Flaxmill19
Active Member
Hi All,
Well, I just spent the entire weekend making changes to my 140 Power Amp, this was going to be the final tinker, refer previous post (http://www.audiokarma.org/forums/showthread.php?t=562617). The work carried out over the weekend was the following:
Replace the C701 1.0 µF films with Mundorf Supremes on each amp board
Replace the trim resistors with Bourns trimmers (2 on each amp board & 2 on each meter board)
Replace for transistors on the left amp board (H705, H706, H707 & H708). These had already been replaced on the right amp board and fixed a fault, just want to equal things up.
Replace meter velum paper
Replace shielded cable from RCA inputs to gain control, the from gain control to amp board (both channels). Silver coated copper wire shielded cable used.
Dexoit the gain controls
Replace the RCA input connections with gold plated connections.
Replaced the relay (after initial power up)
When I powered the amp up through a DBT the VU meters turned on, and both peak meters were on. I then checked the DC off set and this was -31 mV and -45 mV for the left & right channels respectively. Could not adjust the measurement by turning either R471.
I then checked the Bias and although close to the specification, I could adjust the reading on both R742.
I then noticed that the relay was not clicking on, I imputed 190mV @ 1kHz and noted that I had no output voltage from either channel. This makes sense if the relay is not turning on, I suppose! As I had a new relay I replaced it, and you guessed it, no change.
I have noticed that Relay Circuit (PN00) resistor RN09 (120 x 3W) becomes very hot after a short time. I am not leaving the power on for more than about 30 seconds and after this it’s quite hot to touch. It also smells (burning dirt, dust), suggesting that it doesn’t normally run that hot.
I have rechecked all the wiring to ensure that my replacement wiring is correct and the I have refitted my wiring changes from the previous changes correctly, as far as I can ascertain, I have done everything correctly!
My thoughts are something in the power supply not the amp or meter boards, as this seems to effect each channel the same, so you would think, it would be the power supply or relay circuit (PN00), I have checked the voltage at the power filter capacitors and its about 40VDC (that about right).
I have checked the voltage at JN06 & JN07 where they connect to PN00. This is with no input voltage, they both read about 6.2 VAC. I then disconnected the wire on JN07 and the voltage at the termination on the PN00 board was 4.5VAC and the voltage on the wire from the amp board was 6.2 VDC.
I think that I am just going to have to pull things down and isolate and test as I do so to try and find the fault.
I would be over the moon if an AK’er could provide me with some assistance.
Could it be anything I changed? Or something damaged during the work being carried out?
Any assistance would be greatly appreciated.
Tony
PS Attached a schematic for those interested, it poor quality, I will attach a better version later. I have attached a better quality Schematic in post #3.
Well, I just spent the entire weekend making changes to my 140 Power Amp, this was going to be the final tinker, refer previous post (http://www.audiokarma.org/forums/showthread.php?t=562617). The work carried out over the weekend was the following:
Replace the C701 1.0 µF films with Mundorf Supremes on each amp board
Replace the trim resistors with Bourns trimmers (2 on each amp board & 2 on each meter board)
Replace for transistors on the left amp board (H705, H706, H707 & H708). These had already been replaced on the right amp board and fixed a fault, just want to equal things up.
Replace meter velum paper
Replace shielded cable from RCA inputs to gain control, the from gain control to amp board (both channels). Silver coated copper wire shielded cable used.
Dexoit the gain controls
Replace the RCA input connections with gold plated connections.
Replaced the relay (after initial power up)
When I powered the amp up through a DBT the VU meters turned on, and both peak meters were on. I then checked the DC off set and this was -31 mV and -45 mV for the left & right channels respectively. Could not adjust the measurement by turning either R471.
I then checked the Bias and although close to the specification, I could adjust the reading on both R742.
I then noticed that the relay was not clicking on, I imputed 190mV @ 1kHz and noted that I had no output voltage from either channel. This makes sense if the relay is not turning on, I suppose! As I had a new relay I replaced it, and you guessed it, no change.
I have noticed that Relay Circuit (PN00) resistor RN09 (120 x 3W) becomes very hot after a short time. I am not leaving the power on for more than about 30 seconds and after this it’s quite hot to touch. It also smells (burning dirt, dust), suggesting that it doesn’t normally run that hot.
I have rechecked all the wiring to ensure that my replacement wiring is correct and the I have refitted my wiring changes from the previous changes correctly, as far as I can ascertain, I have done everything correctly!
My thoughts are something in the power supply not the amp or meter boards, as this seems to effect each channel the same, so you would think, it would be the power supply or relay circuit (PN00), I have checked the voltage at the power filter capacitors and its about 40VDC (that about right).
I have checked the voltage at JN06 & JN07 where they connect to PN00. This is with no input voltage, they both read about 6.2 VAC. I then disconnected the wire on JN07 and the voltage at the termination on the PN00 board was 4.5VAC and the voltage on the wire from the amp board was 6.2 VDC.
I think that I am just going to have to pull things down and isolate and test as I do so to try and find the fault.
I would be over the moon if an AK’er could provide me with some assistance.
Could it be anything I changed? Or something damaged during the work being carried out?
Any assistance would be greatly appreciated.
Tony
PS Attached a schematic for those interested, it poor quality, I will attach a better version later. I have attached a better quality Schematic in post #3.
Attachments
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