there is)
Running some checks. I have two transistor checkers one give a hfe number and the other is just a bulb that lights if the transistor is good.
Dumb question. I have one output transistor when checked with my transistor checker I get a 0 hfe. and the other checker gives a no lighted bulb. If I check it with a ohm meter it shows good.
What do I need to believe?
All other transistors show good on all three test.
Dumb question. I have one output transistor when checked with my transistor checker I get a 0 hfe. and the other checker gives a no lighted bulb. If I check it with a ohm meter it shows good.
What do I need to believe?
All other transistors show good on all three test.
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I would replace it, given that it's clearly behaving differently to the other transistors.
It is possible that it is damaged enough that it won't operate as a transistor any more, but the basic diode junctions are not yet destroyed,
It is possible that it is damaged enough that it won't operate as a transistor any more, but the basic diode junctions are not yet destroyed,
