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Old 29th May 2021, 8:47 am   #1
djsbriscoe
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Default Revox B261 Tuner repair

So I've just bought a Revox B261 tuner. It's coming from Lubeck in Germany. It was sold as defective, so I hope to fix it myself. Stay tuned.

David.
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Old 29th May 2021, 12:48 pm   #2
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Default Re: Revox B261 Tuner repair

Any description of the fault?

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Old 29th May 2021, 4:53 pm   #3
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Default Re: Revox B261 Tuner repair

According to the seller

"Technical condition is unfortunately defective, it works but nothing more happens!"

I've asked for further details but had no reply so far. So very much a gamble. We will see in a week or two. If it is non-repairable I'll have to sell it for parts (for instance if the MCU is blown for instance). I'm hoping it's a power supply fault that hasn't damaged anything else.
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Old 29th May 2021, 8:32 pm   #4
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Default Re: Revox B261 Tuner repair

Understood.

I bought a B252 to go with mine and its TWO mask programmed CPUs are not booting up. It's sat in pieces under the bench for a couple of years. I might make a new CPU board(s) and display for it sometime. It was described as faulty, with a good description of the fault, so I knew what I was getting into.

My 261 is working fine and sounds great.

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Old 30th May 2021, 7:58 am   #5
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Default Re: Revox B261 Tuner repair

If it is an MCU problem I may be able to use an Arduino or a PIC to control the SAA1057 synthesizer. It seems this chip is popular with pirate radio FM transmitter hackers (mentioned on the Radionecks forum). The older CBUS interface may be a learning experience as I'm only familiar with modern I2C interface. Where can I read up on the SAA1057?
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Old 30th May 2021, 10:42 am   #6
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Default Re: Revox B261 Tuner repair

Here is a circuit that can control a SAA1057 synth.

https://www.pira.cz/enpll.htm

Might breadboard one up and give it a try.


PS Or maybe a TSA5511 could be used instead of the SAA1057?

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Old 1st Jun 2021, 2:35 am   #7
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Default Re: Revox B261 Tuner repair

David, I have looked and decompiled some of the various codes out there for the SAA1057 like the one you linked to - in short - don't waste your time - very badly written.


I did reply to your direct message, not sure if you got it.
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Old 1st Jun 2021, 9:35 am   #8
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Default Re: Revox B261 Tuner repair

Quote:
Originally Posted by Terry_VK5TM View Post
very badly written.
Not surprising. So much firmware at large in the world is pretty bad. Perhaps because it's too easy to edit at the development phase that not enough care is taken to get things right first time, and not all bugs are found by first shipment time. Worse still are underlying structural problems, things too fundamental for a quick edit to do much about.

Certainly if I do take the long way round with the B252, it will be a modern CPU, a TFT display and all-new software that goes in. It would be tempting to write my own processor and put it on a large Altera PLD.

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Old 1st Jun 2021, 11:19 am   #9
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Default Re: Revox B261 Tuner repair

I downloaded and had a look in the manual for the Revox.

The micro does a lot more than just control the PLL - if it is shot, replacing it with a PIC is going to be some mean feat of engineering.
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Old 2nd Jun 2021, 7:23 pm   #10
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Default Re: Revox B261 Tuner repair

Quote:
Originally Posted by Terry_VK5TM View Post
David, I have looked and decompiled some of the various codes out there for the SAA1057 like the one you linked to - in short - don't waste your time - very badly written.


I did reply to your direct message, not sure if you got it.
Thanks Terry,
I did get your message. I look forward to trying out the code for the FM transmitter that uses a rotary encoder an SAA1057 and an LCD. I'll have to brush up on my PIC assembler as I've mostly been using C (CCS PCM compiler) for the last few years.
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Old 5th Jun 2021, 6:51 pm   #11
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Default Re: Revox B261 Tuner repair

