Along with the parts I also had already ordered a chasing lights kit to learn to solder! But a very fair point.
However looking again last night I think I have bought the wrong IRC540's. Maybe you could point me again in the right direction.
What came up on the internet on a search for the IRF540 (purely by looking at the physical case of the component, looks on the schematic as parts Z201 and Z202 listed in the service manual as "IC vreg pos and neg", not the Q1 "Trans Pwr Mosfet IRF540" I'm looking for.
To complicate matters I cant even find Q1 and 2 on the board..just Q3,4,5,6,7,8,9 ect. Some more research needed I think! On the plus side I have built the lamp tester thingy.
However looking again last night I think I have bought the wrong IRC540's. Maybe you could point me again in the right direction.
What came up on the internet on a search for the IRF540 (purely by looking at the physical case of the component, looks on the schematic as parts Z201 and Z202 listed in the service manual as "IC vreg pos and neg", not the Q1 "Trans Pwr Mosfet IRF540" I'm looking for.
To complicate matters I cant even find Q1 and 2 on the board..just Q3,4,5,6,7,8,9 ect. Some more research needed I think! On the plus side I have built the lamp tester thingy.
Don't quite understand what you mean...
The output FET's (which will be on the main heatsink) should be replaced like for like. Where do the voltage regulators come into it all ?
Generally speaking unless you have an exact service manual for the exact variant you are working on then component references and so on can all be different.
The output FET's (which will be on the main heatsink) should be replaced like for like. Where do the voltage regulators come into it all ?
Generally speaking unless you have an exact service manual for the exact variant you are working on then component references and so on can all be different.
Either of these should be fine,
CPC - Over 100, 000 products from one of the worlds leading distributors of electronic and related products. | CPC
CPC - Over 100, 000 products from one of the worlds leading distributors of electronic and related products. | CPC
Thanks Mooly, I really appreciate your help.
I have the service manual for the Arcam Alpha One/7/8R/8P. Mine is the 8R so I think i'm ok.
I will look again tonight, I got confused with the voltage regulators as they look similar in physical appearance to the mosfets from what I can find on the internet to look at and from the product pages of the component manufacteurs. I thought I had been incorrect in identifying them as there were only two and i'm expecting to find four. The heatsink connection should make identifying easier.
Please accept my "newbie-mess" in this, I know what i'm saying probably sounds pretty stupid to anyone who has done this for anytime at all.
I have the service manual for the Arcam Alpha One/7/8R/8P. Mine is the 8R so I think i'm ok.
I will look again tonight, I got confused with the voltage regulators as they look similar in physical appearance to the mosfets from what I can find on the internet to look at and from the product pages of the component manufacteurs. I thought I had been incorrect in identifying them as there were only two and i'm expecting to find four. The heatsink connection should make identifying easier.
Please accept my "newbie-mess" in this, I know what i'm saying probably sounds pretty stupid to anyone who has done this for anytime at all.
schematicse manual for arcam 8
Hi I hope you don't mind me asking if its possible to have a copy of the above schematics ,if you still have them as I've just got a Arcam 8 to try and repair for a friend it's burnt the Pcb very badly and though i can work out most of the circuit im not 100% on certain values regards john(celestica)
Hi I hope you don't mind me asking if its possible to have a copy of the above schematics ,if you still have them as I've just got a Arcam 8 to try and repair for a friend it's burnt the Pcb very badly and though i can work out most of the circuit im not 100% on certain values regards john(celestica)
I've got an issue with arcam alpha 7 amp which has same pcb.
So while unit was turned on i managed to short speaker outputs in one of the channels. Relay switched off the speaker out, then it came back to normal. Amp is working but there are distortions in right channel, left channel is ok.
Here are the measurements
180mv tp22
2.9v tp23
-2.5v tp24
1.8mv between tp26 tp27.
r110 and r111 are now 380ohm instead of 470ohm
Should i replace all 4 irf540 for irf540pbf by IR? What should i do about it?
So while unit was turned on i managed to short speaker outputs in one of the channels. Relay switched off the speaker out, then it came back to normal. Amp is working but there are distortions in right channel, left channel is ok.
Here are the measurements
180mv tp22
2.9v tp23
-2.5v tp24
1.8mv between tp26 tp27.
r110 and r111 are now 380ohm instead of 470ohm
Should i replace all 4 irf540 for irf540pbf by IR? What should i do about it?
You can't read resistances in circuit (which it sounds like you are doing because resistors don't fail by going low in value).
If its the same amp as in this thread then follow the fault finding procedures outlined earlier in the thread 🙂
Always use the bulb tester until you are sure its fixed. Also, the FET's would normally fail by going short circuit so check those and also that the 0.22 ohm resistors in the source of Q2 are OK.
If its the same amp as in this thread then follow the fault finding procedures outlined earlier in the thread 🙂
Always use the bulb tester until you are sure its fixed. Also, the FET's would normally fail by going short circuit so check those and also that the 0.22 ohm resistors in the source of Q2 are OK.
