If the problem is not the pad grounded but the lead of the 7915 IC not (bad solder joint) then you need to make a splice wire from the lead to the nearest ground. There is on the schematic a ground at the middle terminal of Jblob the voltage feed connector, and one terminal of each filter capacitor is grounded.
If the ground terminal of a regulator has been open for years, could be the unregulated voltage exceeded the rating of an op amp and blew it up. Ceramic Caps are usually minimum 50 v rated, they are less likely to short, but local e-caps to the op amps could be 25 v rated and short. Or any other component loaded on the +-15 v supply.
If the ground terminal of a regulator has been open for years, could be the unregulated voltage exceeded the rating of an op amp and blew it up. Ceramic Caps are usually minimum 50 v rated, they are less likely to short, but local e-caps to the op amps could be 25 v rated and short. Or any other component loaded on the +-15 v supply.
Well, i was wrong again 'cause i assumed the center leg as ground like the 7815. It's the left leg, and there are no problems with wiring etc.
Probably the late hour fooled me, i don't know...
Tried to measure DC input on both of them, the e caps are still desoldered but i measure 0.3v on 7815 and 0 v on the 7915. Ok, i've no filter caps so i shouldn't expect a good DC signal, but... Isn't it too low anyway?
I think i'replace the e caps anyway, even if the measure fine. I got the replacements, so...
Probably the late hour fooled me, i don't know...
Tried to measure DC input on both of them, the e caps are still desoldered but i measure 0.3v on 7815 and 0 v on the 7915. Ok, i've no filter caps so i shouldn't expect a good DC signal, but... Isn't it too low anyway?
I think i'replace the e caps anyway, even if the measure fine. I got the replacements, so...
my eyes are still good for an old guy but even in my younger days with better peepers i couldn't spot cracked solder joints without a magnifying glass.so no leaky or shorted caps either...(i guess you checked them all right)
Would be hard to have 15 v drop on protection resistors if the 17 vac wasn't there.
When you pull the plug from the power board to the op amp board, does the 15 v drop on the protection resistors go to zero?
Mark it and don't put it back backwards (if that is physically possible).
When you pull the plug from the power board to the op amp board, does the 15 v drop on the protection resistors go to zero?
Mark it and don't put it back backwards (if that is physically possible).
Hey, yes the transformer voktage is present and no the voltage drop at the protection resostances remains at +- 15 v...
sorry as far is i knew he was doing all this without the preamp board plugged in but who knows...
and i don't think he's measuring "across" the resistor itself but with respect to ground as in common of the meter to gnd and the meter plus lead to the resistor but again i ain't there...
Oh boy, i was measuring across it. Why not, after all?
In fact, with the black lead at the input connector ground and the positive lead on any protection resistor i got like 0.8 Vac.. Across it 16 Vac. Isn't it a valid element that the problem should be after the resistors?
In fact, with the black lead at the input connector ground and the positive lead on any protection resistor i got like 0.8 Vac.. Across it 16 Vac. Isn't it a valid element that the problem should be after the resistors?
Yes, if your getting 16 Vac across the protection resistors, the problem is after the protection resistors.
So you are getting no DC out the pins of connector to the op amp board with the power on.
Check the power board again, remove one end of the protection resistors, then see if you get <10 ohms between +15 and -15 out pins. Also check that the protections resistors are actually about 1 kohms.
Maybe if you're dropping 16 vAC across the protection resistors with the op amp board disconnected, and the board is shorted, it is time for a whole new board.
I've made +- DC power supplies on little pieces of insulation board. I screw them to the case with a standoff made of 1/4 air tubing and a #6 machine screw.
You take some board, like polycarbonate plastic window glazing or nema C laminate (canvas laminate board is what I use), drill some holes, run some wire with hooks bent in the end. Fly the 16 vac out the resistor holes, back in somewhere near the output connector. If you can't get the output connector not shorted, you pull the pins out, or splice into the three power wires with solder. You drill #19 holes for the mount screw and #27 holes for the wires. I could do this in about 2 hours.
So you are getting no DC out the pins of connector to the op amp board with the power on.
Check the power board again, remove one end of the protection resistors, then see if you get <10 ohms between +15 and -15 out pins. Also check that the protections resistors are actually about 1 kohms.
Maybe if you're dropping 16 vAC across the protection resistors with the op amp board disconnected, and the board is shorted, it is time for a whole new board.
I've made +- DC power supplies on little pieces of insulation board. I screw them to the case with a standoff made of 1/4 air tubing and a #6 machine screw.
You take some board, like polycarbonate plastic window glazing or nema C laminate (canvas laminate board is what I use), drill some holes, run some wire with hooks bent in the end. Fly the 16 vac out the resistor holes, back in somewhere near the output connector. If you can't get the output connector not shorted, you pull the pins out, or splice into the three power wires with solder. You drill #19 holes for the mount screw and #27 holes for the wires. I could do this in about 2 hours.
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i'd say it's a bunch of mistakes in terminology.
if i understand you i think the center tap of that transformer winding is not making a connection (open circuit somehow)
if i understand you i think the center tap of that transformer winding is not making a connection (open circuit somehow)
Indianajo:
I interrupted the circuit at the resistors, how you said, measuring resistance at the end (+- out) i've got the DMM goin bananas.. Like: it starts from 150k and every second it changes the value, going downward mostly. Normal? Why that happens i dunno.
