Phase Linear 2000 troubleshooting

[Coldsmoke]

The 4739's are a very weird duck. I have tried quite a few in it's place and they always oscillate. Joe tells me it has something to do with bandwidth and phase angles. We were going to rework the circuit on a 2000 to accept a different op-amp one of these days but so far have not done it...

Just you to know Lee , I just found a store here that sells NOS 4739, for... 20€ :/

 

[Coldsmoke]

BTW, I have a little doubt, I am about to replace the resistors on the 2000, I noticed that several changed a bit over time (more than 20% sometimes), I bought metal film resitors (5% 1/2W) but I suddendly have a doubt about the power rating of the current ones, they are so big! It is 1/2W right?

 

[laatsch55]

The schematic should tell you what is 1/2 watt and 1/4 watt. While you are upgrading you might consider 1% MF. Are those 4739's new??

 

[laatsch55]

Just you to know Lee , I just found a store here that sells NOS 4739, for... 20€ :/

That might be a good idea. Mine are all used so who knows how long they might last..

 

[Coldsmoke]

The schematic should tell you what is 1/2 watt and 1/4 watt. While you are upgrading you might consider 1% MF. Are those 4739's new??

I didn't found these precisions about power rating in the manual :/

Yes, the 4739 are new : https://www.selectronic.be/selectronic_catalogsearch/results/?q=rc4739

 

[Coldsmoke]

That might be a good idea. Mine are all used so who knows how long they might last..

If you don't mind Lee, I think I'll give a try to yours first, having spent a bit of money on the 400 lately

 

[laatsch55]

Will do Florian..

 

[Coldsmoke]

Will do Florian..

Thanks Lee... I don't know how to thank you for this...
About the power rating, I finally found a note that states 1/2W 5% CF, like for all resistors, I didn't found anything about 1/4W values

 

[laatsch55]

Anything not specifically noted separately on the schematic is 1/4 watt. The only 1/2 watt IIRC are in the power supply section.

 

[laatsch55]

Florian, I just pulled the covers on my 2000 and sure enough , they're all 1/2 watt resistors, my bad....

 

[Gepetto]

Florian, I just pulled the covers on my 2000 and sure enough , they're all 1/2 watt resistors, my bad....

Most do not need to be, that was just a Phase Linear trait. I am sure it helped keep costs down by reducing the BOM master for the corporation.

 

[Coldsmoke]

Florian, I just pulled the covers on my 2000 and sure enough , they're all 1/2 watt resistors, my bad....

Ah ah I read and re-read the manual and the diagram at least for an hour So, I suppose I can replace everything with 1/2W 5% or 1% would really be an improvement?

 

[Coldsmoke]

Hopefully my last question (...) :
- I would like to replace the red LED with a white one to match my new LED board on the 400 any idea of the current and voltage through this led? I'd like to change it with a 3,2V 20mA
- R71 and R72 where mounted in parallel with another resistor down to 8,7k instead of 22k, if I understand correctly the manual, this is to increase the output level, I suppose I can stick to the 22k value with my PL400....??

Thanks again in advance

 

[laatsch55]

That's a Joe question...

 

[Gepetto]

Hopefully my last question (...) :
- I would like to replace the red LED with a white one to match my new LED board on the 400 any idea of the current and voltage through this led? I'd like to change it with a 3,2V 20mA
- R71 and R72 where mounted in parallel with another resistor down to 8,7k instead of 22k, if I understand correctly the manual, this is to increase the output level, I suppose I can stick to the 22k value with my PL400....??

Thanks again in advance

18 mA through the white LED

 

[Coldsmoke]

18 mA through the white LED

Ty Joe, so my LED fits

 

[Gepetto]

Ty Joe, so my LED fits

I don't think you want the front facing LED to be that bright Florian. You should see how bright it is with the existing resistor stack. It may be good. LEDs today have much higher mcd output than when that preamp was created.

 

[Coldsmoke]

I don't think you want the front facing LED to be that bright Florian. You should see how bright it is with the existing resistor stack. It may be good. LEDs today have much higher mcd output than when that preamp was created.

You are of course right Gepetto, it is 1200mcd, I suppose that I can adjust the intensity with the right resistor by the anode side, right?

Do you have a clue for R71 and 72 values BTW?

 

[laatsch55]

Florian, I was gonna send your package today but it's a national holiday and the post office is closed.....so it will be tomorrow. I've sent 20-TIS-97's, 20 TIS-93's, 2-4739's, and 1-DC protect board. The extra 97's and 93's are just because....if you have a friend restoring a Moog Synthesizer...you'll be a hero....

 

[Gepetto]

Hopefully my last question (...) :
- I would like to replace the red LED with a white one to match my new LED board on the 400 any idea of the current and voltage through this led? I'd like to change it with a 3,2V 20mA
- R71 and R72 where mounted in parallel with another resistor down to 8,7k instead of 22k, if I understand correctly the manual, this is to increase the output level, I suppose I can stick to the 22k value with my PL400....??

Thanks again in advance

Hi Florian
According to the stock PL2000 schematic that I have, R71 and R72 are supposed to be 16K ohms. Looks like some previous owner or Phase Linear ran out of 16K ohm resistors and was improvising?