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  1. Paul Ramsbottom

    HP 54510A Power Supply Smelling

    Thanks. I will wait for your suggestions as it is rather over my level of knowledge
  2. Paul Ramsbottom

    HP 54510A Power Supply Smelling

    Replacing the SCR hasn't helped so I have taken it out again. I suppose I could just continue to use it without the protection. It doesn't get a great deal of use and I have replaced many components in the supply side so it is unlikely that it will fail by supplying too great a voltage.
  3. Paul Ramsbottom

    HP 54510A Power Supply Smelling

    Thanks Steve It was an optical illusion. In any case I completely removed the SCR. I have ordered a new one and will report the results. Thank you Paul
  4. Paul Ramsbottom

    HP 54510A Power Supply Smelling

    The 'scope is still working ok without the protection circuit but I am a bit concerned that it is vulnerable to a fault in the power supply. Just a post to ask whether there are any further ideas about finally sorting it out? Thanks Paul
  5. Paul Ramsbottom

    Thurlby PL310 power supply fault

    Apologies for the long delay in replying. In addition to doing the clock I have been laid low for 3 weeks due to s stomach bug. Anyway, the 6 or 7 volts were still appearing on the output at minimum voltage setting. Disconnecting the base of Q2 or that of Q1 reduced the output to around 0.3v...
  6. Paul Ramsbottom

    Thurlby PL310 power supply fault

    Thank you Edd. I replaced the power transistors and that has reduced the output. It is now variable but will not go lower than 6v. It is also affected by turning the current adjusting knob. I have had to put it to one side temporarily as I am overhauling a 1930s longcase triple chime clock...
  7. Paul Ramsbottom

    Thurlby PL310 power supply fault

    Thank you again, Edd. One of the Darlington pair shows open circuit between C and E but the other shows a resistance of 430K when the collector is negative. I disconnected the wires to be sure nothing else in the circuit was affecting it. Q1 is open either way. Does that mean a simple...
  8. Paul Ramsbottom

    Thurlby PL310 power supply fault

    Having had a great deal of help on here over problems with an oscilloscope here is another problem that has just arisen that I hope someone can help with. My son's Thurlby power supply has started to deliver 50v which is lowered slightly by the control but not much. The voltage display shows...
  9. Paul Ramsbottom

    HP 54510A Power Supply Smelling

    I wasn't sure whether I could upload videos onto here so I put them on youtube. They are numbered and follow the pin order on page 6 of the PDF. I think you will be able to get them if you search for MrPaulfrazer on youtube.
  10. Paul Ramsbottom

    HP 54510A Power Supply Smelling

    I suppose that now it is working again I could use it to look at the ripple on its own power supply, Leave it with me and I will try to get some pictures. In the meantime, many thanks for all your help and patience with this problem. Similar thanks to Edd. Paul
  11. Paul Ramsbottom

    HP 54510A Power Supply Smelling

    Might it be one of the zeners or is it likely to be more complex than that? The 'scope doesn't get a lot of use and I am tempted to run it with the protection circuit disabled unless there is something fairly straightforward I can try.
  12. Paul Ramsbottom

    HP 54510A Power Supply Smelling

    Thanks Steve. All the tests show open circuit except Pin 1 Black and Pin 3 Red which shows 593. Paul
  13. Paul Ramsbottom

    HP 54510A Power Supply Smelling

    No problem at all, Steve, I am very grateful for your help. I disconnected two of the legs of the SCR as it wasn't apparent how to disconnect the protection circuit. There is a very quiet clicking when the power supply is not connected to the rest of the 'scope, but it is impossible to tell...
  14. Paul Ramsbottom

    HP 54510A Power Supply Smelling

    After writing the above posting I thought what the hell and decided to connect the main 'scope up with the crowbar disabled and it worked. I would like to get it working properly to be on the safe side. I assume the first place to go would be a new SCR but there are no markings on it as far as...
  15. Paul Ramsbottom

    HP 54510A Power Supply Smelling

    The voltage on C30 and C31 fluctuates but is around 11vwith the link in place. It rises to around 16v with the link removed. The resistance on that rail only rises to around 107 ohms but I assume that is due to R63. As far as I can tell the resistance rises ok on the other rails. I tried...
  16. Paul Ramsbottom

    HP 54510A Power Supply Smelling

    Thanks Steve. I think that the fault is in the pins 17,19,20 rail as the voltage on that is only around 1.5v. The -5.2 is also down to 3.5. The others are near their values but a little low and varying presumably due to the switching on and off of the SMPS. I tried removing C19 whose...
  17. Paul Ramsbottom

    HP 54510A Power Supply Smelling

    Yes the clicking returned when I reconnected that rail. I will go through what has happened so far. Scope working but smell from power supply. Resolved by replacing faulty caps on primary side. Then worked for several hours over several days. New fault. It would run for a few minutes then...
  18. Paul Ramsbottom

    HP 54510A Power Supply Smelling

    I soldered a piece of wire from C30 and 31 to L4 and am back to where I was before I replaced the caps for the second time. It is a 2 layer board so it is difficult to see where the break is. Presumably I disturbed something as I was manipulating it. It was better before I replaced C19 and I...
  19. Paul Ramsbottom

    HP 54510A Power Supply Smelling

    I don't think the reference to 12 on the transformer refers to pin 12. There is the same voltage drop between the positive of the caps and either side of the inductor. I am doing these measurements just with the caps charged and no power supplied. I assume that any break must be between the...
  20. Paul Ramsbottom

    HP 54510A Power Supply Smelling

    There is a 5meg resistance between grid and cathode. All others show open circuit. I cannot understand how I can get a voltage between pin 19 and the positive leads of the caps when they are charged as it seems to me they are directly connected
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