Nuuk
The "easiest" you can do is to unsolder the LT1084 plus the associated resistors and feed the amp with 9-12V DC from an external PSU. If it still drops so low, you probably have connected any diode in the wrong way, or there is a solder bridge somewhere. (The TA2020 has the fame of a durable device).
Regards
George
The "easiest" you can do is to unsolder the LT1084 plus the associated resistors and feed the amp with 9-12V DC from an external PSU. If it still drops so low, you probably have connected any diode in the wrong way, or there is a solder bridge somewhere. (The TA2020 has the fame of a durable device).
Regards
George
Now you mention diodes, can we confirm which end is the anode on those SMD diodes?
Looking at them from the top, with the writing on them the right way up, I have taken the right end to be the anode.
D20 is listed for discharging capacitor.
Looking at them from the top, with the writing on them the right way up, I have taken the right end to be the anode.
D20 is listed for discharging capacitor.
Nuuk said:
That is correct. There should be a small stripe on the cathode end of the diode package.
Thanks Brian because that's the way I have put them in. I measured them on a multimeter first so was fairly sure. But there is no stripe on the ones that I have!
Nuuk, I'm also having the same problem as yours. My 1kohm resistor is also measuring 800-830 ohm only. 🙁
Well that may be a good thing or a bad thing depending on what it is meant to be! 😉 We need to know what it measures on a working AMP-6.
So are you measuring 0.37 (or similar) volts across C1819 as well?
Hey NUUK,
I see about 1K across C18/19 with the probes in the correct polarity for the cap. About 130 ohms in reverse.
Are you sure those diodes have no stripe? I have yet to see one without. The stripes can be hard to see, so a strong light and a magnifier sure help!
I see about 1K across C18/19 with the probes in the correct polarity for the cap. About 130 ohms in reverse.
Are you sure those diodes have no stripe? I have yet to see one without. The stripes can be hard to see, so a strong light and a magnifier sure help!
Can't say we have the say measurement on c1819. Just noticed something, please correct me guys if I'm wrong. From the jp1 input (connected to secondary of trafo), ac power goes to the bridge rectifier, the dc from there goes to the 16,000uf bulk cap, then to the input of the regulator, the output of which goes to c1819, which is bypassed by d20 (discharge cap)? Therefore, if you check the resistance of d20, it seems to be charging up a cap, which I presumed to be c1819, thus, measuring the resistance of said cap is pretty useless.
I have already attached the tripath chip without going thru the voltage tests, is it still possible to do the voltage checks safely without damaging the tripath chip? If I attach my ac power without shorting pin 7 and 8 of jp3, this in effect puts the chip in sleep mode and thus won't be damaged in the event of faults in the power supply section?
I have already attached the tripath chip without going thru the voltage tests, is it still possible to do the voltage checks safely without damaging the tripath chip? If I attach my ac power without shorting pin 7 and 8 of jp3, this in effect puts the chip in sleep mode and thus won't be damaged in the event of faults in the power supply section?
Need help, while resoldering the resistors for the voltage adjustment, I accidently put to much solder on the right leg of r100, now, its connected to c102. Anyone with a clean board check if the right leg of c102 is connected to r100 by default? I'm afraid I screwed up my board 🙁
Yes, I'm quite sure Michael. I have one of those headsets with lights and different magnifying lens so I can see very clearly. There are no stripes! I tried to get a decent picture but failed miserably!🙁
Thanks! That looks about correct then. Well, I can't see what is wrong here so I am going to post this little $&£$% off to the Decibel Dungeon unpaid technician and see what he makes of it! 😀
Yes, you are OK there Dohbert, they are meant to connect! 🙂
Nuuk, is it possible the board itself is shorted somewhere? I removed the voltage regulator and still the 1k resistors registered very low. From my understanding of regulated PSUs, r100 should be connected to the output and adj pins of lt1084, while the 1k series with 68ohm is attached to adj and ground. If r100 measures ok, and the voltage regulator is not at fault, there are only 2 things I see that can cause the resistance drop: 1) a capacitor from Adj to ground (don't know what this is on the board) or 2) a capacitor from output to adj, after the voltage setting resistors (c1819). Any ideas?
Dohbert, your description of the voltage regulator circuit is correct! And my suspicion too is that there is a short somewhere!
Even if R101 + R102 measure 800 ohms instead of 1K, I should be getting around 11 volts output, not 0.37v!
I'm afraid that I can't offer a solution because I can't find one. T is going to take a look at mine so perhaps he can find the answer!
Even if R101 + R102 measure 800 ohms instead of 1K, I should be getting around 11 volts output, not 0.37v!
I'm afraid that I can't offer a solution because I can't find one. T is going to take a look at mine so perhaps he can find the answer!
I'll probably do a voltage test on c1819 next. Because of over eagerness, I also soldered in the ta2020 before doing the PSU test. Is it ok to do the PSU test, after adding the 1mohm load? Will it affect the ta2020 amp? Thanks
I just removed c1819, thinking it was the cause of the resistance troubles, but still, resistance for the 1kohm measured around 800ohm. So far I've removed lt1084 and c1819, so they're not the cause. I've also resoldered all the diodes, especially d20, since its the discharge diode, same results. I noticed something peculiar though, when measuring r101, instead of getting an outright 800+ohm, I'm measuing 300+ohm and this gradually increases to 800ohm, using my digial voltmeter. This is weird, as if it's charging up a cap while I'm measuring it. 
If the rest of the amp is in place, then you don't really need another load (but it shouldn't do any harm if you do). 😉
Nuuk, just wondering, if our measurements of r100 and 102 are correct, and the only resistor that measures quite low is r101, which might be caused by a parallel resistance somewhere) why not remove the leg of r101 that's connected to r100 from the board and connect it directly to r100's leg? If there is a short in the board, then we have bypassed it? Can we assume that the low resistance measurement of r101 is caused somewhere in the PSU section and not in the amplifier section, so that if we can't find any solution, I might try doing a snubberized PSU, ala carlos felipe, separately, then attach the DC output directly to c1819.
My AMP-6 is packed now and ready to send off to my 'Chief technician'! 😉
Ironically. I was going to leave off the PSU section and use SMPS but as I am reviewing this item, I thought it more correct to at least try it with the PSU that it comes with first!
I'm not sure how your suggestion of moving R101 would help!
Ironically. I was going to leave off the PSU section and use SMPS but as I am reviewing this item, I thought it more correct to at least try it with the PSU that it comes with first!
I'm not sure how your suggestion of moving R101 would help!
From my understanding of the PSU schematics attached by jan to the amp3 assembly instruction, one end of r101 is attached to adj of lt1084 and the other leg attached to r102. If r102 measures ok, why not remove r101 from the board, which we assume is causing the funky resistance measurements we're getting, then solder one leg of r101 directly to adj and the other to r102, so in effect we bypass the cause of the anomaly, but still get proper voltage adjustments? Hope my hunch is correct. I'll be trying it next 😀
Finally got what's causing the funky r101 resistance, its c100. By default, r101 should measure 1k regardless of how the probes are used, however, at its present state, it either measures 400+ohm or 800+ ohm depending on how the probes were connected. The same goes with c100, same resistance measurement as r101 depending on the probe's orientation. C100 shouldnt measure anything, at least on a digital vom. 🙂 Now, if you remove c100, you should get 1kohm. Anyone has any idea how c100 is attached to the regulator? Its suppose to be a ripple reject damping for the volt regulator.
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