The voltage drop across the LED won't tell you much as it's fairly constant for any current. Measure the voltage across R18 and R118. This will give you the current through the LEDs which should be the same. The only other way that LED 102 could be getting more current is from leakage through Q108 base/collector which is unlikely. Finally you could lift one leg of the LEDs and insert a meter to compare the currents directly.
Or not bother if it's working well.
Or not bother if it's working well.
Hi spandrel
Will have a look but all transistors and semiconductors were matched to each other (L/R channels) and hence the matched Leds.
The Q108, R118, C111 and Led 102 all measure fine and are brand new
This is my "pet" amplifier and I want to get it right
Will have a look but all transistors and semiconductors were matched to each other (L/R channels) and hence the matched Leds.
The Q108, R118, C111 and Led 102 all measure fine and are brand new
This is my "pet" amplifier and I want to get it right
Oh crap
Don't know what happened the amp is in protection mode (all 4 leds on) but relay will not latch.
I did that and also swapped then around and nothing the issue is on that side of the circuit
Oh well sh*t happens
Don't know what happened the amp is in protection mode (all 4 leds on) but relay will not latch.
I did that and also swapped then around and nothing the issue is on that side of the circuit
Oh well sh*t happens
It's driving me nuts
Was fine yesterday and today plugged it in to test the Dual 701 I'm restoring and nothing just dead funny thing is it didn't blow any fuses and all leds are lit
Checked the protection circuit and everything is OK
Tomorrow is another day...
Was fine yesterday and today plugged it in to test the Dual 701 I'm restoring and nothing just dead funny thing is it didn't blow any fuses and all leds are lit
Checked the protection circuit and everything is OK
Tomorrow is another day...
Back to this A3i...
Still same problem left channel looks fine but has to idle current at all (amp in protection mode)
Right channel same thing (no idle current) and LEDs are not bright has the ones on the left channel.
Amplifier tested with bulb tester in place
Any ideas before I plug it strait to the wall ?
PS: The A3i must have been very reliable this last year no one posted asking for help since August last year.
Still same problem left channel looks fine but has to idle current at all (amp in protection mode)
Right channel same thing (no idle current) and LEDs are not bright has the ones on the left channel.
Amplifier tested with bulb tester in place
Any ideas before I plug it strait to the wall ?
PS: The A3i must have been very reliable this last year no one posted asking for help since August last year.
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If you can find one, try a higher rated bulb in your DBT before you blast it with full voltage or start taking more invasive action. It may be a voltage threshold problem and hence a further clue to what the problem actually is.
The A3i uses an R core transformer, if your Dim bulb tester has a 100 watt bulb it will be glowing and limiting the current to the Amplifier.
Please check the FET(s) Q7 and Q107 remove them from circuit, you will most likely see they are reading diode junction on the tester rather than N channel FET, Q8 and Q108 should be replaced if they have not been as over time due to running hot they deteriorate and guidance is to replace them. Also if you look at the circuit board a round the area of Q1,Q2,Q3,4 and Q101,Q102,Q103, Q104, you may see what looks to be a dried liquid and there is a odd smell on older A3is those transistors physically start to break down.Its better to block change them out as they are inexpensive. Clean the top of the board before refitting the new devices, I would also test out of circuit the gain of the BD139 and BD140 driver transistors I have seen many instances where the gain is as low as 3 to 5 if they reading very low change them out. Also check the solder side of the board for dry joints particularly around the components that generate heat Q7/107 Q8/108 and the green LEDs, I understand you have already replaced them.
Please check the FET(s) Q7 and Q107 remove them from circuit, you will most likely see they are reading diode junction on the tester rather than N channel FET, Q8 and Q108 should be replaced if they have not been as over time due to running hot they deteriorate and guidance is to replace them. Also if you look at the circuit board a round the area of Q1,Q2,Q3,4 and Q101,Q102,Q103, Q104, you may see what looks to be a dried liquid and there is a odd smell on older A3is those transistors physically start to break down.Its better to block change them out as they are inexpensive. Clean the top of the board before refitting the new devices, I would also test out of circuit the gain of the BD139 and BD140 driver transistors I have seen many instances where the gain is as low as 3 to 5 if they reading very low change them out. Also check the solder side of the board for dry joints particularly around the components that generate heat Q7/107 Q8/108 and the green LEDs, I understand you have already replaced them.