Well it arrived yesterday. While I was waiting for a 2 prong plug/cable to arrive, I opened up the case and removed/reseated all the connectors. Powered it on this morning and initially nothing happened. Then it suddenly sprang into life after a period of pressing the buttons repeatedly. So spurred on I did a proper contact cleaning session with servisol.
There is now a red LED lit above the store button when the mains power is turned on. It consistently turns OFF when I press the power button and I hear a relay click. However, turning it on can be a bit inconsistent as I have to press a preset button or a button at random to turn it on.
When the unit turns on I hear a relay click and a series of dashes on the LCD. Then the frequency appears on the LCD. The second LCD character has a few segments that don't light up. The output from the headphone output socket is distorted. The output from the variable output socket is not as loud, but it sounds a lot cleaner.
There is what seems to be signs of leakage from C20 and C21 (both 22uF FRAKO Electrolytic caps) on the Audio board (Ill post a photo later).
The buttons can store a station (I've put Radio 1 and 2 on buttons 1 and 2). The threshold knobs work. However, the unit randomly turns off sometimes when using the manual tuning buttons. The auto tune buttons work. The tuner has got stuck once and then I had to turn it off then on to get it working again.
I've not checked the power lines on my scope yet. Maybe it would benefit from recapping the power supply to clean up any noise present. The caps on the power supply look to have several pins instead of the normal 2 pins. What particular parts have others used for these? More later.
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Old 5th Jun 2021, 7:32 pm   #12
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Default Re: Revox B261 Tuner repair

I think some of the revisions f the boards were laid out for choices of size of some capacitors, but I don't remember multiple pins.

With a CPU, if it at least does something it is probably OK, and you've likely got connectors, dry joints and other components still to track down.

Distorted audio output could be more iffy connections, or dried out electrolytics. My B261 had baked itself for years in a rack of re-broadcast equipment, so the majority of electrolytics in the thing had gone high in ESR, so I just bit the bullet, put a big order into Farnell (Mixed Nippon Chemi-Con and Wurth parts) and set into one board at a time.

Beware that the copper tracks are thin, spidery and not too well adhered to the PCB substrate. expect lifted pads.

The PSU runs pretty warm, so you might not need the history of a hot rack to dry out capacitors. The original parts were not particularly high reliability types.

David
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Old 12th Jun 2021, 5:01 pm   #13
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Default Re: Revox B261 Tuner repair

Audio board recapped (Electrolytic only). Power supply board on the bench. Removed ALL small 10uF and one 4.7uF. All tested using a BK Precision 879B LCR meter and ALL have failed. Next, taking the big ones off.
Using Goot Wick CP-2015 2mm wide desoldering braid (fantastic stuff). More later.
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Old 13th Jun 2021, 6:46 pm   #14
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Default Re: Revox B261 Tuner repair

All large reservoir caps removed. All have tested OK, but I'm replacing them anyway with the following Vishay capacitors.

https://uk.farnell.com/vishay/mal213...-20/dp/2778023

and

https://uk.farnell.com/vishay/mal202...ole/dp/1165399
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Old 25th Jun 2021, 4:12 pm   #15
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Default Re: Revox B261 Tuner repair

Power supply, MCU board and audio board recapped. Still works and the receiver is getting more stable. It now turns on and off properly. Next is the stereo decoder board. Seven to replace on there.
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Old 21st Aug 2021, 6:09 pm   #16
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Default Re: Revox B261 Tuner repair

The Relay (American Zettler AZ7-4C-24D 4 pole double throw) on the audio board is faulty (contacts are measuring between 20 and 70 ohms). I am replacing it with 2 off Axicom IM07 miniature relays mounted on a custom PCB I've designed. Will post a photo when assembled and installed.
Once this is done, I can continue recapping.
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Old 3rd Oct 2021, 5:03 pm   #17
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Default Re: Revox B261 Tuner repair

I've replaced the original Relay mentioned above with a custom-made PCB. The PCB has 2 off Axicom IM07 24V DC sealed DPDT relays. The coils of the relays are in parallel. The picture shows the PCB installed on the audio board. Works great and the sound quality has improved as the audio signal is now going through nice clean contacts on new relays.

David.
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Old 18th Oct 2021, 8:47 am   #18
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Default Re: Revox B261 Tuner repair

Got a few segments working on the LCD again by moving the contact strip backwards and forwards on the glass. I've completed the recapping. Might at some point check the alignment. I will create a separate post for this, asking for assistance.
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Old 9th Aug 2022, 8:54 pm   #19
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Default Re: Revox B261 Tuner repair

Thread re-opened at OP's request

Cheers

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Old 9th Aug 2022, 9:32 pm   #20
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Default Re: Revox B261 Tuner repair

Thanks Mike,
I'm just wondering if anyone has ANY information on the old CBUS serial bus protocol used before the now ubiquitous I2C was invented? This is used in the B261 to control the LCD driver, PLL synthesizer and port expander as well as the EEPROM memory. There was a period of transition between the two protocols, and this resulted in some mixing of devices that used both. It would be great if there was more information on how this was implemented. Also, I'm not clear how the avoidance of conflicts was handled and how individual devices on the CBUS were addressed? Any information (including code examples in Basic, assembly or whatever) would be gratefully received. Thanks.
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