A new board?? 😱 If you do that in 2 hours, i do that in 2 months, man...
(Btw, what you mean for instance for #6, 0.6 mm? Or are you talking of inches?).
Turk:
At first sorry if my terminology isn't appropriate, if that is what you mean.. Not only am i a rookie in electronics, my english isn't perfect and i know that.
You all have been great in "interpreting" my english.
Anyway, what do you mean exactly with "the central tap is not making a connection? I mean.. I do have voltage across the resistors.. It stops at the bridge but there is continuity.. If the central tap of the transformer would be isolated, i wouldn't have any voltage drop at the resistors, would I ?
Thanks guys so much, can't stress enough on how much i appreciate your help..
I interrupted the circuit at the resistors, how you said, measuring resistance at the end (+- out) i've got the DMM goin bananas.. Like: it starts from 150k and every second it changes the value, going downward mostly. Normal? Why that happens i dunno.
A new board?? 😱 If you do that in 2 hours, i do that in 2 months, man...
(Btw, what you mean for instance for #6, 0.6 mm? Or are you talking of inches?).
Turk:
At first sorry if my terminology isn't appropriate, if that is what you mean.. Not only am i a rookie in electronics, my english isn't perfect and i know that.
You all have been great in "interpreting" my english.
Anyway, what do you mean exactly with "the central tap is not making a connection? I mean.. I do have voltage across the resistors.. It stops at the bridge but there is continuity.. If the central tap of the transformer would be isolated, i wouldn't have any voltage drop at the resistors, would I ?
Thanks guys so much, can't stress enough on how much i appreciate your help..
when you say "across the resistor"is that from one end of the resistor to the other or with respect to ground?
ok so as to not create anymore confusion describe to me where your DMM leads are connected for the measurements your taking and what your readings are?
what you where describing"the meter going bananas" was probably happening on a low resistance scale when you where checking for continuity(that would be cap's trying to charge and affecting your readings) but i might be wrong. i'm not there and i can't see what your doing so...
ok so as to not create anymore confusion describe to me where your DMM leads are connected for the measurements your taking and what your readings are?
what you where describing"the meter going bananas" was probably happening on a low resistance scale when you where checking for continuity(that would be cap's trying to charge and affecting your readings) but i might be wrong. i'm not there and i can't see what your doing so...
Across for me means one probe of an end and the pther probe to the other end. Like: in parallel with the component.
Going bananas means going crazy, the DMM display doesn't stop to any value, but i had the ohmeter selected, not the continuity mode. Still, the caps would affect the reading, wouldn't it?
Going bananas means going crazy, the DMM display doesn't stop to any value, but i had the ohmeter selected, not the continuity mode. Still, the caps would affect the reading, wouldn't it?
When you checked for a short on the board with the ohmmeter, you did still have the capacitors and regulators removed didn't you? The quiestion is, are the capacitors shorted? (2 v test with meter is inconclusive on 15 v cap) is the regulator shorted? (hard to test with meter) is the bridge shorted (you've checked) Is the board shorted? What else is there to short? Nothing IMHO.
Good capacitors should draw big numbers on the ohms scale, then decrease down to >100 kohms after the caps are charged up. I usually check them on 2000 ohms scale to charge them up fast, then click the meter up in scale to 200 kohm scale at the end.
Sorry about the US drill and screw numbers's, we use an old manufacturer's catalog numbers for small screws and drills. I think 3 mm screws are probably appropriate, but beyond that the drills and measurements are up to you. I don't have any metric hardware except a few screws for bicycles computers and things.
You would need a hand crank or electric drill, a vise, and a dirty shop area, anyway, to make a board. These tiny drills fit a hand crank Yankee drill chuck better than a 12 mm electric drill chuck. you cut a 4 cm x 10 xm piece of insulating board, draw out your parts with an indelible marker (sharpie here), spot some holes and start drilling.
Good capacitors should draw big numbers on the ohms scale, then decrease down to >100 kohms after the caps are charged up. I usually check them on 2000 ohms scale to charge them up fast, then click the meter up in scale to 200 kohm scale at the end.
Sorry about the US drill and screw numbers's, we use an old manufacturer's catalog numbers for small screws and drills. I think 3 mm screws are probably appropriate, but beyond that the drills and measurements are up to you. I don't have any metric hardware except a few screws for bicycles computers and things.
You would need a hand crank or electric drill, a vise, and a dirty shop area, anyway, to make a board. These tiny drills fit a hand crank Yankee drill chuck better than a 12 mm electric drill chuck. you cut a 4 cm x 10 xm piece of insulating board, draw out your parts with an indelible marker (sharpie here), spot some holes and start drilling.
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Man, i got all the replacement but the ceramics, and i changed everything.
Still 0v on out.
I think i have 2 options now:
1 find where the board is short and fix it somehow. Incredible i can't find the spot with the continuity mode of DMM.
2 pray all saints up there and rebuild a board with the components of this rail voltage. I don't like this option, i don't feel confident about it and i've never done it before so i actually don't know if im able to do it. I would if i would have a lot of time. It's kinda emergency option..
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