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Old 9th April 2012, 12:20 PM   #3441
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The good ole Bulb Tester probably wont help in this instance. Better with the series resistor in the B1 supply lead.

What he needs is a slow charging path for C1. The bulb tester will probably still apply the full DC to the B1 faster than C1 can charge.

I don't think he's got a fault. I suspect that he's using a regulated supply that is tripping on over current due to the charging of C1.

If you read back through this thread you will read that we sorted this out for another post earlier.
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Old 9th April 2012, 12:21 PM   #3442
johnm is offline johnm  United Kingdom
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Quote:
Originally Posted by KatieandDad View Post
What kind of PSU are you using ?

Some will not like the high inrush current of C1.

Either try substituting C1 with a smaller say 1000uF cap or try the series resistor as I have mentioned.

C2 is not such a problem because is has R2 in series with it.
Thanks for your reply.

The PSU is a Peter Daniel universal PCB board, which has worked fine for several other projects in the past. I'm using an LM317T set to 24V output. 1000uF 50V cap before & after the regulator. 1uF tantalum caps right next to the input/output legs of the reg as per the datasheets. Just tested the PSU on its own and get a solid 24V output. Used it in the past and its been fine. It's positioned a couple inches away from the B1 board.

Have removed C1 on the B1 PCB and will replace with a 1000uF item and see if it makes a difference. Will also try the series resistor.

As I said though, it's this reading of continuity that I am concerned about. Putting the probes across the (now empty) + and - pads where C1 was I get the meter beeping to show continuity. Surely this isn't good?

- John

Last edited by johnm; 9th April 2012 at 12:23 PM.
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Old 9th April 2012, 12:25 PM   #3443
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If C1 is now out of the board and you are getting continuity that is NOT GOOD.

I would expect something in the order of 5K or so.

A short would indicate that both Q100 and Q101 are short circuit. Or Q200/Q201.
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Old 9th April 2012, 12:26 PM   #3444
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Carefully label and remove Q200 then Q100 testing for a short at both steps.

It is VITAL that they go back where they came from.
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Old 9th April 2012, 12:27 PM   #3445
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If you still have a short with Q100 and Q200 removed then there is problem outwith the JFets.
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Old 9th April 2012, 12:27 PM   #3446
AndrewT is offline AndrewT  Scotland
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Katie's Dad,
you will be surprised at the protection offered by the bulb tester.

Stick in a very low wattage bulb, say 25W and measure the Max DC out from the PSU, during the switch on phase, into a good or bad circuit.
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Old 9th April 2012, 12:28 PM   #3447
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If all is well measure for a short between D and S of both Q100 and Q200.
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Old 9th April 2012, 12:30 PM   #3448
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Quote:
Originally Posted by AndrewT View Post
Katie's Dad,
you will be surprised at the protection offered by the bulb tester.

Stick in a very low wattage bulb, say 25W and measure the Max DC out from the PSU, during the switch on phase, into a good or bad circuit.
I AGREE it does offer GREAT protection. BUT, in this case it wont help with the charging properties of C1.

Anyway, if you are following, I think that there is a deeper seated problem with this B1.

Could be that the JFets have failed. UNUSUAL I know but possible.
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Old 9th April 2012, 12:37 PM   #3449
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I bought 2 lots ie 16 x 2SK170BLs for matching purposes.

This guy is selling genuine articles.

eBay - The UK's Online Marketplace

They are VERY EASY to match but we will cross that bridge when we come to it.
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Old 9th April 2012, 12:48 PM   #3450
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It is highly unlikely that Q101 and/or Q201 have failed.

Unless someone has does something disastorous with the B1.
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