troubleshooting definitive technology prosub 60

[khajr]

I did measure voltage going getting to each of the mosfet pins and everything was zero.

[khajr]

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.

[khajr]

Originally Posted by R_J

You need to be very careful working with these double sided boards, If you remove a through hole component and destroy the feed through, you will no longer have the circuit connection between one side and the other.

Ya. I have been concerned as well and have been checking trace connections above and below the board.

[momaka]

Originally Posted by khajr

I am using a 100 watt bulb in the dim bulb tester. With Q1 and Q7 removed the lit dimly for a moment and went out. Across C2 I get 168v. Across C4 I get 168 v. Across C2 and C4 I get 360v. Across the + and - of the bridge rectifier I get 336v.

Looks like your power supply, at least on the primary side, is OK.

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? Am I the only one that's catching this BS, or is the schematic drawn incorrectly?

*EDIT*
Looks like there are two P15V and N15V power supplies??? Because one appears to be generated from P170V and N170V on the "line side", as mentioned in the schematics.
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?

Originally Posted by khajr

I tested to voltage at the connections for the mosfets and found the following:

Q1
P1 and P2 = +169V
P2 and P3 = -169V
P1 and P3 = -300mV

Q7
P1 and P2 = +163V
P2 and P3 = -169V
P1 and P3 = -6V

I will try and figure what they should be.

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.

Originally Posted by khajr

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.

It's normal for the bulb to light up for a moment and then go out when plugging in a device with large input primary caps (i.e. the two 200V caps.) Basically, since the 200V caps are uncharged, they pull a substantial "surge" current as they become charged when the amplifier is plugged in, which is what makes the bulb glow. Once fully charged and at their normal voltage operation levels, the surge current stops and the bulb goes out.

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.)

[khajr]

Originally Posted by momaka

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.

Hey momaka...Sorry I was referring to the pins for that mosfet. 1 is gate, 2 is drain, and 3 is source.

Originally Posted by momaka

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.)

It only appears that Q4 is warm. I will test as I don't have any spares. I tested R12 and it was fine. I will have to figure out where R5 is. Most of the resistors are soldered right next to the board and I can read the screen printing underneath them but I can figure it out.

I will also check C21 and C27 and C5 and C6. Thanks so much for your help.

[momaka]

Originally Posted by khajr

Hey momaka...Sorry I was referring to the pins for that mosfet. 1 is gate, 2 is drain, and 3 is source.

Ah OK.

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.

Originally Posted by khajr

I will also check C21 and C27 and C5 and C6. Thanks so much for your help.

No problems.

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.

[finster56]

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

[khajr]

Originally Posted by finster56

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

Hello Finster

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.

[finster56]

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