troubleshooting definitive technology prosub 60

[Messor Animae]

Re: troubleshooting definitive technology prosub 60

Also have a ProSub 60 that hums.

[finster56]

Re: troubleshooting definitive technology prosub 60

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

[khajr]

Re: troubleshooting definitive technology prosub 60

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]

Re: troubleshooting definitive technology prosub 60

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

[momaka]

Re: troubleshooting definitive technology prosub 60

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.

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.

[khajr]

Re: troubleshooting definitive technology prosub 60

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.

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]

Re: troubleshooting definitive technology prosub 60

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?

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.

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]

Re: troubleshooting definitive technology prosub 60

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.

[khajr]

Re: troubleshooting definitive technology prosub 60

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]

Re: troubleshooting definitive technology prosub 60

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

[khajr]

Re: troubleshooting definitive technology prosub 60

If the drive to the mosfets is bad, then the mosfets will be turned on, when they are turned on they will act as a short. If the circuit is working, the mosfets will be turned OFF and only turn on with the audio signal, basically Q1 and Q7 will alternate turning on and off according to the audio signal, and the voltage on the speaker will vary +/- producing the audio.
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.

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.

[R_J]

Re: troubleshooting definitive technology prosub 60

If the drive to the mosfets is bad, then the mosfets will be turned on, when they are turned on they will act as a short. If the circuit is working, the mosfets will be turned OFF and only turn on with the audio signal, basically Q1 and Q7 will alternate turning on and off according to the audio signal, and the voltage on the speaker will vary +/- producing the audio.
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.

[khajr]

Re: troubleshooting definitive technology prosub 60

The new mosfets Q1 and Q7 ought to be here tomorrow or Friday. What is concerning is that I already swapped those out along with C2, C4, R19, D1, and U3. And the it still blew the fuse and R19. Maybe I got a bad component. My soldering sucks (its really pretty good). I know now to test the new mosfets before I install them.

[khajr]

Re: troubleshooting definitive technology prosub 60

NO problems.
You can check those voltages without Q1 and Q7... and in fact that might be better so you can confirm if your power supply is OK with the output transistors removed. Then once you fit back Q1 and Q7, you can see how they affect the power supply if something is still not quite right.

Attached is a pic of the board where C1/C2 and C3/C4 are. It looks like you either have C1 and C3 or C2 and C4. Since this is the large case I have C2 and C4.

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.

[momaka]

Re: troubleshooting definitive technology prosub 60

NO problems.
You can check those voltages without Q1 and Q7... and in fact that might be better so you can confirm if your power supply is OK with the output transistors removed. Then once you fit back Q1 and Q7, you can see how they affect the power supply if something is still not quite right.

[khajr]

Re: troubleshooting definitive technology prosub 60

Measure across the four caps after bridge rectifier D1, if that is more convenient. C1 and C2 are in parallel, so you should see the same voltage across them, and hopefully it should be around 160-170V DC, depending on how much voltage your dim bulb is dropping on the AC. Likewise, C3 and C4 are in parallel and should also have the same voltage across them. Lastly, placing your red (positive) multimeter probe on the positive lead of cap C1/C2 amd the negative (black) multimeter probe on the negative lead of cap C3/C4 should give around 320-340V DC. Alternatively, you can measure the DC voltage across the bridge rectifier (+) and (-) pins. Whichever you chose, just be safe and pick the one where you're not likely to touch any of the metal parts in that area, as those DC voltages are quite high and can be dangerous.

Thanks for the help momaka. I am waiting on new Q1 and Q7 mosfets to come in. Then I will check those voltages. Yeah...I am trying to be very careful. I took Q1 out and pins 2 (drain) and 3 (source) were closed. 1 (gate) and 2 (drain) were open. and 1 (gate) and 3 (source) were open. I am going to take Q7 out and check too.

[momaka]

Re: troubleshooting definitive technology prosub 60

Where should I be measuring the bridge rectifier?

Measure across the four caps after bridge rectifier D1, if that is more convenient. C1 and C2 are in parallel, so you should see the same voltage across them, and hopefully it should be around 160-170V DC, depending on how much voltage your dim bulb is dropping on the AC. Likewise, C3 and C4 are in parallel and should also have the same voltage across them. Lastly, placing your red (positive) multimeter probe on the positive lead of cap C1/C2 amd the negative (black) multimeter probe on the negative lead of cap C3/C4 should give around 320-340V DC. Alternatively, you can measure the DC voltage across the bridge rectifier (+) and (-) pins. Whichever you chose, just be safe and pick the one where you're not likely to touch any of the metal parts in that area, as those DC voltages are quite high and can be dangerous.

[khajr]

Re: troubleshooting definitive technology prosub 60

Where should I be measuring the bridge rectifier?

[khajr]

Re: troubleshooting definitive technology prosub 60

R7 is a ntc thermistor, it gets hot and the resistance goes down, thats how it works. it will not be the problem. The cold temperature is 20Ω It is just for inrush protection. they can fail open but this one is working. The bridge rectifier is also likley ok, check if you have + & - 170 volts, this voltage is likely lower with the lamp in line. but both + & - voltages should be close to equal.
I see Q1 and Q4 (or should that be Q7) and R19 are quite hot, it could be that the mosfets are turned on hard.
What is the voltage on the speaker line? that needs to be near 0 volts

The + and - voltages on the bridge rectifier were off by an order of magnitude and the there was current through the speaker wire.

[khajr]

Re: troubleshooting definitive technology prosub 60

R7 is a ntc thermistor, it gets hot and the resistance goes down, thats how it works. it will not be the problem. The cold temperature is 20Ω It is just for inrush protection. they can fail open but this one is working. The bridge rectifier is also likley ok, check if you have + & - 170 volts, this voltage is likely lower with the lamp in line. but both + & - voltages should be close to equal.
I see Q1 and Q4 (or should that be Q7) and R19 are quite hot, it could be that the mosfets are turned on hard.
What is the voltage on the speaker line? that needs to be near 0 volts

Yes. It’s Q7. Don’t know why I had Q4 in my head. All three pins on Q1 are shorted together. I will check speaker line voltage and the bridge rectifier. But I am going to guess the speaker line voltage is not going to be zero as it makes a hum.

My original replacement were the two mosfets, R19, the bridge rectifier, C2 C4. and the op amp. Would we still be concerned about the zener diodes at all?