Alpha 8P help
Dear Mooly, I have an ALPHA 8P, some years ago it blow its fuse and the spare. I contacted ARCAM to see if they could repair it, at the time I felt it was too much. Recently I felt I should take a look to fix it myself. Having read your thread I figured it was worth a try.
I have replaced IRF540's with IRF 540PBF's, on removal of the old one's I tested them using the simple diode test method on a digital DMM found on Youtube, all were fine. Also replaced Q(10)3, Q(10)4, Q(10)5 and Q14 & Q114 in all 8 transistors. (did not both testing)
Did the light bulb protection, switched on and the bulb just glowed brightly. As nothing else happened for a couple second (bulb still glowing) I shut off the power. Checked my work and tried again leaving it on a bit longer still no joy 🙁
I'm wondering what to do next, having spent £14 with Farnell it would be nice to get it working again!
Dear Mooly, I have an ALPHA 8P, some years ago it blow its fuse and the spare. I contacted ARCAM to see if they could repair it, at the time I felt it was too much. Recently I felt I should take a look to fix it myself. Having read your thread I figured it was worth a try.
I have replaced IRF540's with IRF 540PBF's, on removal of the old one's I tested them using the simple diode test method on a digital DMM found on Youtube, all were fine. Also replaced Q(10)3, Q(10)4, Q(10)5 and Q14 & Q114 in all 8 transistors. (did not both testing)
Did the light bulb protection, switched on and the bulb just glowed brightly. As nothing else happened for a couple second (bulb still glowing) I shut off the power. Checked my work and tried again leaving it on a bit longer still no joy 🙁
I'm wondering what to do next, having spent £14 with Farnell it would be nice to get it working again!
Hi Joe.
Replacing a lot of parts in hope probably isn't the best way to go about something like this 🙂
In the first instance you need to determine whether the bulb lighting is a problem with the power supply or a problem with the circuitry in one or both channels.
It would be worth linking out (just short all three pins together) Q115 on both channels. Then see if the bulb is still bright.
If it is then you need to disable both channel output stages. Removing Q104 and Q105 for both channels looks as though it should accomplish that.
Replacing a lot of parts in hope probably isn't the best way to go about something like this 🙂
In the first instance you need to determine whether the bulb lighting is a problem with the power supply or a problem with the circuitry in one or both channels.
It would be worth linking out (just short all three pins together) Q115 on both channels. Then see if the bulb is still bright.
If it is then you need to disable both channel output stages. Removing Q104 and Q105 for both channels looks as though it should accomplish that.
Hi Mooly,
Good point 😛, I was being hopeful I guess 😱!
Just to be clear (and so I don't create more issues) by shorting out, do you mean solder across all the terminal with a small wire for Q115 (RH channel) and at the same time do the same to Q15 (LH Channel)?
Forgot to mention I have turned down both RV1 and RV101 fully anticlockwise, I had the DMM across the R1 to measure the mV output but nothing there, expect this due to the bulb inhibiting the circuit.
Thanks for the swift reply, really appreciate this.
Good point 😛, I was being hopeful I guess 😱!
Just to be clear (and so I don't create more issues) by shorting out, do you mean solder across all the terminal with a small wire for Q115 (RH channel) and at the same time do the same to Q15 (LH Channel)?
Forgot to mention I have turned down both RV1 and RV101 fully anticlockwise, I had the DMM across the R1 to measure the mV output but nothing there, expect this due to the bulb inhibiting the circuit.
Thanks for the swift reply, really appreciate this.
Yes, shorting that transistor will force the bias current to its lowest possible value. You actually only need short collector to emitter but if you weren't sure of the pinouts then all three is guaranteed to do the same.
If you turned the presets to minimum bias already then I don't hope much hope that this step will prove anything but having said that it removes any question mark over that stage.
And yes, do both channels the same.
If you turned the presets to minimum bias already then I don't hope much hope that this step will prove anything but having said that it removes any question mark over that stage.
And yes, do both channels the same.
Hi Mooly,
Have shorted out Q5 and Q115, Lamp - ON
Removed Q4,Q5 and Q104, Q105, Lamp - ON
I have had a good look at the components and the circuit board but can not see anything which has obviously failed. None of the caps are domed.
So what next? Should I re-solder the 4 transistors again. Thanks!
Have shorted out Q5 and Q115, Lamp - ON
Removed Q4,Q5 and Q104, Q105, Lamp - ON
I have had a good look at the components and the circuit board but can not see anything which has obviously failed. None of the caps are domed.
So what next? Should I re-solder the 4 transistors again. Thanks!
Leave the parts shorted and unsoldered until we find the reason for the excess current draw.
At this stage there are only two tests to do...
1/ Have you checked that the bridge rectifier is OK (that's the big diodes in the power supply, D201/2/3 and 4).
2/ Carefully isolate (unsolder) the 'Drain' (middle leg) of all four power FET's.
One or other of those two steps should cause the bulb to go out.
