The output rail is connected to all four emitter resistors.
Clip onto the emitter lead of one output resistor. switch on. Measure the voltage to the output. that gets you the Vre of one device.
Switch off. move the clip on probe to the next device. Repeat until you have all four Vre.
If you have a steady hand and want to accept the risk of blowing up the amplifier by shorting between Collector and Emitter, then you can omit the switch off and on.
Clip onto the emitter lead of one output resistor. switch on. Measure the voltage to the output. that gets you the Vre of one device.
Switch off. move the clip on probe to the next device. Repeat until you have all four Vre.
If you have a steady hand and want to accept the risk of blowing up the amplifier by shorting between Collector and Emitter, then you can omit the switch off and on.
Thanks AndrewT, Appreciate the help. Could you verify if the 0.01 5W resistors are the emitter resistors? Just want to confirm before testing with current.
Any other test points? Maybe directly on the transistors? You mention short CE, does that get me same voltage as I would get on the emitter resistor?
Noob questions, but want to be sure before trying. Also trying to read the schematic and learn this stuff. Thanks again.
Any other test points? Maybe directly on the transistors? You mention short CE, does that get me same voltage as I would get on the emitter resistor?
Noob questions, but want to be sure before trying. Also trying to read the schematic and learn this stuff. Thanks again.
Don't try to measure current.
Measure voltage drop and use that Vdrop to calculate current.
If you accidentally short the C to E with a slipped probe you will almost certainly destroy your amplifier.
R129, 130, 143 & 144 are the emitter resistors. They are marked as 0.1/5W, that means 0.1ohms and 5W power rating. Measuring 1mV for Vdrop means that 10mA of current is flowing. So you have a conversion: 10mA/mV
The resistors could be ±5% or ±10% so don't expect good accuracy. If you were building this yourself I would recommend you match emitter resistors to better than ±0.5% so that measurements later mean something useful.
Hint:
solder your emitter resistors in series with very long leads, so that your can probe/tap onto each lead during measurments that is about 5mm away from the body.
Pass a fixed current through the string of resistors.
Keep this fixed current accurately constant.
Measure the Vdrop of each resistor. Select out groups that have the same Vdrop ±0.25% (0.3mV difference in 120mV when 1.2A is passing, Pq = 0.144W, <3% of Pmax and they stay cool to cold).
The above method is so good at discriminating small differences in resistance that you can "measure" the resistance of the thick copper lead out of these resistors ! This will tell you if they are copper, or steel !!!!!
Measure voltage drop and use that Vdrop to calculate current.
If you accidentally short the C to E with a slipped probe you will almost certainly destroy your amplifier.
R129, 130, 143 & 144 are the emitter resistors. They are marked as 0.1/5W, that means 0.1ohms and 5W power rating. Measuring 1mV for Vdrop means that 10mA of current is flowing. So you have a conversion: 10mA/mV
The resistors could be ±5% or ±10% so don't expect good accuracy. If you were building this yourself I would recommend you match emitter resistors to better than ±0.5% so that measurements later mean something useful.
Hint:
solder your emitter resistors in series with very long leads, so that your can probe/tap onto each lead during measurments that is about 5mm away from the body.
Pass a fixed current through the string of resistors.
Keep this fixed current accurately constant.
Measure the Vdrop of each resistor. Select out groups that have the same Vdrop ±0.25% (0.3mV difference in 120mV when 1.2A is passing, Pq = 0.144W, <3% of Pmax and they stay cool to cold).
The above method is so good at discriminating small differences in resistance that you can "measure" the resistance of the thick copper lead out of these resistors ! This will tell you if they are copper, or steel !!!!!
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Thanks for the explanation.
I pulled the board and tested the emitter resistors. They all measured right at 0.001V, a couple would go back and forth 0.0001-0.002.
I also tested them all for resistance and all checked out at 0.01r. It seems to be within spec on my tests, but I don't have any specs to compare to from the manufacturer. I guess as long as the heat-sink is staying cool, it should be dissipating the heat enough?
I pulled the board and tested the emitter resistors. They all measured right at 0.001V, a couple would go back and forth 0.0001-0.002.
I also tested them all for resistance and all checked out at 0.01r. It seems to be within spec on my tests, but I don't have any specs to compare to from the manufacturer. I guess as long as the heat-sink is staying cool, it should be dissipating the heat enough?
measuring right down at the least significant digit (lsd) is not accurate with a DMM. Many are specified as ±(% of reading + 2 or 3 digits)
so a reading of 0.001Vdc means 0.001Vdc + 0.003 to 0.001 - 0.002, i.e. your voltage could be anywhere from +0.004Vdc to -0.002Vdc
You need a DMM that can read with a resolution about 10 times lower than your expected reading.
a 199.9Vdc and 199.9mVac reading DMM is a very useful tool for voltage readings of audio amplifiers. They are available cheaply typically <£10 <$15.
The 0.01ohms reading is extremely suspect.
What does your instrument read when you touch the probes together?
What does your instrument read when you touch the probes to the lead out on same side of the resistor?
so a reading of 0.001Vdc means 0.001Vdc + 0.003 to 0.001 - 0.002, i.e. your voltage could be anywhere from +0.004Vdc to -0.002Vdc
You need a DMM that can read with a resolution about 10 times lower than your expected reading.
a 199.9Vdc and 199.9mVac reading DMM is a very useful tool for voltage readings of audio amplifiers. They are available cheaply typically <£10 <$15.
