Had just buttoned up the amp after the latest repairs. Switched on power and there was a snappy spark sound near to the power switch, the amp didn’t start working and mains power was immediately switched off at the wall plug. No magic smoke occurred.
Looking inside I can see that the blue lead connected to the power switch has perished/disconnected from the switch. It was just resting on the pcb below.
Have now reconnected it. Powered on again at the wall mains plug with the C4's power switch in the 'On' position but again no response.
Fuses fine. No visibly damaged components.
How to proceed and what to check or replace?
How does one go about testing a reed relay? There's a RL 6442 (RY301) which I'd like to test but don't know how to.
Looking inside I can see that the blue lead connected to the power switch has perished/disconnected from the switch. It was just resting on the pcb below.
Have now reconnected it. Powered on again at the wall mains plug with the C4's power switch in the 'On' position but again no response.
Fuses fine. No visibly damaged components.
How to proceed and what to check or replace?
How does one go about testing a reed relay? There's a RL 6442 (RY301) which I'd like to test but don't know how to.
Carefully check for mains AC voltaged at the switched outlets at the rear, these are fed after the power switch so no/low volts would point to a faulty power switch. Warning, this is mains AC voltage.
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Thanks MBZ. Hope things are well with you.
I’m a bit anxious about working on the amp while it’s in this state.
I’m thinking, correct me if I’m wrong, but following the blue lead’s disconnection (it was probably disconnected at the time I switched on the mains wall socket while the C4 power switch was in the ‘on’ position) a possible component failure would be the reed relay on the flat amp board?
I have an identical working ‘spare’ that I can pull from my A1 amp. Thinking of swapping it in to the C4 and seeing how this goes.
Sound like a reasonable plan?
If so, are there any other likely components to check or replace, or would the reed relay have taken the hit and protected the rest?
Also, I can access the power switch, could I test it with a DMM to see if it’s working correctly. It’s action feels the same as it previously did and no visible scorch marks on it.
I’m a bit anxious about working on the amp while it’s in this state.
I’m thinking, correct me if I’m wrong, but following the blue lead’s disconnection (it was probably disconnected at the time I switched on the mains wall socket while the C4 power switch was in the ‘on’ position) a possible component failure would be the reed relay on the flat amp board?
I have an identical working ‘spare’ that I can pull from my A1 amp. Thinking of swapping it in to the C4 and seeing how this goes.
Sound like a reasonable plan?
If so, are there any other likely components to check or replace, or would the reed relay have taken the hit and protected the rest?
Also, I can access the power switch, could I test it with a DMM to see if it’s working correctly. It’s action feels the same as it previously did and no visible scorch marks on it.
Hard for me to see the connection between the blue wire and the relay mentioned.
The blue wire (AC active?) connects to the units power switch, from there it connects to the
transformer primary, the flow is then normal after this, ie, transformer secondary, rectification,
main filter caps then voltage regulation. So quite a lot of electronics before reaching the relay.
The spark was caused by the blue wire touching the amps chassis/GND, would have expected this to
trip the house fuse (since it's before the amps fuse).
Suggest do a health check of the power supply, check for mains ac at the switched outlets then check
the +/-30V and +/-45V regulated supply, the relays are powered by the -12Vac, possibly there is damage to
the relay control circuit TR621,2,3,4. Check Vdc at D305 anode, expect 12Vdc (-11.1 in sm)
The blue wire (AC active?) connects to the units power switch, from there it connects to the
transformer primary, the flow is then normal after this, ie, transformer secondary, rectification,
main filter caps then voltage regulation. So quite a lot of electronics before reaching the relay.
The spark was caused by the blue wire touching the amps chassis/GND, would have expected this to
trip the house fuse (since it's before the amps fuse).
Suggest do a health check of the power supply, check for mains ac at the switched outlets then check
the +/-30V and +/-45V regulated supply, the relays are powered by the -12Vac, possibly there is damage to
the relay control circuit TR621,2,3,4. Check Vdc at D305 anode, expect 12Vdc (-11.1 in sm)
Thanks for your help MBZ.
