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Success Stories If you have successfully repaired or restored a piece of equipment, why not write up what you did and post details here. Particularly if it was interesting, unusual or challenging. PLEASE DO NOT POST REQUESTS FOR HELP HERE! |
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11th Oct 2014, 2:08 pm | #1 |
Octode
Join Date: Apr 2007
Location: Hampshire, UK.
Posts: 1,574
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B&O Beomaster 8000 brain transplant
As I detailed on this forum earlier in the year, my Beomaster 8000 met with an unfortunate accident when the power was disconnected whist the set was operating at full output. The effect of this was to disable the microcomputer section, which is based around two 6500 mask programmed microprocessors. Whist no components were measurably damaged, the software contained on the chips would no longer run, rendering the unit inert and useless.
The Beomaster 8000 appeared in 1980 and was B&O’s largest, post powerful and most ambitious receiver. It can be therefore considered to be “the best of the best”. Its loss irked me considerably – the performance of the complete system is magnificent. I could of course have bought another one, but they have got expensive in the 20 or so years since I acquired this one and in any case that only delays the problem until the next time that it occurs. The factory don’t hold stocks of the chips either, so what to do? Having considered the alternatives, the only viable option seemed to be to rebuild the hardware around available home-programmable devices and then to re-write the software from scratch. The latter task was complicated by the lack of a working set to study and take measurements from and the lack of information generally about how the original software worked. The only documents I could find were the original user instruction manual, the service manual and a circuit description book. My marginal programming skills didn’t help either, so I brushed up on those before starting work. The compiler I used as Crownhill PIC Basic, this generates hex code which was transferred to the devices using a Microchip ICD2 and its accompanying software (Microchip IDE). The bulk of the interface between the original two microprocessors and the rest of the circuit is parallel so the architecture of two 40 pin devices in a master / slave configuration was retained to make enough ports available. I selected the PIC16F877A as the device for both positions and a clock frequency of 20MHz; this is divided down to 5MHz internally. Similarly to the original arrangement, one device controls power switching, source selection, control interaction between the receiver and the cassette deck / turntable (‘Datalink’) and remote control. The other primarily controls the FM tuner; there were no ASIC devices to do this in the late 1970s when this model was designed so the regulation of the tuner is performed almost entirely by the software. The other function of the second processor is as a port expander for the volume control, which requires 12 parallel bits (6 bits per channel). The first task was to assign the ports, then to modify the original PCB to accept the new chips. This mainly involved removing surplus components, such as the many pull-up resistors (not needed as the PIC16 device has CMOS outputs), the NV RAM (not needed as the PIC16 has this facility on board), part of the FM PLL frequency divider (not needed due to the higher crystal frequency) and the PLL frequency signal gate (not needed as synchronisation can be performed inside the relevant PIC). Originally the two processors communicated through a bi-directional 4 bit bus and interrupt line but as the language I used does not support interrupts in a meaningful way I abandoned this idea and instead used a single one-directional serial data connection which sends blocks of data about tuning, volume and source selection at the beginning of each instruction cycle. Having removed the surplus components, I linked up the pins of the existing chip holders to the correct parts of the circuit, cutting the tracks with a razor blade where necessary. The only changes were made on the microprocessor PCB, the rest of the set was left completely standard. To describe the software programmes completely would be outside what is permitted on this forum, but here are some key features: 1) A 3mS programme cycle is used to tie in with the data rate of the remote control and the ‘Datalink’ system. The programme repeats at this interval and is constructed so that the cycle time remains constant regardless of which functions are in use. 2) The display and keyboard are multiplexed in three phases so the programme addresses the relevant functions in three successive cycles, after which the process repeats. The three serial data blocks which are transferred to the second processor are linked to this process. The arrival of the data blocks synchronises the two processors. This link is handled by the on-board hardware asynchronous serial interfaces. 3) Although the compiler used has serial data routines built-in these could not be used for the remote control or the ‘Datalink’ functions as these need to integrate with the main programme cycle. Therefore these routines were coded from scratch; the ‘Datalink’ one is bi-directional so that the sources can communicate with the receiver as well as accept commands from it. 4) The FM tuning function retains the original 12.5 KHz resolution (although only 100 KHz resolution is displayed) and works entirely with integer mathematics, no floating point functions are required. This makes the code compact and fast, this is important with the time constraints which the 3mS programme cycle imposes. Never the less, to obtain the required resolution a cumulative approach is required to obtain the complete frequency measurement. Frequency measurement is made using one of the PIC16F877A’s on board timers gated by a software command. 