The 0.01ohms reading is extremely suspect.
What does your instrument read when you touch the probes together?
What does your instrument read when you touch the probes to the lead out on same side of the resistor?
It reads 0.0 when I touch the leads together either on Ohms or AC/DC setting. It's a decent auto ranging DMM, but I honestly do t know the true rating for the accuracy or reading specifics.
Odd thing after I put the board back in, the left channel went out again. Messed with a few connectors and it came back on.
Put it on "auto-on" to let it sit and make sure that worked. When I clicked back on no left channel again.
Turned it off and turned off the auto-on setting. Came back for a brief time and then back off.
After checking voltages, noticed my 12Vdc was only showing 5Vdc. Traced it to a C1815 regulator on the power board. Changed it out and now I have 12Vdc back but still no left channel??
I checked all the transistors and they check good as do the resistors.
I don't hear both relays click on, think it's protection relay. Any way to test that or do I have to buy one and see if that was it?
Paul
Odd thing after I put the board back in, the left channel went out again. Messed with a few connectors and it came back on.
Put it on "auto-on" to let it sit and make sure that worked. When I clicked back on no left channel again.
Turned it off and turned off the auto-on setting. Came back for a brief time and then back off.
After checking voltages, noticed my 12Vdc was only showing 5Vdc. Traced it to a C1815 regulator on the power board. Changed it out and now I have 12Vdc back but still no left channel??
I checked all the transistors and they check good as do the resistors.
I don't hear both relays click on, think it's protection relay. Any way to test that or do I have to buy one and see if that was it?
Paul
A little more research and I think it is the relay. If I let it warm up a little playing only the right channel (5-10 mins) and then tap on the relay with a soft handled screwdriver, it will click on and the left channel plays. It will play as long as I don't turn it off, otherwise it's 50/50 if it the relay will turn on with power up. Almost like the contacts are getting stuck??? Not sure how a relay usually fails.
Edit - schematic says a JZ101 - 10A but nothing else. Any idea how to know what to order? I think its a SPST (only shows 1,2,3,4 contacts on schematic (1 & 2 being switched))
Edit - schematic says a JZ101 - 10A but nothing else. Any idea how to know what to order? I think its a SPST (only shows 1,2,3,4 contacts on schematic (1 & 2 being switched))
Able to read the side and get the part#. Any suggestions for a replacement? Should I replace both, so they are the same?
Goodsky RUDH-SH-112D (apparently a SPDT, 10A 12VDC) but can't find a replacement on digikey/mouser that matches size. 20.5Dx16.7Wx20.3H, with pins 12.2x12 according to the spec sheet I found for this relay on google.
Goodsky RUDH-SH-112D (apparently a SPDT, 10A 12VDC) but can't find a replacement on digikey/mouser that matches size. 20.5Dx16.7Wx20.3H, with pins 12.2x12 according to the spec sheet I found for this relay on google.
for an easy swap the relay pin out must be identical. that will take quite a bit of searching through datasheets to confirm it matches.
Unsoldering the relay from the multiple pins will not be easy !
If you want to use an off board relay, any relay with a good DC rating will do.
Check the coil voltage/resistance. Since the one you have is working, you can check this before it burns out.
Worth checking the voltage across the relay coil while it is powered on.
If the switching is faulty it may be only just closing on one contact, but holding the other partially open..
Unsoldering the relay from the multiple pins will not be easy !
If you want to use an off board relay, any relay with a good DC rating will do.
Check the coil voltage/resistance. Since the one you have is working, you can check this before it burns out.
Worth checking the voltage across the relay coil while it is powered on.
If the switching is faulty it may be only just closing on one contact, but holding the other partially open..
I found the exact same model relays, so ordered those to make it easy. Should be here. Ext week and I'll post how it goes.
Thanks for the help, suggestions and instruction it's much appreciated.
Paul
Thanks for the help, suggestions and instruction it's much appreciated.
Paul
Sorry for the delay, life gets in the way. Well it wasn't the relay and possibly not the 2SA1943 transistor (Q109) causing the issue(s). It seems it was the transistor (Q120) just to the left of the left channel relay. touched it with the DMM probe and the relay switched off, touched again and the relay clicked back on.
Took the board out and didn't see anything wrong and it measured good with the DMM. I went ahead and removed it (Q120), checked it again with the DMM, then cleaned the holes and re-installed, this time using a little extra pressure to get the legs seated and soldered good. Relays kicked on and worked.
Amp has been working fine ever since. I have tried to run it in all configurations to make sure no weak link was overlooked. So I've tried it stereo, bridged and using always-on and the auto sense (turning it off and on with a signal) and it seems to be working as it should with no more issues.
Thanks for the advice and assistance.
Took the board out and didn't see anything wrong and it measured good with the DMM. I went ahead and removed it (Q120), checked it again with the DMM, then cleaned the holes and re-installed, this time using a little extra pressure to get the legs seated and soldered good. Relays kicked on and worked.
Amp has been working fine ever since. I have tried to run it in all configurations to make sure no weak link was overlooked. So I've tried it stereo, bridged and using always-on and the auto sense (turning it off and on with a signal) and it seems to be working as it should with no more issues.
Thanks for the advice and assistance.
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