Help Identifying an old component

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Thanks… I do remember you saying that. I kind of thought that it may well be the culprit, though that’s still uncertain..
But I will do like you’ve said and run a test.
Even so, it feels good to have replaced various bits already with new ones…
So you suggest removing the 106, as in de solder and remove (keep aside)? Now I’ve read your earlier posts I see you suggest to desolder and just pull the legs from the circuit to test..And for the +15v/-15v are you referring to the outputs of the actual psu?
Thanks
Again
Pete
 
You can either just pull the legs out, or remove it entirely - I would suggest it's easier to remove it entirely. The voltages are the outputs from the PSU.
 
Ok…. I removed the 106.. after I put it back together and put some fuses in, I plugged it in and switched it on… pop..
Now I really have not a clue as to how to go further.. I really want to get this thing fixed so I can use the mixer.
So as it stands.. the capacitors have been swapped..
The regulators have been swapped as has the bridge.
After each swap the behaviour remained, so I know that the swaps have been ok so far, just the problem hasn’t been isolated yet..
after removing the 106, the problem still remains..although I have noticed the 48v phantom switch now lights and there is 48v going out.. it’s just the +-15v that is still down..
Would the mc3423 still lead to blowing fuses if the 106 is removed? Isn’t it part of the 106 circuit?
Hmmm starting to wonder what I can do next..
Thanks
Pete
 
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I didn’t put it together in terms of putting the lid on etc and plugging in the mixer. I put the leads back into the board and tested it.. the mixer is well away!
 
It's a VERY simple circuit, there's little to go wrong.

Try removing the 7815 and 7915, and see if it blows the fuses then?.

If it does, then it can only be BR22, or the two 2200uF capacitors, or the two 1uF capacitors in parallel with them - or not a component at all, but a short on the board or something.

Your picture in post #3 shows the board sat on a table, that's how you should be testing it.

I presume you are aware that the 7815/7915 aren't isolated?, it's absolutely essential that the insulating washers and spacers are in place, or the board is sat as in post #3, with the regulators not screwed down.
 
I see…. So I shouldn’t be testing the board with it mounted in the case? It can be hard to plug the power leads in if it’s not. When I have been testing, I have put it in its case and screwed the regulators in with the little screws and spacers.. and just left the lid off to check the fuses reaction
the only thing I haven’t changed yet (aside from the 106) are the 1uf capacitors.. I have some spares of those from the mouser order so I can swap those.
It’s odd… I can see how you mean it’s a simple circuit, which I can see now.. I’m gradually getting my head around it via this investigation.. I now have more fuses on the way so hopefully I’ll be able to do some more testing…
Thanks for all this help… I’d be lost without it!
Pete
 
Don't screw the regulators down, and you could always remove the transformer from the case to give you more range on the wires.

It's far easier to work on things when you have room.

In the meantime (while you wait for fuses), with the regulators still screwed down, check with a meter on low ohms range from the metal tabs of the regulators to the metalwork/heatsink - the 7815 should read low (effectively zero) as the tab is connected to the regulators ground, but the 7915 has the tab connected to the incoming supply, so if it's shorted to ground it will blow the fuse, it should read 'highish', certainly nothing like the 7815.
 
It may not be relevant, but the 47V-rated zener diode (half-way down the board, on the right) has been cooked.
The lower of the two 1N4001 diodes near the 7815 regulator doesn't look very healthy.
 
alec_t said:
It may not be relevant, but the 47V-rated zener diode (half-way down the board, on the right) has been cooked.
The lower of the two 1N4001 diodes near the 7815 regulator doesn't look very healthy.
Click to expand...
The 47V zener is just for the phantom power to feed capacitor mikes, so couldn't blow the fuses - and is actually fed from a completely unfused winding?.

Both the zener and the diodes show a little age, that's all, nothing about them to make me suspicious of failure.
 
And when I last tested it…the phantom power switch lit up when switched on and there was 48v on the board.. so I’m confident the phantom power is working. I’m gonna do the test you suggested tomorrow, I’ve had a GnT so probably best to leave it for today!
 
Nigel, could you explain the test you mentioned regarding testing the 7815/7915 a bit for me? Do I need to screw them to the case? Also should I put the 106 back in order to do the test? And lastly.. is the centre leg the ground? Still learning!
Thanks
Pete
 

If you want to test if the 7915 regulator is shorted to ground, then you need to screw it back in place - but if you have the power supply totally disconnected you can just power it up and see if the fuse blows. The centre pin is ground on the 7815, but not on the 7915. No need to put the 106 back in circuit.
 
Peter Mele said:
Do I need to screw them to the case? Pete
Click to expand...
NOTE - The tab on both 78xx and 79xx regulators is not insulated from the chip. AND - it is different for the two parts.

For a 7815, the tab is GND. But for the 7915, the tab is the ***input***. This means that if both parts are connected to the case without insulation, or with damaged/punctured insulation, the input is shorted to GND. I haven't read the entire thread, but this might be the cause of all those dead fuses.

ak
 
Perhaps check post #29
 
Today is a good day….
I woke up and thought ‘I’m gonna get this working’ so with a box of fuses I went into the workshop..
As I hadn’t yet changed the small 1uf and 10uf capacitors.. I changed those..
And as the 106 removal hadn’t stopped the blowing fuses I put that back.. I did the tests you suggested already and thought to myself… those capacitors are the only thing left.. so with a bit of trepidation I put some fuses in and put the leads back into the board and….. no blowing fuses and leds on and phantom switch all good… I haven’t as yet tried it on the mixer, I’ll test the output lead for the +- 15v first but I’m happy as Larry! So without pre emoting another blown fuse… thank you so much Nigel for your patience with me… I’ve actually fixed it!
 
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