Studer A727/Revox B226 power supply mods.

RussianE39 · 15th March 2006, 02:09 PM

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?

Zoran · 16th March 2006, 09:27 AM

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?

Gasho · 16th March 2006, 02:29 PM

I think that Studer /Revox cdp´s use a low voltage switcher PS+LM for digital sections , and LM3xx for analog sections.

Zoran · 17th March 2006, 10:16 AM

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...

Bernhard · 26th July 2006, 01:41 PM

Hello,

I got a dead A727 that had a shorted 10000Âµ/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 ?

Bernhard · 26th July 2006, 03:42 PM

Netlist · 26th July 2006, 04:26 PM

The manual says -15 and +12V.
As for the IC, the picture in the manual shows an equal empty space.

/Hugo

Bernhard · 26th July 2006, 05:34 PM

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

Netlist · 26th July 2006, 05:39 PM

Quote:

Originally posted by Bernhard

Going out to buy fuses

And a pot...

/Hugo

Bernhard · 26th July 2006, 07:05 PM

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.

15th March 2006, 02:09 PM	#1
RussianE39 diyAudio Member Join Date: Jan 2006 Location: Moscow, Russia	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?

16th March 2006, 09:27 AM	#2
Zoran diyAudio Member Join Date: Jan 2004 Location: Belgrade	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? __________________ ###

17th March 2006, 10:16 AM	#4
Zoran diyAudio Member Join Date: Jan 2004 Location: Belgrade	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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16th March 2006, 02:29 PM	#3
Gasho diyAudio Member Join Date: Nov 2004 Location: Zagreb	I think that Studer /Revox cdp´s use a low voltage switcher PS+LM for digital sections , and LM3xx for analog sections.

26th July 2006, 01:41 PM	#5
Bernhard diyAudio Member Join Date: Apr 2002 Location: Munich	Hello, I got a dead A727 that had a shorted 10000Âµ/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 ?

26th July 2006, 03:42 PM	#6
Bernhard diyAudio Member Join Date: Apr 2002 Location: Munich

26th July 2006, 04:26 PM	#7
Netlist diyAudio Moderator Join Date: Jan 2003	The manual says -15 and +12V. As for the IC, the picture in the manual shows an equal empty space. /Hugo

26th July 2006, 05:34 PM	#8
Bernhard diyAudio Member Join Date: Apr 2002 Location: Munich	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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