Audio Precision P1 service manual?

Jump to Latest
#3
I did manage to get the service manual of System One if that of any use for someone here. But anyway it's not critical for what I'm trying to do.

I got me a Portable One Plus from 92 in working condition, though I did not test it thoroughly because of problem in the LCD inverter. The transformer is buzzing loudly à 1.2 KHz which is the switching speed of the inverter (I probed the transistors) with an output wave suggesting core saturation.

I'm suspecting an aging of the CCFL backlights which may be loading down the transformer. However when i put in a 3 Meg load on the secondary the transformer stops buzzing but the output wave is square with a lot of ringing and back emf.

I'm suspecting dysfunctional LC resonance, and indeed when I pulled out the 100µF cap in parallel with the primary winding, I found that it tested OK in DC, but the capacitance went down to 89 µF à 1KHz with an ESR of several ohms.

I'll receive a new nichicon cap tomorrow to replace it hoping that this will solve the inverter buzzing problem, else I will need to change the whole LCD unit (retrofitting a LED LCD).

This is a bit tricky because the LCD unit is controllerless, the kind almost impossible to get these days...
 
  • Like
Reactions: akem
#4
Ok so changing the capacitor got rid of the core saturation, but the transformer is still buzzing...

But wait! what the...😕 the transformer is 60 Hz! I didn't notice that before 😱:headbash:
 

Attachments

  • tran.jpg
    tran.jpg
    102.9 KB · Views: 277
  • Like
Reactions: akem
#7
I'm no engineer but the circuit looks pretty easy to reverse engineer since it's essentially analog with discreet circuits (the portable one plus unit).

I'm going to replace the transformer with a ferrite one that can handle more current. It should solve the problem since the LCD itself is working normally save for the aging backlight
 
  • Like
Reactions: akem
#8
Hello dear friends, I have an AUDIO PRECISION PORTABLE ONE PLUS and am looking for a display. Does anyone have any information where I can get one? My Display shows Hieroglyphen, the integrity is ok
I thank you for the information
 
#10
Hello,
Maybe the display shown at the bottom of this site, https://www.surplussales.com/Bulbs-Incan-Panel/LCDDisplay.html, is the one that some AP P1s use, there are different displays in these AP P1s.
But you have to check the AP P1 you have so that it is correct, otherwise if you are careful you can take apart the display and clean the Zebra contacts that are against the gold-plated contact sheets on the circuit board, the back light can perhaps be arranged with EL strips available at Conrad in Germany or any LED strips can shine down on the display window.
 
Last edited:
#12
Princetone said:
I did manage to get the service manual of System One if that of any use for someone here. But anyway it's not critical for what I'm trying to do.

I got me a Portable One Plus from 92 in working condition, though I did not test it thoroughly because of problem in the LCD inverter. The transformer is buzzing loudly à 1.2 KHz which is the switching speed of the inverter (I probed the transistors) with an output wave suggesting core saturation.

I'm suspecting an aging of the CCFL backlights which may be loading down the transformer. However when i put in a 3 Meg load on the secondary the transformer stops buzzing but the output wave is square with a lot of ringing and back emf.

I'm suspecting dysfunctional LC resonance, and indeed when I pulled out the 100µF cap in parallel with the primary winding, I found that it tested OK in DC, but the capacitance went down to 89 µF à 1KHz with an ESR of several ohms.

I'll receive a new nichicon cap tomorrow to replace it hoping that this will solve the inverter buzzing problem, else I will need to change the whole LCD unit (retrofitting a LED LCD).

This is a bit tricky because the LCD unit is controllerless, the kind almost impossible to get these days...
Click to expand...
Are you willing to share the service manual with me? I want to re-calibrate the Portable one i have. Also looking for the latest eprom, which version do you have?
 
You must log in or register to reply here.
Top Bottom