PL 400 series 1 XPL910 questions

[quirkaudio]

the +/- 15v test points both measure correctly- and yes at 60v both channels measure 0v at pin 6

 

[quirkaudio]

The low voltage +15 and -15 both measure correctly

 

[laatsch55]

Still no outputs in right?

 

[quirkaudio]

no outputs or drivers fitted

 

[quirkaudio]

I have measure the voltages on Q7, Q8 and Q9 on the left (faulty) channel- Q7 b 10v, e 10v, q8 e 8.4v b9.3v. This suggests that Q8 is functioning (b-e=0.9v), however on the good right channel Q7b 0.2v and e 1.5v and Q8 b 0.6v and e -0.5v.

Q9 on the left b 6v and e 8.7v, where as on the right it is b -1.2v and e 0v

pin 2 on the opamp on the left is 0v.

All the resistors test OK and visually everything seems to be OK

could the bias transistor be bad and causing this?

thanks for you assistance

Peter

 

[Gepetto]

I have measure the voltages on Q7, Q8 and Q9 on the left (faulty) channel- Q7 b 10v, e 10v, q8 e 8.4v b9.3v. This suggests that Q8 is functioning (b-e=0.9v), however on the good right channel Q7b 0.2v and e 1.5v and Q8 b 0.6v and e -0.5v.

Q9 on the left b 6v and e 8.7v, where as on the right it is b -1.2v and e 0v

pin 2 on the opamp on the left is 0v.

All the resistors test OK and visually everything seems to be OK

could the bias transistor be bad and causing this?

thanks for you assistance

Peter

Could be Peter

With the power off and bulk caps discharged, temporarily tack a wire between the bias transistor emitter and collector on the control board and try again. You will not be able to adjust bias but it will confirm or deny any concerns about the bias transistor health.

 

[Gepetto]

I have measure the voltages on Q7, Q8 and Q9 on the left (faulty) channel- Q7 b 10v, e 10v, q8 e 8.4v b9.3v. This suggests that Q8 is functioning (b-e=0.9v), however on the good right channel Q7b 0.2v and e 1.5v and Q8 b 0.6v and e -0.5v.

Q9 on the left b 6v and e 8.7v, where as on the right it is b -1.2v and e 0v

pin 2 on the opamp on the left is 0v.

All the resistors test OK and visually everything seems to be OK

could the bias transistor be bad and causing this?

thanks for you assistance

Peter

Some great close up photos of your control board build would be of great help Peter...it is hard to guess our way to success. Front and backside. Focus should be on the left channel.

 

[quirkaudio]

ok will do

 

[quirkaudio]

rear one to follow

 

[Gepetto]

rear one to follow

For starters, D4 is supposed to be a 10 ohm resistor. D3 is supposed to be the Schottky diode. D4 location is definitely wrong, D3 has to be checked.

 

[quirkaudio]

thanks so much for your keen observation, I will get on it and report back

 

[Gepetto]

Q1L looks somewhat beat up in the photo, can't really tell if it is just the photo or real. There is what appears to be a solder splash on top of the plastic case on Q9L that if it is, may be something that comes loose later on and causes problems.

I thought you ordered the Phoenix kit but I notice you have your bias transistor wires coming in on the topside rather than the bottom side of the board and you did not use the 3 pin Phoenix for this purpose. ??? Did you extend the bias transistor leads? I don't think the originals are long enough to reach the board front side. The bias transistor leads should be kept as short as practical which is why they enter from the back side.

Screws for the transistors Q2, Q2, Q6L and Q9L are flipped over. Screw head should enter from the bottom side of the board and the internal tooth lockwasher and nut should be on topside. Heat sink compound does no harm but is not needed.

That is what I observe so far Peter. Really need to see a bottom side photo too.

 

[quirkaudio]

@Gepetto -thanks so much- pin 6 is 0v....

would you advise putting the speaker protection in next or populating the drivers and outputs?

 

[quirkaudio]

@Gepetto- I did get the phoenix kit, but not the 3 pin sockets, the bias wires do reach

here is the bottom photo

thanks for your insight

Best
Peter

 

[MarkWComer]

@Gepetto- I did get the phoenix kit, but not the 3 pin sockets, the bias wires do reach

here is the bottom photo

thanks for your insight

Best
Peter

Looks like some things were left unsoldered in the upper right corner.

 

[MarkWComer]

Looks like some things were left unsoldered in the upper right corner.

Nevermind- I didn’t notice that the backside photo had the connector side up.

 

[Gepetto]

Peter you should clean your board again, You have a lot of residue and some solder balls left behind. The cleaning should leave the board surface whistle clean.

Also touch up some of your joints if you want it to be reliable. The photo shows cold solder in some areas of the photo. Work to get your board to look like this.

 

[quirkaudio]

thanks agian, I will clean and touch up now that is working-

 

[quirkaudio]

so one step forward, two backward.

The original 410 pre drivers all measured OK, however, when installed, the 10ohm resistors want to provide magic smoke and the current draw hits 1.5Amp plus - so is the MJ15022G a decent replacement for the 401's?

There is also the speaker protection board installed- and relay not engaging (as expected)

Thanks again

 

[Gepetto]

so one step forward, two backward.

The original 410 pre drivers all measured OK, however, when installed, the 10ohm resistors want to provide magic smoke and the current draw hits 1.5Amp plus - so is the MJ15022G a decent replacement for the 401's?

There is also the speaker protection board installed- and relay not engaging (as expected)

Thanks again

If your 410s measured good, doubtful they are the issue. Sounds more like a bias transistor lead broke and you have runaway bias if it smoked the 10 ohm resistors.