Another Kenwood KR-9600 Power Supply / Protection Mode Repair
- Thread starter bhuskins
- Start date
The C2240BL's are very consistent in gain...the C1845's will be all over the map. The discontinued higher gain C1845's were pretty good as far as consistency, but we're down to the mfgr. dregs as these parts are phased out.
The actual gain you see will depend on the meter. Qe1 and Qe2 should be matched within 5%, and Qe4 and Qe5 as well (if possible). Hfe in the later stages is not so critical.
The actual gain you see will depend on the meter. Qe1 and Qe2 should be matched within 5%, and Qe4 and Qe5 as well (if possible). Hfe in the later stages is not so critical.
bhuskins
Super Member
Final question before installing the amp module...
With the amp board recapped and all new transistors and diodes, without the module installed if powered on should pins 1~10 read:
Pin 1:67v
Pin 3:1v
Pin 5:0v
Pin 6:0v
Pin 7:-.05v
Pin 8:-1.2v
Pin 10:-67v
I'd assume no and that pins 3 and 8 won't read correctly without the module installed but I wanted to check for sure and to see if you know what I should expect.
Normally, I wouldn't be so concerned but obviously with such an expensive and hard to find module I don't want to screw it up.
And yes I'll still be bringing it up with a variac once it's all back together.
With the amp board recapped and all new transistors and diodes, without the module installed if powered on should pins 1~10 read:
Pin 1:67v
Pin 3:1v
Pin 5:0v
Pin 6:0v
Pin 7:-.05v
Pin 8:-1.2v
Pin 10:-67v
I'd assume no and that pins 3 and 8 won't read correctly without the module installed but I wanted to check for sure and to see if you know what I should expect.
Normally, I wouldn't be so concerned but obviously with such an expensive and hard to find module I don't want to screw it up.
And yes I'll still be bringing it up with a variac once it's all back together.
Probably, but there's not a lot of point in powering up without the module in place. And I don't recommend a variac, as they are not current-limited.
bhuskins
Super Member
Yes correct...I actually meant to say DBT...as long as the amp board is sound I should be ok...really the only pins relevant are the wire wrapped pins I suppose. Both boards read the same before dissasembly (but after the one module was removed.)
Good channel (bad channel with module removed)
Pin 1:-.8mV (-.1mV)
Pin 2: Ground (same)
Pin 3: 71v (72.7v)
Pin 4: Ground (same)
Pin 5: -71.5v (-72.9v)
Pin 6: 133mV (31mV)
Pin 7: 71v (72.5v)
So it looks to be all good in prep for the rebuilt boards
Good channel (bad channel with module removed)
Pin 1:-.8mV (-.1mV)
Pin 2: Ground (same)
Pin 3: 71v (72.7v)
Pin 4: Ground (same)
Pin 5: -71.5v (-72.9v)
Pin 6: 133mV (31mV)
Pin 7: 71v (72.5v)
So it looks to be all good in prep for the rebuilt boards
bhuskins
Super Member
Some time has transpired and Glenn has been helping me with the 9600. Both amp boards have been rebuilt and reinstalled and we are in the process of getting it back up and running. Currently the unit passes a DBT but the voltages are wrong.
Glenn had asked me to post some readings here and we'll be continuing the discussion here.
With a 200w dbt in place
The "bad" channel reads the offset at:
pin 5 of the amp module >>> 32.2v
wirewrap pin 6 >>> 32.2v
the "good" channel reads the offset at:
pin 5 of the amp module >>> 6.5mV
wirewrap pin 6 >>> -2.6mV
The relay does not engage...
Glenn had asked me to post some readings here and we'll be continuing the discussion here.
With a 200w dbt in place
The "bad" channel reads the offset at:
pin 5 of the amp module >>> 32.2v
wirewrap pin 6 >>> 32.2v
the "good" channel reads the offset at:
pin 5 of the amp module >>> 6.5mV
wirewrap pin 6 >>> -2.6mV
The relay does not engage...
ecluser
Super Member
There was a way to test the amp board without the power module. With the module removed you can install a 1k resistor between pins 3 and 5 (of the power module), and another 1k resistor between pins 8 and 5 (of the power module). With 1k resistors the voltages at pins 3 and 8 should be +7V and -7V respectively. Sorry to be a little late on that suggestion. That said, I don't think that the power module is bad. I also think that this high offset voltage will not destroy the power module if there is no load. It is thus safe to keep the power module installed.
Did you compare the voltage at the zener De3, between L and R channel?
With this high offset voltage, Ce3 is probably bad now. I would replace Ce3 and it is a good practice to shunt the feedback capacitor with diodes, one diode in each direction. That prevents failure of the capacitor in situations where there is a large DC voltage at the output.
Can you measure the DC voltage at the collectors of Qe1, Qe2, Qe4 and Qe5?
Actually Qe7 is driven too hard. That pull the power module toward the positive supply rail.
Did you compare the voltage at the zener De3, between L and R channel?
With this high offset voltage, Ce3 is probably bad now. I would replace Ce3 and it is a good practice to shunt the feedback capacitor with diodes, one diode in each direction. That prevents failure of the capacitor in situations where there is a large DC voltage at the output.
Can you measure the DC voltage at the collectors of Qe1, Qe2, Qe4 and Qe5?
Actually Qe7 is driven too hard. That pull the power module toward the positive supply rail.
ecluser
Super Member
With +32V at the output I estimate (unless Ce3 is shorted) that the base voltage of Qe2 is of the order of +26V, the common emitters of Qe1 and Qe2 are at +25V, the base of Qe1 is at +19V, and the current in Re3 is in the opposite direction as it should be. In other words, this is not an "offset voltage" in the proper sense of the word, because the input stage doesn't work at all. We need more voltage measurements, in each stage, to have a better comprehension of the actual situation.
bhuskins
Super Member
So being that Glenn completely rebuilt both amp boards and as a troubleshooting step along the way Glenn had me swap the amp modules between the 2 boards after the rebuild, I'm sure we would prefer to avoid removing the modules again to help protect the pads unless absolutely necessary. I'm just looking to follow Glenn's lead here since he has some meat in the game. So, what's the next step Glenn? I'm happy to pull the module and install a dummy load, etc but didn't want to proceed without your blessing so to speak.
bhuskins
Super Member
This is where I was a bit confused on the request...so I should leave the module in place and also install 1k resistors as specified?
And, then once they are in place on the bad channel only, take the voltage readings below?
And should I go ahead and replace ce3 1st?
I just want to make sure i follow the instructions correctly.
bhuskins
Super Member
Sorry for the delay...here's what the "bad" channel reads with a 200w DBT in place that goes dim right after power up. Readings were taken about 10 minutes after turn on with the ground at the main chassis ground connection near the main caps. Also, the relay does not engage after power up.
Cathode of De3 23.59v
Collector of Qe1 23.59v
Collector of Qe2 22.8v
Collector of Qe4 50.2v
Collector of Qe5 52.8v
Cathode of De3 23.59v
Collector of Qe1 23.59v
Collector of Qe2 22.8v
Collector of Qe4 50.2v
Collector of Qe5 52.8v
