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.
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.
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
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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.
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.
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.
Thanks for the replies guys - much appreciated 
K&D: I too would be surprised if it was the JFETS - I have had this board up and running about 2 years back now when it was just laying on a piece of MDF. Worked fine. Resurrected this project a couple weeks back. Had some better quality 10uF caps so desoldered the old ones and installed these. That's the only change I've made. I guess there's a slight possibility I heat damaged one/more of the JFETS from the desoldering/resoldering... Have plenty of spares however so that's not an issue if it turns out to be the case.
Still don't see how a damaged JFET would cause a short from looking at the PCB. Need to get the schematic open and have a close look again and trace out the possibilities for a short, before taking out any JFETs unnecessarily I guess.
Andrew: The PSU tests fine, and has worked fine plugged into other gear, and I do have a lightbulb tester which I rig up when it's the PSU that's suspect.. In this instance it's most certainly the short I am getting on the DC input of the B1 board (with the PSU disconnected).
- John
K&D: I too would be surprised if it was the JFETS - I have had this board up and running about 2 years back now when it was just laying on a piece of MDF. Worked fine. Resurrected this project a couple weeks back. Had some better quality 10uF caps so desoldered the old ones and installed these. That's the only change I've made. I guess there's a slight possibility I heat damaged one/more of the JFETS from the desoldering/resoldering... Have plenty of spares however so that's not an issue if it turns out to be the case.
Still don't see how a damaged JFET would cause a short from looking at the PCB. Need to get the schematic open and have a close look again and trace out the possibilities for a short, before taking out any JFETs unnecessarily I guess.
Andrew: The PSU tests fine, and has worked fine plugged into other gear, and I do have a lightbulb tester which I rig up when it's the PSU that's suspect.. In this instance it's most certainly the short I am getting on the DC input of the B1 board (with the PSU disconnected).
- John
John,
I agree but there is nothing other than the components that I have already detailed and the JFets between Vcc and 0V.
For Example:-
If D2 the LED was short circuit (unlikely) then you would see R4 = 15K
If D1 were short circuit you might see C2 charging.
R2 and R3 the potential divider for the JFet Gate Bias are unlikely to fail and if they did they would fail open circuit.
C1 has been removed.
That only leaves the JFets or a SHORT across tracks on the PCB.
You have probably created an unintentional short on the 0V plane on the top of the board. Check all solder joints carefully, BOTH sides of the board.
I agree but there is nothing other than the components that I have already detailed and the JFets between Vcc and 0V.
For Example:-
If D2 the LED was short circuit (unlikely) then you would see R4 = 15K
If D1 were short circuit you might see C2 charging.
R2 and R3 the potential divider for the JFet Gate Bias are unlikely to fail and if they did they would fail open circuit.
C1 has been removed.
That only leaves the JFets or a SHORT across tracks on the PCB.
You have probably created an unintentional short on the 0V plane on the top of the board. Check all solder joints carefully, BOTH sides of the board.
K&D: This is getting weirder and weirder.
Just been running continuity tests. If I put the meters probes across R3 (10K) or R2 (10K) the resistance reading jumps about then reads 'OL'. I get a continuity beep which goes after a few seconds. THEN, if I put the probes across the + and - on the DC input of the PCB, I get NO continuity beeping! However if I leave the probes there the resistance reading drops, when it hits around 50-ohms it starts beeping. What's going on there?! Strange!
Could it be something to do with this that Mr Pass mentioned in the B1 PDF:
"By the way, the time constant of R2, R3, and C2 are long enough that it takes
a minute or two for the circuit to reach normal operating values, so don’t get
excited if there’s no sound for a few seconds when you turn it on."
Have I just been a dufus and not given the B1 enough turn-on time?
- John
Just been running continuity tests. If I put the meters probes across R3 (10K) or R2 (10K) the resistance reading jumps about then reads 'OL'. I get a continuity beep which goes after a few seconds. THEN, if I put the probes across the + and - on the DC input of the PCB, I get NO continuity beeping! However if I leave the probes there the resistance reading drops, when it hits around 50-ohms it starts beeping. What's going on there?! Strange!
Could it be something to do with this that Mr Pass mentioned in the B1 PDF:
"By the way, the time constant of R2, R3, and C2 are long enough that it takes
a minute or two for the circuit to reach normal operating values, so don’t get
excited if there’s no sound for a few seconds when you turn it on."
Have I just been a dufus and not given the B1 enough turn-on time?
- John
Left it on for about 20 seconds and nothing happened - didn't want to leave it on longer incase it could damage the PSU. When I turned it off though the LED DID light up for a few seconds though. Had the meters probes in the vacated holes of C1, and I noticed the PSU voltage only started to rise slightly (from approx. 0.235 to 5V) after I'd turned the power off.
Think I'd better do as you suggest and remove Q100 and Q200 and test for shorts rather than try & increase R1?
I don't suppose anyone else could quickly check if they get a continuity/short reading between the + and - on the DC inputs on the B1 PCB?
- John
The resistor will protect against damage, limiting the max current to 24/100 or whatever resistor you are using. 1K = 24mA, nothing will fry at that current.
Q101 and Q201 should be OK. Even if they have full Vcc applied to their Drains they can only pass 7mA or so.
If you have generated a short between C201 or C101 and 0V then the two upperJFets Q200 and/or Q100 could have had full Vcc across them with no current limiting.
With Q200 and Q100 removed check for shorts to 0V at C201 and C101.
Q101 and Q201 should be OK. Even if they have full Vcc applied to their Drains they can only pass 7mA or so.
If you have generated a short between C201 or C101 and 0V then the two upperJFets Q200 and/or Q100 could have had full Vcc across them with no current limiting.
With Q200 and Q100 removed check for shorts to 0V at C201 and C101.
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Right. Will check the parts bin for a 3W 100R resistor to tac over the top of the stock 1R. Think I might have to make a journey to Maplins tomorrow though.
P.S. checked the board for any visual shorts and it's all clean - I'm a neat worker so didn't suspect it would be that anyway. Will get that resistor installed if I find one (if not will get one tomorrow) and if no joy there will check the JFETS.
OK have found a 100R - will fit that now and leave the power on for a minute or so. if no luck there will check Q100/200 out of circuit.
I guess I could lift a leg of R2/R3/D1 first to check they're all OK before going to the trouble of removing those Jfets?