Can’t be sure what the blue lead touched when power went on.
Didn’t see a spark, but heard something like one..
(I’m quite apprehensive about applying power to this unit and taking measurements while it’s in this state. )
So, please could you tell me exactly where to place red and black lead of DMM on which RCA jack. What setting to have the DMM (AC or DC, voltage grouping etc)
I’ll set up the DMM and connect leads with the wall switch off, but the amp power switch on... and then switch on the mains wall switch and see what reading comes up.
Can then repeat on other locations on the amp.
Sound like a plan in this situation?
Thanks again.
Can’t be sure what the blue lead touched when power went on.
Didn’t see a spark, but heard something like one..
(I’m quite apprehensive about applying power to this unit and taking measurements while it’s in this state. )
So, please could you tell me exactly where to place red and black lead of DMM on which RCA jack. What setting to have the DMM (AC or DC, voltage grouping etc)
I’ll set up the DMM and connect leads with the wall switch off, but the amp power switch on... and then switch on the mains wall switch and see what reading comes up.
Can then repeat on other locations on the amp.
Sound like a plan in this situation?
Thanks again.
"would have expected this to
trip the house fuse (since it's before the amps fuse)."
Excellent MBZ!
I'd checked and then checked again every fuse in the amp, and all very good.
In the UK we have adapter plugs to convert a two pin to three pin mains socket.
Only now did I remember to check it.
Yes, a one amp fuse. Yes, it's blown.
Never blew before with this amp, the disconnected blue wire to the power switch had triggered it, at least I hope that that's the cause.
So, have replaced the adapter fuse with another 1 amp fuse and am reassembling the boards and chassis screws. Will report back when I power up.
Apologies for this 'oversight' and thanks for that sentence.
trip the house fuse (since it's before the amps fuse)."
Excellent MBZ!
I'd checked and then checked again every fuse in the amp, and all very good.
In the UK we have adapter plugs to convert a two pin to three pin mains socket.
Only now did I remember to check it.
Yes, a one amp fuse. Yes, it's blown.
Never blew before with this amp, the disconnected blue wire to the power switch had triggered it, at least I hope that that's the cause.
So, have replaced the adapter fuse with another 1 amp fuse and am reassembling the boards and chassis screws. Will report back when I power up.
Apologies for this 'oversight' and thanks for that sentence.
Hum present for AUX, TUNER rules out phono, so don't get distracted by it. 50Hz mains hum or 120Hz rectified which is more of a buzz. Do the Tone bypass and MODE (REV/STEREO/MONO) switches have any affect? Hum also present through headphones (separate amp)
Used 'signal Generator' app on iPhone and the hum is closest to 120Hz, but not a buzz, a smooth tone.
Tone bypass and MODE (REV/STEREO/MONO) switches have no effect or crackle but seem to affect sound correctly.
Yes, hum is also present through headphones (separate amp.)
Tone bypass and MODE (REV/STEREO/MONO) switches have no effect or crackle but seem to affect sound correctly.
Yes, hum is also present through headphones (separate amp.)
Cartridge Load...
At all settings PHONO is clear as a bell although with underlying hum (these switches were dismantled and cleaned) BUT at '100' setting the sound from the turntable goes super muffled almost distorted. All solder joins are fresh and look good.
Could there be a faulty component nearby? If so, which one(s) to test?
Phono cartridge is a MM.
At all settings PHONO is clear as a bell although with underlying hum (these switches were dismantled and cleaned) BUT at '100' setting the sound from the turntable goes super muffled almost distorted. All solder joins are fresh and look good.
Could there be a faulty component nearby? If so, which one(s) to test?
Phono cartridge is a MM.
With turntable connected and the ground from turntable to amp disconnected there is a clear buzzy hum which disappears, after some scratchy noises as the connection is made. Should point out that the ‘ground hum’ noise is a proper ‘buzz’ as you described. Very different to the amp’s own hum. If the turntable provides a 120Hz hum it might suggest that the amp’s hum is actually a 50Hz?
