And now for the unexpected results...
These are in order C5 on top, C8 on the bottom.
I did these with a normal probe (not my differential) which is why the shots show 10x and not 50x.
I think I might have cooked something. Early on in my diagnosis, someone told me that I wouldn't get a smooth DC output at 12v when only feeding the board 12v and to roll up the AC voltage. I checked the specs of the LD1284V and it said max voltage is 30, I have a 24v toroidal transformer so I rolled the voltage on the board up to 24 volts to see if the signal would get better (only briefly).... but I wonder now if I cooked the caps?
Thanks
These are in order C5 on top, C8 on the bottom.
I did these with a normal probe (not my differential) which is why the shots show 10x and not 50x.
I think I might have cooked something. Early on in my diagnosis, someone told me that I wouldn't get a smooth DC output at 12v when only feeding the board 12v and to roll up the AC voltage. I checked the specs of the LD1284V and it said max voltage is 30, I have a 24v toroidal transformer so I rolled the voltage on the board up to 24 volts to see if the signal would get better (only briefly).... but I wonder now if I cooked the caps?
Thanks
Indeed unexpected. As far as I can see, the rectifier diodes D1-D4 do not function correctly such that the input voltage is not rectified.
Do you have a setting on your multi-meter that allows you to test the function of diodes?
If so, disconnect power to the transformer and check the function of all 4 rectifier diodes.
Do you have a setting on your multi-meter that allows you to test the function of diodes?
If so, disconnect power to the transformer and check the function of all 4 rectifier diodes.
And when you swap the multi-meter test pins (the other way), no conduction? 😕
The low values could hint use of Schottky diodes (lower forward drop).
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yes no conduction when connecting in reverse.
while I was probing around, I found that the traces from C10 were not making contact to C6. I have a spare board so I’m moving some things over to the spare board... stay tuned.
while I was probing around, I found that the traces from C10 were not making contact to C6. I have a spare board so I’m moving some things over to the spare board... stay tuned.
Staying tuned....
If there is a risk that the circuit you have (the connections between the components) are not such as shown in the small schematic, we will continue to make flawed conclusions. In case of doubt of the actual circuit, there is the tedious job of checking all connections with an Ohm-meter. It may take an hour for the whole circuit but it is possible. I work a lot on Vero-board where I create my own circuits and I do that as an important check before putting power on.
Still tuned.........
If there is a risk that the circuit you have (the connections between the components) are not such as shown in the small schematic, we will continue to make flawed conclusions. In case of doubt of the actual circuit, there is the tedious job of checking all connections with an Ohm-meter. It may take an hour for the whole circuit but it is possible. I work a lot on Vero-board where I create my own circuits and I do that as an important check before putting power on.
Still tuned.........
Ok, so I didn’t check EVERY trace on the spare board, but I moved the missing components over from this board and verified most of the traces with the mulitmeter (just following the printed lines on the board).
I hooked it up and redid the measurements of the 4 caps - same story. The diodes on this board measure slightly different, but similar to the previous board with one pair on the left side of the board measuring slightly different from the pair on the other side.
I hooked it up and redid the measurements of the 4 caps - same story. The diodes on this board measure slightly different, but similar to the previous board with one pair on the left side of the board measuring slightly different from the pair on the other side.
OK.
Next 8 tests (with reference to the small schematic you posted in your first posting):
Scope-probe ground-clip connected to point "C".
1) Scope-tip connected to cathode of D3 (directly on the diode lead). Expected voltage curve - 37Vpp sine-wave.
2) Scope-tip connected to anode of D4 (directly on the diode lead). Expected voltage curve - 37Vpp sine-wave.
3) Scope-tip connected to cathode of D4 (directly on the diode lead). Expected voltage curve - positive sine-wave halves (18V peak) but no negative.
4) Scope-tip connected to anode of D3 (directly on the diode lead). Expected voltage curve - negative sine-wave halves (18V peak) but no positive.
Scope-probe ground-clip connected to point "A".
5) Scope-tip connected to cathode of D1 (directly on the diode lead). Expected voltage curve - 37Vpp sine-wave.
6) Scope-tip connected to anode of D2 (directly on the diode lead). Expected voltage curve - 37Vpp sine-wave.
