Leader / Lonestar AG-2601A audio signal generator

[cowasaki]

I have a Leader LAG-27 and found another audio generator that appeared to be the same model going quite cheap.  I bought it but couldn't find which model of Leader it was.  I then found that it was actually a Lonestar.  Having bought it I replaced a cap and re-soldered several joints.  The generator then worked really well giving me a very clean sine wave.  All the controls work except the "attenuator" control which doesn't do anything.  I took it apart again and checked the front board.  The switch is fine but there was a 470r resistor that was burnt BUT still with it's correct resistance.  I replaced the resistor and re-assembled it.  The generator worked perfectly still except that attenutor switch.  I cannot find a service manual or even a user's manual for it anywhere. 

Does anyone have one?  Anyone any idea where to look now?  I have checked every connection and even component.  There really doesn't appear to be anything obvious.

[bob91343]

Reverse engineer the attenuator.  There is perhaps an open resistor.  Is the output voltage the same as the input to the attenuator?

[cowasaki]

Reverse engineer the attenuator.  There is perhaps an open resistor.  Is the output voltage the same as the input to the attenuator?

There are no bad connections and I've checked every component on the board.  All were within 1% although one 470r was scorched and I've replaced that (it was still in spec)!

[bob91343]

Well it doesn't look to sinister.  The signal to the attenuator goes through resistors to the ouput.  So the output will be less than the signal from the oscillator.  If not, there may be a ground missing or something equally simple.

If the attenuator doesn't do anything, measure (with power off) resistance across output while changing attenuator.

[cowasaki]

Well it doesn't look to sinister.  The signal to the attenuator goes through resistors to the ouput.  So the output will be less than the signal from the oscillator.  If not, there may be a ground missing or something equally simple.

If the attenuator doesn't do anything, measure (with power off) resistance across output while changing attenuator.

I'll have another look.  The front panel board has quite a few holes at one end where there would be components.  I expected that these were for a further model.  When hooked up to the scope the attenuator literally does nothing at all to the signal.  I assumed that it was some kind of voltage divider but all the connections are good that I can see.  Only thing I can do now is reverse engineer the front board which shouldn't be too much of a task and measure, as you mentioned.

[cowasaki]

My next email was from Lodestar....  They are asking for the serial number in order to send the schematic but it doesn't have one.  I've told them this but hopefully I'll get a useful schematic, so I'll leave it till I get a reply.

[enut11]

If you have not fixed it yet, look for a fuse on the pcb. Leader added fuses to the output to protect the generator.
enut11

[bob91343]

Try the same tests with an oscilloscope but this time put a load on the generator, say 600 or 50 Ohms depending on its design.

[cowasaki]

It looks like someone has removed all the components that relate to the attenuator.  I've basically put it back together with no attenuation.  I may look at it again at some point but I have half a dozen valve amplifiers to build and several other things at the moment plus I have a Leader and a digital signal generator so I don't actually need it at the moment.

Thanks everyone.

[enut11]

If you have not fixed it yet, look for a fuse on the pcb. Leader added fuses to the output to protect the generator.
enut11

I might add that the 'fuse'  that Leader used near the output does not look like a fuse,  it is more like a resistor!! I found it by signal tracing backwards from the output.
Another weird fault I found on a Leader oscillator was a faulty wire link, it would not pass current.

[Chris56000]

Hi!

This any good?

If it is this one, please note the h.t. supply voltage is much higher than you'd customarily expect in this type of instrument – it's +42.5V nominal!

Chris Williams

[cowasaki]

Hi!

This any good?

Chris Williams

It looks like the right one.  I'll have a good look and post.  I have a digital gen and another analogue gen but I just like these and snagged it on evil bay for £12 when they normally fetch £50-80.