Bottlehead Forum
General Category => General Discussion => Topic started by: JAN6189W on July 20, 2015, 04:39:47 AM
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Hey folks,
I'm getting voltages of approx. 31 vac on terms 1,2,4 & 5 of my power transformer in my FPIII (not upgraded). I'm also getting approx 271 vac on the terms where I'm supposed to be getting 165 vac. The voltage regulator fires; but, the au7's do not. I suspect I got power surged. I've check the diodes and resistors all around the pre and all I've check measure in spec. (Sigh. I love this pre, even with the upgrade and have had it for years. I'm hoping it's just the PT and that a replacement is still available.)
What ye think??
Thanks in advance.
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Those numbers do seem odd. Are you measuring the AC across the power transformer terminals? For example one would measure from 1 to 2 to see the AC mains voltage, from 4 to 5 to see the 6.3V heater voltage and from 6 to 7 or from 9 to 10 to measure the high voltage secondary.
The next test would be to unplug the amp and measure the resistance across each of these pairs of terminals. I don't recall what the spec values are and I am not in the office yet to check them. If you can post what you measure one of us will verify what the readings should be for comparison.
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Those numbers do seem odd. Are you measuring the AC across the power transformer terminals? For example one would measure from 1 to 2 to see the AC mains voltage, from 4 to 5 to see the 6.3V heater voltage and from 6 to 7 or from 9 to 10 to measure the high voltage secondary.
The next test would be to unplug the amp and measure the resistance across each of these pairs of terminals. I don't recall what the spec values are and I am not in the office yet to check them. If you can post what you measure one of us will verify what the readings should be for comparison.
I will recheck as noted and report back, soon. Thanks.
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Hmmm...
PT measurements:
1 -> 2 = 122.4 (wall current is a tad high)
4 -> 5 = 6.3
4 = 3.4
5 = 3.2
6 -> 7 = 174.9
9 -> 10 = 174.8
That makes it seem like it's not the PT ? Maybe the PSU? I'll have to measure the heaters...
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You have a working power transformer.
What lead you to believe that the power transformer was the problem? (In other words, what is the actual problem you're observing)
-PB
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You have a working power transformer.
What lead you to believe that the power transformer was the problem? (In other words, what is the actual problem you're observing)
-PB
Yes, I know that now. My MM was set wrong. My apologies. Correct values listed above.
The problem that remains is that, concerning the au7's... there's no "fire in the hole". :)
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You should measure the voltage from pin 4/5 to pin 9 on both of the 12AU7s. Post your values.
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You should measure the voltage from pin 4/5 to pin 9 on both of the 12AU7s. Post your values.
4/5 to pin (both au7s) = 0.0
H1 = 28.56
H2 = 28.56
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.077 on each diode (in the direction of flow)
.8 on the .62 5W resistor
continuity on ground wire between H1 and H4
Could it be the 10v 10000uf cap? I don't think my MM will due capacitance. H2 is suppose to measure higher than H1 according to the spec check sheet.
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Tube pins 4 and 5 should be soldered together. So measure from just one of them to tube pin 9.
I'm trying to verify that the transformer voltage is getting to the tube. You know now that you have transformer voltage.
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Tube pins 4 and 5 should be soldered together. So measure from just one of them to tube pin 9.
I'm trying to verify that the transformer voltage is getting to the tube. You know now that you have transformer voltage.
It does not appear voltage is getting to the tube. The MM doesn't move. It stays at 0.
LED doesn't light, either.
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Then that might be why the tubes are not glowing. Oh, I forgot to say that it would be DC voltage at the tube. So check from pin 4 to 9 for DC volts. If nothing there try from H1 To H2, again, DC volts. The LED will not light if the tubes are not glowing. We can come back to that after the tubes glow.
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Then that might be why the tubes are not glowing. Oh, I forgot to say that it would be DC voltage at the tube. So check from pin 4 to 9 for DC volts. If nothing there try from H1 To H2, again, DC volts. The LED will not light if the tubes are not glowing. We can come back to that after the tubes glow.
