Here are more readings RE: the image you sent......
R3/TR1/TR2 = 0.036V
R4 = -43V
R5= -43V
R10= -43V
D1= +43V
R12/TR5 = 0.093V
C6/TR4/RV1 = 0.094V
MM
R3/TR1/TR2 = 0.036V
R4 = -43V
R5= -43V
R10= -43V
D1= +43V
R12/TR5 = 0.093V
C6/TR4/RV1 = 0.094V
MM
Your voltage readings don't quite add up!
Please confirm:
Voltage across R10 = 1.5V?
Voltage across R11=?
Voltage between junction of TR3/R9 and 0V (0V=meter -ve)
Voltage between junction of TR4/RV1 and 0V (0V=meter -ve)
Voltage between junction of TR5/R12 and 0V (0V=meter -ve)
Its strange both exhibit identical symptoms.
The fact the output is at essentially zero volts suggests its basically OK. You need to confirm the preset really is 1k and 100 ohm. If that is OK then you need to check that the voltage across the preset rises as you turn it. Typically you would need around 1.1 to 1.5 volts give or take in order to bias the FET's on and draw the required current. As currentflow says, the voltage across R11 is worth checking. You should see around 0.5 volts corresponding to around 5ma flowing. That 5ma flows through the preset and enables the volt drop to bias on the FET's to be developed. So around 200 ohm on the pot would be in the ballpark... you mention around a quarter turn.
Check the value of the presets.
The fact the output is at essentially zero volts suggests its basically OK. You need to confirm the preset really is 1k and 100 ohm. If that is OK then you need to check that the voltage across the preset rises as you turn it. Typically you would need around 1.1 to 1.5 volts give or take in order to bias the FET's on and draw the required current. As currentflow says, the voltage across R11 is worth checking. You should see around 0.5 volts corresponding to around 5ma flowing. That 5ma flows through the preset and enables the volt drop to bias on the FET's to be developed. So around 200 ohm on the pot would be in the ballpark... you mention around a quarter turn.
Check the value of the presets.
Hi,
The readings I posted were WRT gnd and not 'across' any component.
Here are the readings you asked for.....
Voltage across R10 = 1.11V
Voltage across R11= 0.592V
Voltage between junction of TR3/R9 and 0V = -43V
Voltage between junction of TR4/RV1 and 0V =0.092V
Voltage between junction of TR5/R12 and 0V =0.373V
I hope this helps as I am at a loss on this one! 😉
MM
The readings I posted were WRT gnd and not 'across' any component.
Here are the readings you asked for.....
Voltage across R10 = 1.11V
Voltage across R11= 0.592V
Voltage between junction of TR3/R9 and 0V = -43V
Voltage between junction of TR4/RV1 and 0V =0.092V
Voltage between junction of TR5/R12 and 0V =0.373V
I hope this helps as I am at a loss on this one! 😉
MM
The voltages measured at the collectors of TR5 and TR4 should indicate what is flowing through RV1+R12 (for a measured RV1). Either RV1 is too low in value, or there isn't enough current out of TR5 collector to develop sufficient voltage drop across RV1 to bias TR6/7 into conduction.
The middle one seems suspect TR3/R9 and 0V = -43V I would have expected around -15 to -18 volts on the collector of TR3
The others are fine... check that value of preset 🙂 You haven't enough voltage developed across it to turn the FET's on and yet you have around 0.6 volts across R11. That equates to 6ma which should drop 6 volts across a 1k preset.
The others are fine... check that value of preset 🙂 You haven't enough voltage developed across it to turn the FET's on and yet you have around 0.6 volts across R11. That equates to 6ma which should drop 6 volts across a 1k preset.
The amp would actually still work under those conditions but the current in the output (and preset) would be higher.
At the moment my money is on the preset 😉
RV1 is still fully clockwise during the above tests (as I have not yet got to the setting the current stage as there is no current when turning RV1).
Setting RV1 by eye (about 206R if I remember in the last test) gives about 1.11V drop across it. It *is* a 1K preset. Says so on the case and measures it too.