Also, the turntable hum and audio bleed through doesn’t occur between PHONO and AUX/TUNER when a record is playing.
Also, the turntable hum and audio bleed through doesn’t occur between PHONO and AUX/TUNER when a record is playing.
Rectified 100/120Hz hum would point to either a tired power supply or failing
part normally connected to (unregulated) power rails.
Power supply issue could be things like tired/leaky main caps or failure in
the regulated power supply. Power rails issues could be a tired diode or transistor
however this is less likely since problem is in both channels, suggest work through
(health check) power supply first.
An oscilloscope would be handy... assuming you don't have one then you could try
with a multimeter, the idea is to measure the AC ripple on the DC supply and then
decide if this is ok/consistent or not. Results will depend on how good your MM is,
best to use a cheap one rather than a true RMS type.
Measure AC voltage at the following test points on power supply board, +/-45, +/-30, -12
with black meter probe connected to chassis. If you get 0mV then test with black probe with
red probe connected to chassis.
The above is a long shot, preferred method is with an oscilloscope.
part normally connected to (unregulated) power rails.
Power supply issue could be things like tired/leaky main caps or failure in
the regulated power supply. Power rails issues could be a tired diode or transistor
however this is less likely since problem is in both channels, suggest work through
(health check) power supply first.
An oscilloscope would be handy... assuming you don't have one then you could try
with a multimeter, the idea is to measure the AC ripple on the DC supply and then
decide if this is ok/consistent or not. Results will depend on how good your MM is,
best to use a cheap one rather than a true RMS type.
Measure AC voltage at the following test points on power supply board, +/-45, +/-30, -12
with black meter probe connected to chassis. If you get 0mV then test with black probe with
red probe connected to chassis.
The above is a long shot, preferred method is with an oscilloscope.
Attachments
Hi MBZ.
Attached on this screenshot are the readings from my DMM, a Tenma 72-7925.
Different readings occurred dependent upon which AC setting was selected so I’ve provided both sets.
Please let me know what you think.
On the Neg 12 connection I tried the 'continuity/diode test” and there is perfect continuity, is that correct?
Also noticed that the amp’s power lead has a burn mark on it which has been taped over. I need to replace the power lead in any event but could a compromised power lead be a cause of this hum?
Attached on this screenshot are the readings from my DMM, a Tenma 72-7925.
Different readings occurred dependent upon which AC setting was selected so I’ve provided both sets.
Please let me know what you think.
On the Neg 12 connection I tried the 'continuity/diode test” and there is perfect continuity, is that correct?
Also noticed that the amp’s power lead has a burn mark on it which has been taped over. I need to replace the power lead in any event but could a compromised power lead be a cause of this hum?
The MM method described is very week to say the least, the next step is trying to
interpret the results. My take is that the +/-45 unregulated supply looks ok with
some symmetry in results depending on probe orientation. The minus 12 is also
unregulated, and results in same ballpark as +/-45 so looks ok.
You have listed "POS 30" twice, the second entry looks suspect since magnitudes are
in same ballpark as unregulated, suggest redo the measurement to confirm. Also need
to know if the second entry is for + or - 30.
Measure DC voltage at +/-30 pins. Consider replacing caps C315,6,7,8, C321,3,4 if
they are still original.
interpret the results. My take is that the +/-45 unregulated supply looks ok with
some symmetry in results depending on probe orientation. The minus 12 is also
unregulated, and results in same ballpark as +/-45 so looks ok.
You have listed "POS 30" twice, the second entry looks suspect since magnitudes are
in same ballpark as unregulated, suggest redo the measurement to confirm. Also need
to know if the second entry is for + or - 30.
Measure DC voltage at +/-30 pins. Consider replacing caps C315,6,7,8, C321,3,4 if
they are still original.
The -30 supply is off spec at 44.6V possibly TR626 has failed short c-e so unregulated power (extra ripple, so hum) is being supplied. Suggest diode test TR626, TR628, try in-circuit since looking for a short.
