I am working on a pair on L08m Kenwood Mono blocks- one works fine, the other has a NFB (RL1) relay that keeps clicking. The rate of clicking is associated with the offset adjustment.
The problem is I do not have 24v on the coil, and when I trace this back it comes from one side of R112 in the attached diagram. The other side or R112 is attached to the Collector of Q47, which in the bad amp is 0v, whereas it is 64v on the good amp. So I surmise it is not being turned on. Q46 and Q47 drive this relay.
As I trace this back-Q39 on the good amp has 8v on the collector, where as the bad amp has about 3v (fluctuating).
I have repalced all the caps, tested out of circuit all the transistors and tested in circuit all the diodes-and replaced a couple-all the resistors have been tested in or out of circuit depending on their measurement, again all test good.
I have checked (and checked again) all cap values and polarities, but I am at a loss to understand why the circuit is misbehaving. The voltage at the junction of C29 and D33 is 12v on both good and bad, and the B+ measures at 65v at the emitter of Q46 and Q45, and both there bases are at 64v (or so).
On the good one the collector of Q46 is 65v (as is the emitter of Q47), where as it is 55v on the bad one.
So I think something is not being turned on
I have attached the overall circuit, page on the relay operation and circuit oif that section with voltages. The additional complication is Q40 and Q41 which are not shown on the circuit and are mounted on the PCB and listed in the parts list.
I will try and trace out where they connect. Q40 shares a common collector with Q39, other than that their voltages are the same on the good and bad units
any thoughts as to where I should be looking?
The problem is I do not have 24v on the coil, and when I trace this back it comes from one side of R112 in the attached diagram. The other side or R112 is attached to the Collector of Q47, which in the bad amp is 0v, whereas it is 64v on the good amp. So I surmise it is not being turned on. Q46 and Q47 drive this relay.
As I trace this back-Q39 on the good amp has 8v on the collector, where as the bad amp has about 3v (fluctuating).
I have repalced all the caps, tested out of circuit all the transistors and tested in circuit all the diodes-and replaced a couple-all the resistors have been tested in or out of circuit depending on their measurement, again all test good.
I have checked (and checked again) all cap values and polarities, but I am at a loss to understand why the circuit is misbehaving. The voltage at the junction of C29 and D33 is 12v on both good and bad, and the B+ measures at 65v at the emitter of Q46 and Q45, and both there bases are at 64v (or so).
On the good one the collector of Q46 is 65v (as is the emitter of Q47), where as it is 55v on the bad one.
So I think something is not being turned on
I have attached the overall circuit, page on the relay operation and circuit oif that section with voltages. The additional complication is Q40 and Q41 which are not shown on the circuit and are mounted on the PCB and listed in the parts list.
I will try and trace out where they connect. Q40 shares a common collector with Q39, other than that their voltages are the same on the good and bad units
any thoughts as to where I should be looking?
Q39base is expected to be 0Vdc (or a few mV) however it's probably more (turned on)
dragging down the 8V. Check DC offset for problematic channel/unit, measure Vdc
at emitter resistors to GND.
dragging down the 8V. Check DC offset for problematic channel/unit, measure Vdc
at emitter resistors to GND.
I have been testing with the drivers and outputs disconnected. Prior to that I had measured Q39base and got 0v
@mbz- yes you are right, there is between 50mv and 100mv floating on the base of Q39. I will investigate the potential causes (Q25/Q26/Q27/Q28 and associated circuitry) and report back
thank you
Peter
thank you
Peter
Thinking out loud, voltage on Q42e is low due to higher than normal current
through R102. Where is that current going? Q39? though would have wanted to
see more than 100mV at Q39b. Q42? C30? R103,104(unlikely) Q43,Q44?
What is the voltage on Q43b?
through R102. Where is that current going? Q39? though would have wanted to
see more than 100mV at Q39b. Q42? C30? R103,104(unlikely) Q43,Q44?
What is the voltage on Q43b?
Thanks- the voltage on the base of Q43 is 0.3v, and fluctuates.
I measured Q25..Q28- all of them are measuring wrong!
I am beginning to suspect that there may be an earth that is not connected- so will check the continuity of all the cables
Peter
I measured Q25..Q28- all of them are measuring wrong!
I am beginning to suspect that there may be an earth that is not connected- so will check the continuity of all the cables
Peter
so I have checked all the cables and earths and all seems good.
There is 0.3v (fluctuates) on the output, which is going to the base of Q39.
Q31..Q38 are not connected (ie. drivers and outputs)
Q29 and Q30 have base voltages at +/11.8v as per circuit.
Q25 should have emitter voltage of 1.8v, however it is 6.9v, yet D11 anode is 0v, and worse collector of Q25 is 66v! It is a 2SC1279s- and I am looking at replacements, though I am unsure how 66v gets to the collector.
I am working on @mbz theory that the 0.3v is switching on Q39.
any help appreciated
Peter
There is 0.3v (fluctuates) on the output, which is going to the base of Q39.