TR3 measured in circuit is not shorted.
Thanks for your time, especially at this time of year! 🙂
MM
Setting RV1 by eye (about 206R if I remember in the last test) gives about 1.11V drop across it. It *is* a 1K preset. Says so on the case and measures it too.
TR3 measured in circuit is not shorted.
Thanks for your time, especially at this time of year! 🙂
MM
Voltage across RV1 does increase as the pot is turned, at half turn it was at just over 2V. - Remember that these are NEW presets, just installed.
MM
MM
The voltage was measured across the pot from the junction with R12 to the other side of the pot.
I found the original set up instructions and measuring output current isn't in it, so I have not tried that.
What I *am* measuring is the positive rail input current (DMM set to 300mA in series with the +44V input, red to PSU and black to amp input). That's how they say to do it (not wishing to sound rude) 😉
Hope this helps (me) ! 🙂
MM
I found the original set up instructions and measuring output current isn't in it, so I have not tried that.
What I *am* measuring is the positive rail input current (DMM set to 300mA in series with the +44V input, red to PSU and black to amp input). That's how they say to do it (not wishing to sound rude) 😉
Hope this helps (me) ! 🙂
MM
srh,
BANG On The MONEY!!!!!
I removed the cover and the fuse in the fluke looked just fine, but I tested it anyway and what do ya know???
OK so now another question....... What current should I set? - The original instructions say 50mA, yet I see others that say 100mA..... What do you guys think?
Thanks a ton! 🙂 🙂 🙂
MM
BANG On The MONEY!!!!!
I removed the cover and the fuse in the fluke looked just fine, but I tested it anyway and what do ya know???
OK so now another question....... What current should I set? - The original instructions say 50mA, yet I see others that say 100mA..... What do you guys think?
Thanks a ton! 🙂 🙂 🙂
MM
Lol 🙂 We've all been caught with things like that.
100 ma is perfect the lateral FET's, 50 is a bit low.
Because the design is heavily dependent on supply voltage for final adjustment make sure you are on full mains... no bulb tester.
100 ma is perfect the lateral FET's, 50 is a bit low.
Because the design is heavily dependent on supply voltage for final adjustment make sure you are on full mains... no bulb tester.
The voltage measurement across RV1 showing just over 2V max is looking good. From the notes I have discovered online, you are right in that the idle current is measured in the positive rail. This should be set at 100mA. If your meter is not registering any current, check its internal fuse is intact or, if you have a spare 10 ohm 0.25 watt resistor, place this in series with the positive rail and measure the DC voltage across it. Adjust RV1 to read 1V.
Edit: I shouldn't get so distracted during edits, too much happens in the meantime 🙂
Edit: I shouldn't get so distracted during edits, too much happens in the meantime 🙂
It might not be over yet !!! 😉
But this one module will sit with full mains for half an hour and hopefully will be OK. Mosfets at about 30C and I must buy some more fuses for the meter - LOL! 🙂
Will test the other module tomorrow now I expect - But THANK YOU ALL for all the support and help, it *really* makes a difference at a time like this!
MM
But this one module will sit with full mains for half an hour and hopefully will be OK. Mosfets at about 30C and I must buy some more fuses for the meter - LOL! 🙂
Will test the other module tomorrow now I expect - But THANK YOU ALL for all the support and help, it *really* makes a difference at a time like this!
MM
I'm sure it will be fine. Just remember to follow the same procedure (preset on minimum resistance to start) and I always advise a bulb tester... simple mistakes happen and using one could easily save a pair of expensive FET's.
After 10 minutes the mosfets (and the TR5 area) were above 45C and so I turned it off at that point. Current was still 100mA (give or take 2%) so I guess that this module is OK......Now on to the next! 🙂
MM
MM
The method I use to measure Iq is to insert a low value resistor in the supply rail and measure the voltage drop across it. If there is a fault the resistor smokes and the fuse in your multimeter survives!! Note that this method is for output stages that are followers.
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