At this stage there are only two tests to do...
1/ Have you checked that the bridge rectifier is OK (that's the big diodes in the power supply, D201/2/3 and 4).
2/ Carefully isolate (unsolder) the 'Drain' (middle leg) of all four power FET's.
One or other of those two steps should cause the bulb to go out.
And I should have asked this at the start. With the amp OFF, can you measure a short across either rail. That's the plus 37 and minus 37 rails measured to ground.
Have desolder one side (neg side) of all the big diodes, D203 is a dead short - it buzzed, all others appear OK as they read 396 to 392 on the DMM in diode test mode.
Not sure I follow you last comment where to take the readings from, will need to bring up the circuit diagram I guess to figure out the +/- 37v rail locations. Btw the amp is out of its case and not plugged in. Should this test be done with power lead I but amp not switched on?
Not sure I follow you last comment where to take the readings from, will need to bring up the circuit diagram I guess to figure out the +/- 37v rail locations. Btw the amp is out of its case and not plugged in. Should this test be done with power lead I but amp not switched on?
Tested the diodes, have desolder their negative sides and tested them with the DMM diode test, D203 is a dead short - it buzzes across it, the others read 395 to 392 so think they are OK.
The Amp is outside of its case with out the power lead in. I will need to look up the circuit diagram to figure out the -/+ 37 rails unless there is an easy test point you can suggest?
The Amp is outside of its case with out the power lead in. I will need to look up the circuit diagram to figure out the -/+ 37 rails unless there is an easy test point you can suggest?
The diode being short might be the only problem. Replace that and test the amp again (still with the bulb tester and still with those transistors linked out and removed. You can leave isolating the FET's for now.
Hopefully that might be the only problem.
Maplin have 1N5408's which are higher rated voltage wise. £0.09 each which is remarkably cheap for them. You can check local store stock from the screen.
1N5408 3A Silicon Rectifier | Maplin
The -/+37 volt rails are the main power supplies derived from these diodes.
Edit... and replace all four diodes.
Hopefully that might be the only problem.
Maplin have 1N5408's which are higher rated voltage wise. £0.09 each which is remarkably cheap for them. You can check local store stock from the screen.
1N5408 3A Silicon Rectifier | Maplin
The -/+37 volt rails are the main power supplies derived from these diodes.
Edit... and replace all four diodes.
Hi Mooly,
Just replaced all 4 rectifier diodes, left transistors as you suggested, bulb in place and turned on... bulb glowed low for a few seconds then went out as inrush current settled. Orange led switched to green when relay activated and the amp looked OK. So I think this fix is a success. Before I replace the 4 resistors and remove the shorts across Q15 and Q115 should I do anything else?
Just replaced all 4 rectifier diodes, left transistors as you suggested, bulb in place and turned on... bulb glowed low for a few seconds then went out as inrush current settled. Orange led switched to green when relay activated and the amp looked OK. So I think this fix is a success. Before I replace the 4 resistors and remove the shorts across Q15 and Q115 should I do anything else?
That's all sounding promising.
Refit the removed transistors (we didn't pull any resistors did we ?), but yes, rebuild it all back making sure you get the transistor placement correct.
I'm wondering whether its best to do one channel at a time... up to you 🙂 In either case leave the short across Q5/115 until we are sure its all fixed and keep using the bulb tester until its done.
Also make sure you allow sufficient time for the main power supply caps to discharge before beginning soldering. Give it a couple minutes.
Hopefully with all the parts fitted the amp should work and play music. Don't turn it up loud with the bulb tester fitted because the voltage rails will collapse suddenly and the amp might do unpredictable things. Just make sure it seems OK. There may be some audible distortion because the bias is at zero (the shorted transistor).
Only when we are sure its OK do we remove the short and see if the bias current adjusts. Make sure that the preset is turned to the position that gives it maximum resistance. In other words it needs to be like a 10k resistor and not a short. That condition gives minimum bias current.
Good luck... it will be tomorrow before I look in again.
If your not sure then wait and ask 🙂
Refit the removed transistors (we didn't pull any resistors did we ?), but yes, rebuild it all back making sure you get the transistor placement correct.
I'm wondering whether its best to do one channel at a time... up to you 🙂 In either case leave the short across Q5/115 until we are sure its all fixed and keep using the bulb tester until its done.
Also make sure you allow sufficient time for the main power supply caps to discharge before beginning soldering. Give it a couple minutes.
Hopefully with all the parts fitted the amp should work and play music. Don't turn it up loud with the bulb tester fitted because the voltage rails will collapse suddenly and the amp might do unpredictable things. Just make sure it seems OK. There may be some audible distortion because the bias is at zero (the shorted transistor).
Only when we are sure its OK do we remove the short and see if the bias current adjusts. Make sure that the preset is turned to the position that gives it maximum resistance. In other words it needs to be like a 10k resistor and not a short. That condition gives minimum bias current.
Good luck... it will be tomorrow before I look in again.
If your not sure then wait and ask 🙂