Studer A727/Revox B226 power supply mods. - diyAudio
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Old 15th March 2006, 02:09 PM   #1
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Default Studer A727/Revox B226 power supply mods.

Hi!
After extensive experience with repairing that CDs I could tell you some facts. I'm willing that someone could prove it or tell me different version. So, I've repaired for now 4 of this CD-P's and ALL of them got HUGE power supply ripple (about 0.2 volts on +5V dig supply, and even 0.4-0.5 volt on +/- 10V supply rail for focus/radial motor tracking OPamp. Is this normal? It just slightly drops after recapping with new Panasonic caps. Also, +/- 10V supply rails for L272 focus/radial opamp is often not +/- 10V, for example 3 of CDp's got +10,4 / -12,5 after warm up. Is THIS normal? As I could see from schematic, that bug is made from factory - voltage regulator for -10V made on discrete transistor, not on usual LM337.
So, after all of this, is this worth to make clean power supply for that CDPs?
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Old 16th March 2006, 09:27 AM   #2
Zoran is offline Zoran  Serbia
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These days I am changing the old caps in PS
of B226, somehow I catch looking at the SCH,
that power supply is very common...
When I change PS big caps the sound was better...
probbably they was old 15 years or more.
Interesting, but this CD sounds with poor PS, better then most
other...
Power transformer is very good for my oppinion
maybe this is the key...
Consumption of the all system is lets say low
comparing with philips cds, because of les heatihg,
with smaller heatsink...
Maybe the tracking preregulator design (look at the 317 data sheet)
will do a better job, and it can be fit in same space at heat sink?
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Old 16th March 2006, 02:29 PM   #3
Gasho is offline Gasho  Croatia
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I think that Studer /Revox cdps use a low voltage switcher PS+LM for digital sections , and LM3xx for analog sections.
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Old 17th March 2006, 10:16 AM   #4
Zoran is offline Zoran  Serbia
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I saw sch,
and only LM317 and LM337 present
for digital part as well as for analog...
with a standard, chip manufacturer
recommended connection...
Very simple.
I shall post the sch...
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Old 26th July 2006, 01:41 PM   #5
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Hello,

I got a dead A727 that had a shorted 10000µ/16V Frako cap.

After replacement it still does not read disc.

Questions :

I measure -15V but only +12,2V for op amp supply. Is that right ?

On the prozessor / servo board there is an empty socket like for 8-pin op amp from the two L272 and the two pots to the upper left.
Is that ok or something missing here ?
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Old 26th July 2006, 03:42 PM   #6
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Click the image to open in full size.
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Old 26th July 2006, 04:26 PM   #7
Netlist is offline Netlist  Belgium
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The manual says -15 and +12V.
As for the IC, the picture in the manual shows an equal empty space.

/Hugo
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Old 26th July 2006, 05:34 PM   #8
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Thanks, sometimes when I press play, the player goes off completely.
Recently it was on for longer time and it played but with strong artefacts.
When I touched the upper pot with screwdriver to adjust, it blew one of the 1,25A fuses on the transformer/CDM1.
Going out to buy fuses

I love Studer / Revox , always multiple errors
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Old 26th July 2006, 05:39 PM   #9
Netlist is offline Netlist  Belgium
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Quote:
Originally posted by Bernhard

Going out to buy fuses
And a pot...

/Hugo
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Old 26th July 2006, 07:05 PM   #10
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Quote:
Originally posted by Netlist

And a pot...

/Hugo

No, but it really blows the fuse when I turn on of those two pots.
That wasn't the case first.
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