XL500 sample timing

[porkluvr]

... you know that by now I am not an electronics expert...

If you use an oscilloscope then you can step-by step analyze what is going on. That is how you can become an expert.

If you don't use a scope but instead shotgun components, you'll never know what has happened. You will be shooting in the dark and stand a very good chance of doing further harm.

[Micheal]

There is no voltage at the coil connector

[homefire]

Follow it back.

Is the Drive Transistor being fired?

Is it getting power?

[Qiaozhi]

There is no voltage at the coil connector

It appears that you have a problem either with the TX circuit or the coil. First check the continuity of the coil. If that's ok, then monitor pin3 of the 555 timer to see if it's oscillating.

[homefire]

Ok!

First thing I would do would be check the following.

1. Did the coil swamp and short?

2. Coil wires on that board is funky and can short most easy.

3. Check drive transitor for power both ends and Drive.

4. Is the 555 doing it's thing?

[Micheal]

I have checked the coil and it is fine ...pin3 of the lm555 is showing a constant 5.4volts without any variation in voltage

[Micheal]

which one is the drive transistor is it the 79L05

[Qiaozhi]

I have checked the coil and it is fine ...pin3 of the lm555 is showing a constant 5.4volts without any variation in voltage

Are you using an oscilloscope to do the measurements, or a voltmeter?

[Micheal]

I am using a voltmeter...and thats all I have.
after checking all the above things and some resoldering ...all I have is sometimes it will detect a pliers at 1cm and the tone seems to be steady now and not dropping off but very weak detection...There is voltage at the coil connection(sorry right now I cant remember I think it was 0.18volts and stays at that voltage constantly even when you turn the sensitivity up or down),Basically it sounds ok now with very weak detection.

[Qiaozhi]

I am using a voltmeter...and thats all I have.
after checking all the above things and some resoldering ...all I have is sometimes it will detect a pliers at 1cm and the tone seems to be steady now and not dropping off but very weak detection...There is voltage at the coil connection(sorry right now I cant remember I think it was 0.18volts and stays at that voltage constantly even when you turn the sensitivity up or down),Basically it sounds ok now with very weak detection.

Does your voltmeter have the ability to measure frequency?

[Micheal]

Unfortunately it doesnt have frequency function...so I will get one that has the frequenct function

[Qiaozhi]

Unfortunately it doesnt have frequency function...so I will get one that has the frequenct function

It would be an excellent investment to buy an oscilloscope, if you have the money. Otherwise, a meter with a frequency function will be useful. You can then use it to check if the 555 is oscillating.

My suspicion is that the transmitter is generating very weak pulses. That's why it works, but very poorly. The output transistors are most likely kaput.

[Micheal]

Thanks for your help guys...please bare with me ,I dont have a scope and I dont know how to use one .Thats why I try to use this elimination method to fix things and a lot of the times it works ,Which ones are the output transistors are they the 3906 little buggers becuase I have replaced all of them I think there was 5 and the 79L05 and all the 2 black and all the blue capacitors in the picture I have tried a new lm555 I am trying hard to trace it down but i just cant find it ...I have attached a picture of the board which one is it in the picture

[Qiaozhi]

Thanks for your help guys...please bare with me ,I dont have a scope and I dont know how to use one .Thats why I try to use this elimination method to fix things and a lot of the times it works ,Which ones are the output transistors are they the 3906 little buggers becuase I have replaced all of them I think there was 5 and the 79L05 and all the 2 black and all the blue capacitors in the picture I have tried a new lm555 I am trying hard to trace it down but i just cant find it ...I have attached a picture of the board which one is it in the picture

The TX transistors are shown in the attached schematic, and the component layout. I would try replacing these first. Please also check that you have the transistors in the right way round. This may seem obvious, but the pinout depends on the country of manufacture, even for the same part number.

[Micheal]

the schematics you have drawn the parts on is different to my xl500 if you have a look at my photo.The 3055 in mine is a RFP8N18L and on mine there is no MPSU60(I couldnt find anywhere on the net a schematic for this version of the xl500 )