With the O2 switched off, there is no point in measuring the voltage at any op amp pins.
Are you saying you have 18.06VAC on the anode of D3 and 0VDC on the cathode of D3?
And the same DC voltage on both sides of D1??
Are you saying you have 18.06VAC on the anode of D3 and 0VDC on the cathode of D3?
And the same DC voltage on both sides of D1??
Hmm, looks like the problem is the -12v rail, or the 7912 itself (U6). The voltages seem correct after the diodes D3 and D4, so i'd check the polarity of the four caps and the soldering for U6. Next i would probe the pins on the 7912 (U6), the top most pin (1) is the GND, from there to the middle pin (2) should be in the input ~-18v, and from the top/bottom pin (3) the output should be ~-12v. You voltage directly after it at D5 is wrong so the problem has to be around there, and its all well before the power switch and op amps.
Also worth going to the link here, and following the section down the bottom for "initial DIY testing", there are a few of those pages for measuring resistances, and power.
NwAvGuy: O2 Details
Also worth going to the link here, and following the section down the bottom for "initial DIY testing", there are a few of those pages for measuring resistances, and power.
NwAvGuy: O2 Details
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More diagnosis information: I followed the Initial DIY Testing section to the letter. A red flag rose when I noticed there was something wrong in the pre-U2, voltage testing portion of that section and stopped. Previously, all other tests passed. Resistance was correct and capacitor polarity visually is correct. In answering sofaspud, yes, the diode measurements are as written with regards to the D1 and D3 measurements.
In an hour or so, I will perform the further testing mcandmar recommended.
In an hour or so, I will perform the further testing mcandmar recommended.
Meaning you have 0VDC at the U5 input and 17.34V at the U5 output?
I find that difficult to believe. Sorry.
My feelings aren't hurt.
Sorry if I made it seem like I did not pay much heed to your advice, because I certainly want your help, too. You have been one of the most helpful so far and were the first to enter in on the scene. I just didn't see any specific test criteria and, being a newbie at this, I didn't run with what you said. Maybe there was a test probe error with U5. I will test again and let you know. Thank you again!
I was hung up longer than expected. I will be testing momentarily. I look forward to your responses whenever they come. Thank you so much sofaspud, mcandmar, and agdr!
Thanks, everything's alright. It's I that should apologize for being so testy.
At this point I really think you should give the power supply section of the board another thorough visual inspection. Truly confirm that all polarized components (diodes, capacitors, & regulators) are oriented correctly. These kinds of mistakes can happen to anyone.
It's near impossible to determine the knowledge and experience of a poster. I'm just a junior leaguer 'round here, if that, and don't mind questions that a newbie might consider too silly to ask, or ones that are over my head. This was what I wrote previously:
This mostly repeats the advice from mcandmar, with a little extra thrown in. I also agree that the problem is close at hand, and these voltage checks will help narrow it down further to the exact component.
Just one more thing... when I write something like "measure pin 1 of U5" it is meant literally. Sometimes a cold solder joint can cause a problem, and using another point, as in "Ah, that's the same place in the circuit. I'll measure it there" can keep the problem hidden. Hopefully in this case it's just a helpful reminder.
At this point I really think you should give the power supply section of the board another thorough visual inspection. Truly confirm that all polarized components (diodes, capacitors, & regulators) are oriented correctly. These kinds of mistakes can happen to anyone.
It's near impossible to determine the knowledge and experience of a poster. I'm just a junior leaguer 'round here, if that, and don't mind questions that a newbie might consider too silly to ask, or ones that are over my head. This was what I wrote previously:
We can skip the AC input part now; the transformer operation isn't questionable. And you have a good ground reference at BT1- for all the DC voltage readings. Measure the DC voltage at the positive lead of C2 and the negative lead of C3. Measure pin 1 of U5, then pin 3. Measure pin 2 of U6, then measure pin 3. Then each side of D1 & D5.
This mostly repeats the advice from mcandmar, with a little extra thrown in. I also agree that the problem is close at hand, and these voltage checks will help narrow it down further to the exact component.
Just one more thing... when I write something like "measure pin 1 of U5" it is meant literally. Sometimes a cold solder joint can cause a problem, and using another point, as in "Ah, that's the same place in the circuit. I'll measure it there" can keep the problem hidden. Hopefully in this case it's just a helpful reminder.
Thanks everyone. I am online as you can see and I am in front of my equipment right now. I just got out of a digital circuits lab and I am now in front of the O2 board with the multimeter test probes ready. I double checked all diodes, all capacitors and all regulators for position and polarity and they are all in the correct orientation. I will (actually, no real insane wait) post updates for voltage in a moment.
EDIT: Nevermind. 🙂 Sleepness, even at MST, is getting to me.
EDIT: Nevermind. 🙂 Sleepness, even at MST, is getting to me.
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Results using BT1- as ground:
C2+ 18.1 V
C3- -18.1 V
U5 (top/bottom pins):18.1 V, 17.4 V
U6 (top/middle/bottom pins): 0 V, -18 V, ~-1 V (quickly drops, nearing ground)
D1 (top/bottom pins): 17.4 V, 17.4 V
D5 (top/bottom pins): ~3.5 V, ~2.5v (both rapidly decreasing upon contact)
Thank you sofaspud! Hopefully, you can make heads or tails of this. I have spare U5 and U6, generic MC7912CT and MC7812CT, on hand, purchased from my university shop, should any of those two be the problem.
