Circuit needed for Durst power supplies EST 301 and EST 450

Discussion in 'Darkroom Equipment' started by Jose Velez, May 2, 2012.

  1. Jose Velez

    Jose Velez Member

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    Hi everybody,
    I'm trying to repair two Durst power supplies from a friend, respectively an EST 301 and an EST 450.
    I checked already the regulator board of the ES301 and it's clear that the PCB contacts of the current sensing resistors R42 and R43 and severely burned. There is a group of resistors nearby which I would like to substitute also, but it's no longer possible to read the respective value, as they have darkened considerably, like the surrounding PCB.

    I didn't open the EST 450 yet, but I may likely find a similar situation, therefore I will be grateful if someone can provide me the respective schematics.

    Thank you in advance,
    Jose
     
  2. ic-racer

    ic-racer Member

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    Quote from the following thread:
    http://www.apug.org/forums/viewpost.php?p=1245859
     
  3. cferrari

    cferrari Member

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    Jose,

    I have just got hold of an EST450 which I wasn't sure was working properly, and so had it apart, and can provide photos of the circuit. My one appears to be one of the later ones - the board is clean, but has some odd features (shorted out tracks on the back) which i'm not sure are original.

    Let me know if you want pictures, I can provide these and traces from the supply in use.

    [​IMG]
     
  4. ic-racer

    ic-racer Member

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    A couple of the Durst printed circuit boards I worked on have similar features. I believe those were to update the circuit. In one case the changes matched a 'circuit update' note on one of the schematics.
     
  5. cferrari

    cferrari Member

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    Ah, ok, thanks for that. I'm still wary of this transformer, it's also got a pair of 1 ohm resistors in series with the transformer on the power side, and these are of different makes and are glued to one end of the transformer (I guess with it acting as a heat sink). It's all a bit heath robinson compared to the rest of the design. I guess this could also be a circuit update as i've heard that they had a fairly high failure rate with this power supply....

    I've measured the light output of my L1200 with this supply and compared it to the output from a standard TRA450 and they are within measurement tolerance so it does appear to work in it's current form. I guess I should run it for 1/2 an hour and keep an eye on the temp on these extra components to ensure they don't melt a hole in the case ;-)
     
  6. Jose Velez

    Jose Velez Member

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    Hi cferrari,
    Thanks you for the support, but apparently the ones I'm trying to fix are much older, below you can see pictures of both regulator cards:

    EST 450 board:
    EST_450.jpg

    EST 301 board:
    EST_301.jpg
     
  7. ic-racer

    ic-racer Member

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    Have you measured them? Looks like it just might be surface damage on those resistors from the 'flames' thrown by the power resistor when it went bad.

    Were you able to contact Georges Giralt for the schematic?
     
  8. Jose Velez

    Jose Velez Member

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    Hi,
    I did not touch the 301 yet, but I'm also hoping that it is more "smoke than fire", literally.
    On the 450 I replaced the electrolytic capacitors and a burned resistor, but I must investigate further because the regulating transistor is driving too much current and burned again the resistor.

    I already sent a PM to Mr. Giralt (only one day ago, no answer yet). Hopefully he will be able to help me, as following the circuit without the schematics is much harder.

    Thanks, best regards.
    Jose
     
  9. ath

    ath Member

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    When the epoxy in the board gets brown or even black it stops to isolate and starts to conduct.
    A board like the 301 is probably beyond repair.
    Both look to be from the early 70ies, probably a good idea to replace all electrolytic capacitors.