Q31..Q38 are not connected (ie. drivers and outputs)
Q29 and Q30 have base voltages at +/11.8v as per circuit.
Q25 should have emitter voltage of 1.8v, however it is 6.9v, yet D11 anode is 0v, and worse collector of Q25 is 66v! It is a 2SC1279s- and I am looking at replacements, though I am unsure how 66v gets to the collector.
I am working on @mbz theory that the 0.3v is switching on Q39.
any help appreciated
Peter
further voltages:
Q25 e 6.6v/b1.8/c66v note b jumps to 2.1v on relay click
circuit states Q25 e 1.v/b1.3v
Q26 e-1.7v/b-2.7/c 0.3v- note b jumps to 13v on relay click
circuit states Q26 e -1.8v/b-1.3v
Q27 e 0.3v/0,3v/c6.6v
circuit state Q27 b 0v
Q28 e 0.3v/b 0.3v/c-2.7
circuit states Q28 b 0v
so I am perplexed how the rail voltage is getting to Q25 collector
Q25 e 6.6v/b1.8/c66v note b jumps to 2.1v on relay click
circuit states Q25 e 1.v/b1.3v
Q26 e-1.7v/b-2.7/c 0.3v- note b jumps to 13v on relay click
circuit states Q26 e -1.8v/b-1.3v
Q27 e 0.3v/0,3v/c6.6v
circuit state Q27 b 0v
Q28 e 0.3v/b 0.3v/c-2.7
circuit states Q28 b 0v
so I am perplexed how the rail voltage is getting to Q25 collector
The amp looks like it's in protect mode.Q25c(66V) is on the spkr line. Q25e should be
"3xVbe" (Q29, Q31, Q35//5//7) ie, about 1.8V. Maybe 2 problems, Q25c(66V) caused by
shorted/open driver/output transistor, Q25e(6.9V) might be due to 66V "feed back".
D11 cathode should be 0V.
Need to audit driver/output transistors, ie, dc voltages to GND for Q29b/c/e,,,Q38b/c/e.
"3xVbe" (Q29, Q31, Q35//5//7) ie, about 1.8V. Maybe 2 problems, Q25c(66V) caused by
shorted/open driver/output transistor, Q25e(6.9V) might be due to 66V "feed back".
D11 cathode should be 0V.
Need to audit driver/output transistors, ie, dc voltages to GND for Q29b/c/e,,,Q38b/c/e.
thanks @mbz- all the drivers and outputs are disconnect- they are on cables- I will check for shorts on the cables themselves
Q29/Q30 seem OK- base is +ve and -ve 1.8 as they should be
Q29/Q30 seem OK- base is +ve and -ve 1.8 as they should be
Schematic shows Q25c(66V), Q26c(0.3V), Q27e(0.3V), Q28e(0.3V) are
all connected and should be at the same voltage. Possibly a burnt
track in the area of Q25c?
all connected and should be at the same voltage. Possibly a burnt
track in the area of Q25c?
I gotta be looking at the wrong schematic, Q25e(6.6V) is connected to Q29b(1.8V)
should be same voltage.
should be same voltage.
OK, Q25e,c voltages is a red herring, Q29,30 base voltages at +/-1.8Vdc is good. Fact that
spkr relay clicks indicates no excessive Vdc, issue remains no click on NFB relay
spkr relay clicks indicates no excessive Vdc, issue remains no click on NFB relay
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Looks like D29,,32 are for -ve dc offset and Q39 for +ve offset.
300mV at Q39b is marginal for protection, does LED D39 turn on?
Expect not since spkr relay does kick in. I need to go over Q46,7
voltages
300mV at Q39b is marginal for protection, does LED D39 turn on?
Expect not since spkr relay does kick in. I need to go over Q46,7
voltages
Q46 base is 66v (rail voltage)
C32 replaced - all caps have been replaced
Q46 tested out of circuit as OK, Q 47 also tested good but replaced (KSA992)
C32 replaced - all caps have been replaced
Q46 tested out of circuit as OK, Q 47 also tested good but replaced (KSA992)
D39 does turn on
and the NFB relay keeps clicking- there is no 25v to the coil- (from R112- which in turn gets voltage from the collector of Q47- the Q46 and Q47 Voltages are:
Q46 e 67v b 66v c 56v-Note Q46c jumps from 56v to 62v each click of relay
Q47 e 56v b 66v c 0v -Note Q47e jumps from 56v to 62v on each relay click
Q47c (0v) should be 66v and then R112 drops this to 25v to drive relay
I do not understand why Q47c is not being turned on?
and the NFB relay keeps clicking- there is no 25v to the coil- (from R112- which in turn gets voltage from the collector of Q47- the Q46 and Q47 Voltages are:
Q46 e 67v b 66v c 56v-Note Q46c jumps from 56v to 62v each click of relay
Q47 e 56v b 66v c 0v -Note Q47e jumps from 56v to 62v on each relay click
Q47c (0v) should be 66v and then R112 drops this to 25v to drive relay
I do not understand why Q47c is not being turned on?