Sorry, pulled away on family matters.
H1 to H2 = 0.0 mV (vdc)
Gotta be that cap, right?
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It could be a solder joint that broke loose. You have the voltage at the transformer, it disappears between there and the tube sockets. Check every solder joint on the terminal strip where you rectify the AC into DC (sorry, I'm not looking at the manual, I can't give numbers). Give the components a little pressure to see if they wiggle. There would be your loose solder joint.
I seriously doubt that a component went bad, it could happen, but they are too new.
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It could be a solder joint that broke loose. You have the voltage at the transformer, it disappears between there and the tube sockets. Check every solder joint on the terminal strip where you rectify the AC into DC (sorry, I'm not looking at the manual, I can't give numbers). Give the components a little pressure to see if they wiggle. There would be your loose solder joint.
I seriously doubt that a component went bad, it could happen, but they are too new.
Immediate continuity between H2 and tube pins on either tube socket.
Immediate continuity between 5W resistor lead and 10K uf positive lead
5W .62 resistor shows an instantaneous "short" (both tests leads up close to either side of resistor body)
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You should be able to get continuity from H4 to tube pins 9. That is the negative side of the DC power supply. That verifies connection.
You have already gotten continuity from H2 to pins 4/5 of the sockets. That proves connection for the positive side.
If there is no DC between H2 and H4 the problem is in the diodes. It could still be 2 solder joints that worked loose. My FP 2 power wire fell off the power switch after 8 years. Touch them up and see what you find.
If you have a diode checker on your meter you can check them. Diodes read a high resistance in one direction and a low resistance in the other. My meter shows the reverse resistance and the forward voltage drop. So read the manual for your meter.
You asked if the cap might be bad, that is possible. The end that sticks up is supposed to be flat. Bad caps often bulge that end, or the other one you can't see. But if the cap were bad you would have lumpy DC not filtered DC at the tubes. If it shorted internally the fuse should blow.
The 0.62 Ohm resistor is pretty close to a short. The only way to verify it is to set your meter to the lowest resistance range, touch your meter leads together and note the reading. Then measure that resistor, the reading should be a little bit higher.
The LEDs will not light unless the tubes are heated and conducting. So getting the voltage to the heaters should solve that.
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You should be able to get continuity from H4 to tube pins 9. That is the negative side of the DC power supply. That verifies connection.
You have already gotten continuity from H2 to pins 4/5 of the sockets. That proves connection for the positive side.
If there is no DC between H2 and H4 the problem is in the diodes. It could still be 2 solder joints that worked loose. My FP 2 power wire fell off the power switch after 8 years. Touch them up and see what you find.
If you have a diode checker on your meter you can check them. Diodes read a high resistance in one direction and a low resistance in the other. My meter shows the reverse resistance and the forward voltage drop. So read the manual for your meter.
You asked if the cap might be bad, that is possible. The end that sticks up is supposed to be flat. Bad caps often bulge that end, or the other one you can't see. But if the cap were bad you would have lumpy DC not filtered DC at the tubes. If it shorted internally the fuse should blow.
The 0.62 Ohm resistor is pretty close to a short. The only way to verify it is to set your meter to the lowest resistance range, touch your meter leads together and note the reading. Then measure that resistor, the reading should be a little bit higher.
The LEDs will not light unless the tubes are heated and conducting. So getting the voltage to the heaters should solve that.
Grainger, I can't tell you how much I appreciate your responses.
Tonight, I was checking DC between H2 and H4 and came up with nothing, 0.0 vdc. Then, suddenly, I looked down and the LEDs were on!! Poof, just like that. I checked again and the MM said 6.5 to 6.6 vdc. I started poking and pushing the cap, the 5W resistor and the wires in the PSU to see if I could turn the LEDs back off; recreate the issue. No such luck (not complaining). On my next day off, I will re-touch all those connections for good measure.
Happy man, now. Here's to the next 7 years (and more). :D