First test...
unplug it all from the mains and put your meter on low ohms, that's the range you would measure something like the 2.2 ohms with.
Put either meter lead on the live pin on the mains plug and (with the amp switched on) see if you can read continuity to either end of C809. It should read short to either one end or the other of the cap.
Now put the meter on the Neutral pin of the plug and see if that reads to cap C809 as well. It will read to the other end of the cap that the first test read too.
unplug it all from the mains and put your meter on low ohms, that's the range you would measure something like the 2.2 ohms with.
Put either meter lead on the live pin on the mains plug and (with the amp switched on) see if you can read continuity to either end of C809. It should read short to either one end or the other of the cap.
Now put the meter on the Neutral pin of the plug and see if that reads to cap C809 as well. It will read to the other end of the cap that the first test read too.
It's probably something daft I've done
OK recapping - mini PSU board connected to IEC inlet. F802 is taken out. Bulb across F801.
PSU board (at C801/805 end) connected to SMPS. SMPSs output not connected back to the PSU board yet...
I think that's it.
On live pin: Yes I get a continuity reading beep (or short) to one end of C809 only (the end which connects to R801).
Doing the same on neutral, I get no continuity beep, but I do get a reading of some 70-ohms to the other end of C809.
OK... so that appears to show a break in the "other" side.
The end of C809 that doesn't have continuity.
First of all read from there to the fuse... refer to the circuit... and of course it should read. Then follow from there to the switch, maybe that is duff on one pole. If so it will read up to the switch but not beyond and back to the plug.
The end of C809 that doesn't have continuity.
First of all read from there to the fuse... refer to the circuit... and of course it should read. Then follow from there to the switch, maybe that is duff on one pole. If so it will read up to the switch but not beyond and back to the plug.
There's no fuse fitted - instead we have the bulb...
Shall I take out the bulb and try with the fuse in place?
Of course, my fault
Does the side of the fuseholder (F801) that goes to the switch read short to the "neutral" pin of the plug ?
yep. No problem there.
Just to make the picture clearer, on the IEC inlet Live is brown, and neutral is yellow.
Both of these run direct to the mains switch on the front of the amp.
From the mains switch, we get orange (live) and white (neutral) returns back to the AC input of the smaller PSU board. The white goes to the input end of either fuse. The orange to one end of C809, R801, and also the relay.
Hope that helps in some way?
Both of these run direct to the mains switch on the front of the amp.
From the mains switch, we get orange (live) and white (neutral) returns back to the AC input of the smaller PSU board. The white goes to the input end of either fuse. The orange to one end of C809, R801, and also the relay.
Hope that helps in some way?
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OK, so there has to be 240vac across C809. Just check it with it all plugged in and switched on.
Remember to put the meter on AC volts for this.
Ok-dokey
Yep checked and confirmed.
Mooly, before I do that, I need to ask about safety. To cut a long story short, I'm currently at home and the folks are expressing concern this morning about me sliping and meeting my maker haha! As I'm suffering from an illness called M.E. which can affect ones concentration and sometimes means the hands aren't so steady, I take their point. Can something as simple as wearing rubber gloves to offer insulation against touching something live help when making high DC measurements?
If I was living on my own again I'd just do it, but now I have the parental eyes upon me
Thanks.
- John
If I was living on my own again I'd just do it, but now I have the parental eyes upon me
Thanks.
- John
Yes dry rubber gloves certainly would stop any risk.
The biggest problem might be holding leads steady when measuring in a confined area.
If that's a problem then perhaps rigging the meter leads up to a block connector and from there have two wires you can quickly solder to the points we need to measure.
You could perhaps do that with the negative lead as all measurements now are from the negative end of C805.
A good safety rule when working on anything is to only use one hand. That way you can never get a shock across you.
The biggest problem might be holding leads steady when measuring in a confined area.
If that's a problem then perhaps rigging the meter leads up to a block connector and from there have two wires you can quickly solder to the points we need to measure.
You could perhaps do that with the negative lead as all measurements now are from the negative end of C805.
A good safety rule when working on anything is to only use one hand. That way you can never get a shock across you.
Thanks for that advice Mooly 
I'll get some marigalds or something later today then. I hope they do them in blue haha!
I think if I could have one meter probe anchored firmly to the negative side (when there's enough component lead to grip onto that is) and only used one hand (the right I've been told) to make the measurements I guess that would be safer. Something else I need to get today then is a decent pair of croc. clip meter probes.
So the measurements I need to take at present can be done - as you suggest - with the negative probe clipped onto the - side of C805 then?
I'll get some marigalds or something later today then. I hope they do them in blue haha!
I think if I could have one meter probe anchored firmly to the negative side (when there's enough component lead to grip onto that is) and only used one hand (the right I've been told) to make the measurements I guess that would be safer. Something else I need to get today then is a decent pair of croc. clip meter probes.
So the measurements I need to take at present can be done - as you suggest - with the negative probe clipped onto the - side of C805 then?
Croc clips can be risky... they have a habit of flirting off shorting things out.
It's what ever you feel happiest with. At the moment there are only two checks to do.
The voltage across the series caps, and that has to be OK if there is 240vac entering the bridge. The same voltage should appear across C601.
The other check is that DC voltage across D601.
Shall we take a break there... I'll look in later
It's what ever you feel happiest with. At the moment there are only two checks to do.
The voltage across the series caps, and that has to be OK if there is 240vac entering the bridge. The same voltage should appear across C601.
The other check is that DC voltage across D601.
Shall we take a break there... I'll look in later