Hi
I need help from the experienced in diagnosing my poorly Leak Delta 30.
It is blowing the 'rect.' fuse on power up.
I have had the amp a few months and it has always had an ugly power on sound, unless I leave it about a minute before switching the speakers in.
The fuse first blew when I inadvertently switched the speakers in almost immediately after power on.
In use the amp had sounded in perfect order with no hum or loss of bass or other symptoms of ailing caps.
I have a spare set of boards from a stereo 70, a pack of the correct fuses, a decent soldering iron, digital multimeter, an understanding of electrical safety, the circuit diagram (which, confusingly for me, piggybacks the delta 70 difference in red) and the ability to recognise components. What I don't have is a complete understanding of how those parts interact to make an amplifier.
So if anyone has suggestions on a course of action, I would welcome them.
The only economic courses of action are fix it myself or buy another.
regards
Ali B
I need help from the experienced in diagnosing my poorly Leak Delta 30.
It is blowing the 'rect.' fuse on power up.
I have had the amp a few months and it has always had an ugly power on sound, unless I leave it about a minute before switching the speakers in.
The fuse first blew when I inadvertently switched the speakers in almost immediately after power on.
In use the amp had sounded in perfect order with no hum or loss of bass or other symptoms of ailing caps.
I have a spare set of boards from a stereo 70, a pack of the correct fuses, a decent soldering iron, digital multimeter, an understanding of electrical safety, the circuit diagram (which, confusingly for me, piggybacks the delta 70 difference in red) and the ability to recognise components. What I don't have is a complete understanding of how those parts interact to make an amplifier.
So if anyone has suggestions on a course of action, I would welcome them.
The only economic courses of action are fix it myself or buy another.
regards
Ali B
If its blowing the 4A fuse from the secondary of the transformer then you need to remove both of the 1.2A fuses feeding the amplifier boards and then retest. That eliminates everything apart from the bridge rectifier and the reservoir caps. If it still blows the fuse then its 50:50 on something this age... but perhaps most probably the bridge that's faulty.
(use a bulb tester... it will save blowing fuses and worse and will allow you to measure voltages (or lack of) safely)
(use a bulb tester... it will save blowing fuses and worse and will allow you to measure voltages (or lack of) safely)
Thanks, yes - that fuse. (Chassis marking says use T3.15A)
Not sure what you mean by bulb tester. I had a quick google but the results didn't show anything I could work out how to use for this.
I'll just go and pop a fresh fuse in and conduct your initial test.
Well it looks like the bridge could be faulty. With it all switched off, try doing a resistance or 'diode' check on the bridge. If you get a low reading across any two pins then its probably faulty.
Also measure across the reservoir cap and see if there is a short there.
A bulb tester is a 60 or 100 watt mains filament bulb wired in series with the mains. If there is a fault drawing excess current, the bulb lights and saves damage. If no fault exists then the cold filament resistance is low enough to allow the amp to work.
Also measure across the reservoir cap and see if there is a short there.
A bulb tester is a 60 or 100 watt mains filament bulb wired in series with the mains. If there is a fault drawing excess current, the bulb lights and saves damage. If no fault exists then the cold filament resistance is low enough to allow the amp to work.
Got odd readings in circuit so I tested the diodes out of circuit.
One is a dead short.
Will replace all with new and test again.
Reservoir not dead short but shows resistance increase the longer the meter is connected.
Normal behaviour?
Thanks for the help so far Mooly!
One is a dead short.
Will replace all with new and test again.
Reservoir not dead short but shows resistance increase the longer the meter is connected.
Normal behaviour?
Thanks for the help so far Mooly!
Yes, the meter is charging the cap, and as it does the resistance reading will increase until it equals the meter's output voltage.
Mike
Absolutely, but if searching, try "bulb limiter" rather than "bulb tester" terms, since the popular use of "bulb tester" naturally refers to something that tests lightbulbs e.g. Christmas lights.
Nope - look here on the forum: http://www.diyaudio.com/forums/equipment-tools/252386-bulb-limiter-testing.html#post3844357
There are even videos on the web but some advice is inappropriate for amplifiers where 60-100W incandescent bulbs prove adequate.
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