To Ian Finch, will have to stick to the 60W one been to 3 stores and only LED ones available.
To audio service, this amp was serviced around 2 years ago by myself and all usual culprits were replaced and/or upgraded as per Alex (Xpro) instructions, right now it power up and all 4 LEDs light up but like I mentioned the ones on the right channel are not as bright compared to the left channel and is stuck in protection mode.
All transistors (including output ones) where tested of circuit with multimeter and transistor tester and all are within spec.
Going to start lifting resistors and diodes to see if something is amiss.
To audio service, this amp was serviced around 2 years ago by myself and all usual culprits were replaced and/or upgraded as per Alex (Xpro) instructions, right now it power up and all 4 LEDs light up but like I mentioned the ones on the right channel are not as bright compared to the left channel and is stuck in protection mode.
All transistors (including output ones) where tested of circuit with multimeter and transistor tester and all are within spec.
Going to start lifting resistors and diodes to see if something is amiss.
You advised that your powering the Amplifier via the dim bulb tester, correct me if that's not the case.
Also if you measure across the bias trimmers you should have approximately 1.3 volts.
Also if you measure across the bias trimmers you should have approximately 1.3 volts.
Yes I powered it up through the dim bulb tester with a 60W bulb.
Will have to check that but I have other thing on my plate and this one is not urgent I have around 10 amplifiers here at home so I will take my time with it.
Will have to check that but I have other thing on my plate and this one is not urgent I have around 10 amplifiers here at home so I will take my time with it.
Hi guys, I new on here as I just got a A3i Amplifier.
I've got back into Audio/electronics after a really long time and it is good to be back!
I got myself an A3i last week to play some old vinyls as it has a phono stage built in. It worked good until yesterday when I smelled some 'hot' electronics. After turning it off and opening the case, I saw that everything looked fine except that there was no heatsink where there was supposed to be one and from where the heat was coming from.
I googled up information on the A3i, found some schematics and pics online and from what I saw, was that my A3i had been modded and looked quite different on the inside from what I saw in the schematics and pics.
The amp is quite ok and sounds good but starts to get hot once the volume setting is turned up past the 12 0'clock position and gets the speakers jarring ( Celestion Ditton 130, 8 ohms 70 watts) when the volume control gets to the 9 0'clock position.
I would appreciate it if someone could help me out with letting me know as to what exactly do I have, here?
Cheers!
I've got back into Audio/electronics after a really long time and it is good to be back!
I got myself an A3i last week to play some old vinyls as it has a phono stage built in. It worked good until yesterday when I smelled some 'hot' electronics. After turning it off and opening the case, I saw that everything looked fine except that there was no heatsink where there was supposed to be one and from where the heat was coming from.
I googled up information on the A3i, found some schematics and pics online and from what I saw, was that my A3i had been modded and looked quite different on the inside from what I saw in the schematics and pics.
The amp is quite ok and sounds good but starts to get hot once the volume setting is turned up past the 12 0'clock position and gets the speakers jarring ( Celestion Ditton 130, 8 ohms 70 watts) when the volume control gets to the 9 0'clock position.
I would appreciate it if someone could help me out with letting me know as to what exactly do I have, here?
Cheers!
Attachments
That looks to me as though someone has ripped out the original amp boards and fitted boards from China.
If that was not the description I would look to getting your money back.
If that was not the description I would look to getting your money back.
Holly crap...
Even the transformer is the wrong one.
Can I ask how much you paid for it ?
Even the transformer is the wrong one.
Can I ask how much you paid for it ?
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Hi hoping someone can help me out I have an a1 revision 1.5 with the tip3055/2955 op transistors, the right hand drive transistor has an open base unfortunately there don’t appear to be any markings on it. If anyone has the correct circuit diagram or know what the transistor is I will be very grateful Antony
Look for the A1 MK1 thread in this forum for help but i can tell you right now that there is no manual or schematic available for the early A1
Post some pictures I may be persuaded to open one of my A1.
Look here: Cambridge audio a1 mk1 not powering on.
Post some pictures I may be persuaded to open one of my A1.
Look here: Cambridge audio a1 mk1 not powering on.
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