Rockford Fosgate Punch 200IX

[seankane]

What am I looking for after I lift Q226 and Q230?

 

[seankane]

Should I be lifting Q126 and Q130 to see if it gets rid of the DC on the 100 series channel?

 

[Perry Babin]

Those should disable the protection circuit. Does the amp draw excessive current?

 

[seankane]

Those should disable the protection circuit. Does the amp draw excessive current?

Lifted Q226 and Q230 and the amp actually draws less current now.

Shall I remove Q126 and Q130 as well or wait?

 

[Perry Babin]

Does that channel produce audio with those transistors out of the circuit?

If you have other transistors out of the circuit, reinstall them but leave 226 and 230 out for now.

 

[seankane]

Yes it does produce audio.

 

[Perry Babin]

Clean audio?

 

[seankane]

Yes it seems to be clean, but sounds kind of crackly when you get over 5/8 volume on the head unit. The bias is not set for this channel either.

 

[Perry Babin]

Is either of the transistors that are out of the circuit leaking or shorted?

 

[seankane]

Is either of the transistors that are out of the circuit leaking or shorted?

Well they both seem to be leaking. From collector to base I get 15.45 M ohms on both of them.

I checked a new one and it reads OL from collector to base.

This was out of the circuit testing of course.

 

[Perry Babin]

Clamp the transistors back down to the heatsink and drive a sine wave into a load. Does it produce a clean sine wave up to clipping and clip symmetrically top and bottom?

If so, reinstall Q226 and Q230, one at a time (preferably with new transistors if you have them). After installing one, do the same test as above. If it's still clean, install the other one and test again.

 

[seankane]

Clamp the transistors back down to the heatsink and drive a sine wave into a load. Does it produce a clean sine wave up to clipping and clip symmetrically top and bottom?

If so, reinstall Q226 and Q230, one at a time (preferably with new transistors if you have them). After installing one, do the same test as above. If it's still clean, install the other one and test again.

It was clean and symmetrical without Q226 and Q230 installed, and it was clean and symmetrical with one at a time installed and both installed.

Still dont understand how that channel can perform good on the scope seeing how Q245 Q244 and Q242 have no rail voltage and have +37 vdc on the drains, but there is no DC on the bridging terminal of that channel.

Thoughts???

 

[Perry Babin]

This amp doesn't use complementary output. I think it's called a quasi-complementary output stage. MTX has used a similar output stage extensively. Look at the schematic diagram to see how the outputs are connected.

Did you get the 100 series channel working?

 

[seankane]

This amp doesn't use complementary output. I think it's called a quasi-complementary output stage. MTX has used a similar output stage extensively. Look at the schematic diagram to see how the outputs are connected.

Did you get the 100 series channel working?

No the 100 series channel still does not work.

It no longer has DC on the bridging terminal at idle but the dc slowly increases with the volume.

It is still distorted badly, and when viewed on the scope the channel only deflects below the baseline and clips only below the baseline.

Another wierd thing is when the rca plugs are hooked up and the volume down the amp is quiet and idles fine. When you fire up the amp without the rca plugs hooked up the amp is very noisy inside hissing and squeeling, and makes tons of wierd noises through the speakers.

 

[Perry Babin]

Lift Q126 and 130. What changes with those out of the circuit?

We'll deal with the noise when this channel is repaired.

 

[seankane]

Lift Q126 and 130. What changes with those out of the circuit?

We'll deal with the noise when this channel is repaired.

Lifted Q126 and Q130 nothing changes, still have DC increase with volume increase, Still same reading on scope only deflecting and clipping below baseline, and still very distorted.

 

[Perry Babin]

Connect a load and post a photo of the distorted waveform.

 

[seankane]

This is what it looks like at clipping, nothing above the baseline and not symmetrical above and below.

 

[Perry Babin]

If you haven't checked Q118, Q119 and R140, do so now.

Confirm that you read ~33 ohms between the emitters of Q118 and Q119.

What is the DC voltage on the collector of Q118?

 

[seankane]

If you haven't checked Q118, Q119 and R140, do so now.

Confirm that you read ~33 ohms between the emitters of Q118 and Q119.

What is the DC voltage on the collector of Q118?

OK DC voltage on collector of Q118 is 74.6 vdc.

I read 33 ohms between collectors of Q118 and Q119 because earlier I replaced R140 and R170 because they were both way out of tolerance.

With Q126 and Q130 removed the DC is gone totally and does not increase with volume. It also produces clean audio.

If I reinstall Q126 and Q130 the audio becomes very distorted.