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#21 |
New Member
Join Date: Sep 2020
City & State: Lexington, KY
My Country: United States
Line Voltage: 120VAC 60Hz
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![]() I did measure voltage going getting to each of the mosfet pins and everything was zero.
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#22 |
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Join Date: Sep 2020
City & State: Lexington, KY
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![]() Attached is an thermal image without the mosfets installed. The second pic has the labels. Not sure if this tells us anything. Took the picture with the sub hooked up with the dimbulb test with a 100 watt bulb in it. The bulb dimly lights up for moment and turns off.
Last edited by khajr; 10-01-2020 at 07:47 PM.. |
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#23 |
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City & State: Lexington, KY
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![]() Ya. I have been concerned as well and have been checking trace connections above and below the board.
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#24 | |||
master hoarder
Join Date: May 2008
City & State: VA (NoVA)
My Country: U.S.A.
Line Voltage: 120 VAC, 60 Hz
I'm a: Hobbyist Tech
Posts: 10,172
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![]() Quote:
Also, I don't see a schematic of a switching PS anywhere after the 200V caps and instead the two 200V caps provide two rails: P170V and N170V. Does this mean this amplifier IS NOT ISOLATED FROM LINE VOLTAGES? ![]() That would be a very bad design. If it really is not isolated by design, I HIGHLY suggest you only use a GFCI plug when you test voltages inside the amplifier. I also find it equally appauling that the two 15V power supplies, P15V and N15V are derived directly from the P170V and N170V supplies simply through a resistive drop circuit with Zeners used for regulation. Not only is this inefficient, but it means even the low-voltage rails are not isolated from mains? ![]() ![]() *EDIT* Looks like there are two P15V and N15V power supplies??? ![]() But then there is another set of P15V and N15V power supplies on the "safety side", and these appear to be generated from P32V and N32V power supplies, which come from a transformer, meaning they are actually isolated from the line side. That makes more sense then. Otherwise, I don't see how it would be even possible to sell this amplifier and still meet safety inspections. But then this suggests there are two P15V and N15V power supplies? Quote:
![]() We can try to figure out what they should be as well... but I'm not sure what you mean by those "P1", "P2", and "P3" test points. It would be easier if you use the component pin designators - i.e. Gate, Drain, Source. Quote:
As for the thermal images... looks like your hottest component are R8 and R6, which shouldn't be surprising at all. These are the resisitive droppers that provide P15V and N15V power supplies. And like I noted above, this is a very inefficient way to do that, so that explains why they are running hot. That said, seems like they are running around ~130F (54C), which isn't really that hot. So everything looks OK there. However, looks like Q4 is running hot, while Q2, Q3, and Q5 aren't (?) In that case, I suggest you remove Q4 and test it out of circuit. Better yet, replace it if you have spares. Also check the values of all resistors that connect to Q4. I don't believe Q4 should be running hot at all with the main transistors (Q1 and Q7) removed. While at it, also check the voltages across C21 and C27, then report back what they are. And if you can, check voltages across C5 and C6 as well (but be careful around these, since they are on the primary side.) Last edited by momaka; 10-04-2020 at 06:37 PM.. |
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#25 | ||
New Member
Join Date: Sep 2020
City & State: Lexington, KY
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![]() Quote:
Quote:
I will also check C21 and C27 and C5 and C6. Thanks so much for your help. |
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#26 | ||
master hoarder
Join Date: May 2008
City & State: VA (NoVA)
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![]() Quote:
In that case, Q4 and/or the sub-circuit around Q4 are definitely suspect, because you have 6V on the Gate of Q7, which means it's going to conduct as soon as a MOSFET is installed. Quote:
Just to be clear, we are looking for the voltages across these caps (but if you want to take out and check the caps with a cap meter in addition to measuring the voltages, that would be fine too.) An unbalance in the P15V and N15V voltage rails could also be the reason why there is a voltage on the Gate of Q7. |
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#27 |
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Join Date: Nov 2020
City & State: Toronto
My Country: Canada
Line Voltage: 120VAC 60Hz
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![]() Good afternoon. I also have a Prosub 60 subwoofer, and it also recently died on me. WhenI discovered your Badcaps thread, I was relieved to find someone else with - I believe - similar issues. My R19 is fried. I just checked Q1 and Q7. They are defective, too. I can replace those 3 components, and am prepared to test and replace additonal ones. However, I see that your thread seemingly ended, mid-repair, a few weeks ago? Did you hit a roadblock? Or - hopefully - did you get your Prosub 60 working? If so, I'd be grateful for any tips/insights beyond those in your thread. Many thanks. finster56
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#28 | |
New Member
Join Date: Sep 2020
City & State: Lexington, KY
My Country: United States
Line Voltage: 120VAC 60Hz
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![]() Quote:
I did hit a roadblock. My driver is bad. The first thing I did was perform the resistance check per DT and checked that the driver movement was free without noise/scratching. After swapping out the components and confirming there wasn't a short anymore I could indeed turn on the sub w/o the fuse blowing or a resistor blowing. I decided to hook it up to the stereo and I wasn't getting a very clear response from the sub. It was low and noisy. I checked the driver again and it scratches now when I apply pressure. I assume the voice coil is bad. Though there may be other components that are still faulty. So, the project is on standby until I get some time to work on it. But replacing the driver may not be cost effective...I am not sure yet...as I am not sure which driver I can buy to replace it. I guess I can get a voice coil repair kit, though I think I would also need a refoam kit. Again...may not be worth it cost wise. I already spent $30 on parts and shipping charges which I was fine with but spending anymore just might not be worth it unfortunately. Last edited by khajr; 11-13-2020 at 06:20 PM.. |
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#29 |
New Member
Join Date: Nov 2020
City & State: Toronto
My Country: Canada
Line Voltage: 120VAC 60Hz
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![]() Hello! Thanks so much for getting back to me.
Too bad about that roadblock. Yes, DT's drivers are unusual. Mine tested out with a bizarrely high resistance, too. However, I learned from other web sources that this was a design choice (beyond my current technical understanding). If it assists, I recall seeing the identical driver, but used, for sale. It was either on Ebay or Amazon. I think I just searched using the identifiers on the voicecoil shield. May I trouble you for a list of the components you ended up replacing? I appreciate that my problems may be a different, but I suspect they at least overlap. That list should assist me in focussing my troubleshooting. It also will be a wee bit easier to follow than the past thread. Good luck in the meantime with your repair quest. And keep safe. Cheers, finster56 |
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