Note: Mistyped C2- for C3-. Just now, I double checked the reading for good measure.
C2+ 18.1 V
C3- -18.1 V
U5 (top/bottom pins):18.1 V, 17.4 V
U6 (top/middle/bottom pins): 0 V, -18 V, ~-1 V (quickly drops, nearing ground)
D1 (top/bottom pins): 17.4 V, 17.4 V
D5 (top/bottom pins): ~3.5 V, ~2.5v (both rapidly decreasing upon contact)
Thank you sofaspud! Hopefully, you can make heads or tails of this. I have spare U5 and U6, generic MC7912CT and MC7812CT, on hand, purchased from my university shop, should any of those two be the problem.
Note: Mistyped C2- for C3-. Just now, I double checked the reading for good measure.
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U6 was it! Having replaced it, I am getting ~23.5 V now, per the DIY testing. It wasn't the electrostatically sensitive Q1/Q2 chips! I hope my success can feel like your success! Thank you, sofaspud! You help was timely and invaluable! Now, onto the U2 testing!
/Mcandmar shrugs shoulders and runs away....
Sorry Sofaspud if i'm complicating matters, just trying to help.
From the above, that confirms healthy AC coming in, and properly rectified DC post diodes at the filter caps, and at the two regulator inputs +/- 18v. From there it makes no sense, i can only assume a bad solder connection, or a short between the regulators and power switch, or a faulty regulator. (assuming power is off and no batterys connected)
I don't see any option other than removing them one at a time to see if you get any reasonable output from the other. I would pull the 7912 first and see if the + rail starts to behave normally.
Sofaspud may have a better idea?
Sorry Sofaspud if i'm complicating matters, just trying to help.
From the above, that confirms healthy AC coming in, and properly rectified DC post diodes at the filter caps, and at the two regulator inputs +/- 18v. From there it makes no sense, i can only assume a bad solder connection, or a short between the regulators and power switch, or a faulty regulator. (assuming power is off and no batterys connected)
I don't see any option other than removing them one at a time to see if you get any reasonable output from the other. I would pull the 7912 first and see if the + rail starts to behave normally.
Sofaspud may have a better idea?
Wow. It looks like both regulators are malfunctioning.
You have +18.1V for the U5 input, and -18V for the U6 input (which is good), but the outputs of both are garbage. They should of course be + and - 12V respectively. Since there are spares on hand, I'd go ahead and replace them. I suggest just clipping the leads and removing the leads remaining in the board with your soldering iron and long nose pliers. Put in the new ones, then repeat the voltage checks.
There's also the question of D1 that I mentioned before. There should be a small 0.3V drop across that diode. Let's worry about that later, though, and get the regulators at 12V output first.
You have +18.1V for the U5 input, and -18V for the U6 input (which is good), but the outputs of both are garbage. They should of course be + and - 12V respectively. Since there are spares on hand, I'd go ahead and replace them. I suggest just clipping the leads and removing the leads remaining in the board with your soldering iron and long nose pliers. Put in the new ones, then repeat the voltage checks.
There's also the question of D1 that I mentioned before. There should be a small 0.3V drop across that diode. Let's worry about that later, though, and get the regulators at 12V output first.
Hehehe no. Had an idea once, but it died of loneliness. Wish I'd have said the one-at-a-time, 7912 stuff. My memory of RS's testing procedure isn't too good. I'm guessing 23.5V is the measurement across the U2 power pins.
Just replaced U5, too. Will perform other measurements and report back shortly. I will then be offline around 11:15/11:30 PM MST. Thank you, sofaspud! And you were a big help, too, mcandmar, because it was you who pointed out the potential U6 problem!
Passed with flying colors on the U2 test. Both pins 4 and 8 measured -11.6 V and 11.7 V respectively on both of the output buffer stage op-amp sockets. So happy! 🙂
As is often the case with these things, the more eyes the better or you can stare a problem in the face all day and not see a solution. Glad you got it sorted in the end!
Now i'm off to bed as its 6am here and i'm still up browsing this forum 🙄
Now i'm off to bed as its 6am here and i'm still up browsing this forum 🙄
Passed the sections "Check The Raw DC Voltages" and "Check The Output for DC." Will insert batteries and run the ESD test for "IMPORTANT! Low Voltage Shutdown." Will also post photos for you guys to feast your eyes on! Thank you, everyone! So grateful!
Haha... I remember those days when I used to work on the dishroom crew for football games as a caterer. I was practically nocturnal, and only got 3 hours of sleep on weekends.
Pictures of the optimal, outrageously good Objective 2 amp! 🙂
Note the messy desoldering job on the bottom. I will have to do some cleanup tomorrow when energy and time permit!
By the way, ESD testing also passed!
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Note the messy desoldering job on the bottom. I will have to do some cleanup tomorrow when energy and time permit!
By the way, ESD testing also passed!
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An externally hosted image should be here but it was not working when we last tested it.
This is my current (partial) setup, that I have you guys to thank for! From left to right, there is the Superlux HD681 (modded, with angled velours), the newly working Objective 2 amp, a Monoprice premium 1.5 foot 3.5mm male-to-male interconnect and the Sansa Zip Clip, blue, 4 GB with inserted 16 GB SDHC, Rockbox'ed. I mention "(partial)" because I have a Shure SRH940 already waiting for me on Christmas!
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