7) Scope-tip connected to cathode of D2 (directly on the diode lead). Expected voltage curve - positive sine-wave halves (18V peak) but no negative.
8) Scope-tip connected to anode of D1 (directly on the diode lead). Expected voltage curve - negative sine-wave halves (18V peak) but no positive.
Let's see the results of that.
Next 8 tests (with reference to the small schematic you posted in your first posting):
Scope-probe ground-clip connected to point "C".
1) Scope-tip connected to cathode of D3 (directly on the diode lead). Expected voltage curve - 37Vpp sine-wave.
2) Scope-tip connected to anode of D4 (directly on the diode lead). Expected voltage curve - 37Vpp sine-wave.
3) Scope-tip connected to cathode of D4 (directly on the diode lead). Expected voltage curve - positive sine-wave halves (18V peak) but no negative.
4) Scope-tip connected to anode of D3 (directly on the diode lead). Expected voltage curve - negative sine-wave halves (18V peak) but no positive.
Scope-probe ground-clip connected to point "A".
5) Scope-tip connected to cathode of D1 (directly on the diode lead). Expected voltage curve - 37Vpp sine-wave.
6) Scope-tip connected to anode of D2 (directly on the diode lead). Expected voltage curve - 37Vpp sine-wave.
7) Scope-tip connected to cathode of D2 (directly on the diode lead). Expected voltage curve - positive sine-wave halves (18V peak) but no negative.
8) Scope-tip connected to anode of D1 (directly on the diode lead). Expected voltage curve - negative sine-wave halves (18V peak) but no positive.
Let's see the results of that.
edit: Sorry -- FauxFrench probably already covered this. I'll study that.
OK. So do I understand correctly at this point, you have a partially populated 2nd board that is giving almost the same measurements?
Are the rectifiers fitted the same way? Does each transformer lead (only of the one secondary we're measuring) have a rectifier anode AND a cathode connected to it?
Then, are the other ends of those rectifiers connected anode to anode, and cathode to cathode?
OK. So do I understand correctly at this point, you have a partially populated 2nd board that is giving almost the same measurements?
Are the rectifiers fitted the same way? Does each transformer lead (only of the one secondary we're measuring) have a rectifier anode AND a cathode connected to it?
Then, are the other ends of those rectifiers connected anode to anode, and cathode to cathode?
The pcb has three connections for the four transformer wires. Can you show us how you have connected? I assume that you have all diodes in place.
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Posting #1, one of the links include a small schematic. I hope this is the circuit we work on. I still keep the possibility open that the real circuit may be different.
My browser (Chrome) won' t open the schematic on the OP. Does anyone have a jpeg or png of it they could upload?
peranders' point might be the clue I've been missing ..
peranders' point might be the clue I've been missing ..
And here are close-ups of the board as it sits presently. The diodes appear to measure similarly on each board.
And Rick, I think this is the preferred method of sharing a link on here... here's the link from the OP.
Many thanks for the photos.
Please switch of the 120Vac power to the transformer.
Please use the Ohm-meter and measure:
1) resistance between the anode of D1 and the "-" terminal of C5,
2) resistance between the anode of D3 and the "-" terminal of C5,
3) resistance between the cathode of D2 and the "+" terminal of C5,
4) resistance between the cathode of D4 and the "+" terminal of C5,
Please switch of the 120Vac power to the transformer.
Please use the Ohm-meter and measure:
1) resistance between the anode of D1 and the "-" terminal of C5,
2) resistance between the anode of D3 and the "-" terminal of C5,
3) resistance between the cathode of D2 and the "+" terminal of C5,
4) resistance between the cathode of D4 and the "+" terminal of C5,
Many thanks for the photo of the board. My immediate impression is that the copper tracks I can see are according to the schematic. But, I also notice that the solder has not penetrated the mounting holes and entered on the component side. Could it be that there are no conductive platings in the holes assuring a connection between the two sides of the PCB? In such case you need to perform all the solderings on the component side as well. That will be (very) difficult below the electrolytic capacitors. If this is the reason for the strange behavior, the effective circuit is not at all as we assume because a lot of connections are broken.