5) The original “auto” and “manual” tuning modes are retained. “Auto” is an analogue mode where once the station as been located the AFT circuit takes over and the receiver tracks the station frequency, the display showing the measured frequency of the station displayed and the digital control ceases. In the digital “manual” mode the AFT system is disabled and the receiver is locked to the selected frequency by the internal quartz crystal reference. The display shows the chosen frequency which does not change regardless of reception conditions. 6) The original NV RAM (used for FM pre-set programme storage and default volume setting) has been abandoned. This required the -55V supply from the power amplifier to be brought up onto the microprocessor PCB and this was though to be in part responsible for the original problems. Instead the internal EPROM area of the PIC16 device is used; this stores the programme frequencies in “self modifying code”. There is a limit of how many times this memory can be written to (c. 100,000 to 1,000,000 times) so it can only be used when necessary. To ensure maximum longevity all new memory settings are stored in internal RAM whist the set is in use and only written to the EPROM (if necessary) when stand by mode is selected. For first time use and to recover from possible memory corruption the software inserts substitute values if the EPROM values are outside the expected range. I have tried to re-create the original user experience where possible and for all practical purposes the new software functions in an identical manner to the original, it is hard to tell that the set has been modified at all. Even inside the modifications are not visible when the screening covers are in place (not shown in the pictures). All the original functions are retained and the original key sequences are used to operate them. In addition, I’ve left and I2C port accessible should this be required (e.g. I2C volume control should the original and now unobtainable Analog Devices electronic attenuators fail) and there is plenty of room for new Datalink functions, e.g. control of a B&O CD player via the TP2 input. I’m very pleased with the result and can now easily replicate the software if the chips fail again. The greatly reduced power consumption is also a benefit; the whole thing runs much cooler and this must be a benefit to overall reliability. This is by a considerable margin the most difficult repair I have ever attempted so it is nice to have completed it. I think that this sort of activity will become increasingly necessary as the complexity of the equipment which falls into the “vintage” category gets more and more complex. I’m planning a re-write for the software for the matching turntable next, not through necessity this time as mine still works but out of recognition that it will be much easier to do with a working example to study. |
11th Oct 2014, 2:51 pm | #2 |
Dekatron
Join Date: Aug 2013
Location: Wigan, Greater Manchester, UK.
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Re: B&O Beomaster 8000 brain transplant
Congratulations, but that does not seem enough for what you have achieved. Really outstanding job.
Frank |
11th Oct 2014, 2:59 pm | #3 |
Octode
Join Date: Jul 2006
Location: Willand, Devon, UK.
Posts: 1,023
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Re: B&O Beomaster 8000 brain transplant
Most impressive Well done on such a complicated repair, it's well beyond anything I would be able do!
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11th Oct 2014, 3:01 pm | #4 |
Moderator
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Location: Oxford, UK
Posts: 27,787
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Re: B&O Beomaster 8000 brain transplant
Magnificent work.
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11th Oct 2014, 4:33 pm | #5 |
Dekatron
Join Date: Dec 2004
Location: East Yorkshire, UK.
Posts: 3,958
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Re: B&O Beomaster 8000 brain transplant
There are some very clever people on the forum, wish I was one of them. A lot of thought and effort has gone into this repair /modification. Well done.
John. |
11th Oct 2014, 4:58 pm | #6 |
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Re: B&O Beomaster 8000 brain transplant
I have done similar things myself but never such a big reversed engineered job. Did you find yourself thinking 'why did they do that? I would have done this instead' (or worse, revisiting an old design and thinking 'why did I do that'). It does look very good, a rare case of style and function. At least several million out of ten.
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11th Oct 2014, 8:58 pm | #7 |
Heptode
Join Date: Feb 2014
Location: Nottingham, UK.
Posts: 645
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Re: B&O Beomaster 8000 brain transplant
Absolutely outstanding piece of work. Few people could or would be able to go to such lengths.
Regards, SJM. |
11th Oct 2014, 10:36 pm | #8 |
Nonode
Join Date: Oct 2008
Location: Warsaw, Poland and Cambridge, UK
Posts: 2,669
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Re: B&O Beomaster 8000 brain transplant
Excellent job - I take my hat off to you! It takes real determination, as well as skill, to see something like this through to a finished, usable item.
Chris
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12th Oct 2014, 10:39 am | #9 |
Dekatron
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Location: Leominster, Herefordshire, UK.
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Re: B&O Beomaster 8000 brain transplant
Well impressed with this
You haven't lived in Cuba, by any chance?
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12th Oct 2014, 10:44 am | #10 |
Rest in Peace
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Location: Harlaxton, Lincolnshire, UK.
Posts: 3,944
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Re: B&O Beomaster 8000 brain transplant
I was service manager for a B&O dealer in Rutland when the Beomaster 8000 came out and it certainly was a nice piece of kit.
This sounds like an extreme example of modesty. To carry out this task must have taken a **** of a lot of skill and was in my opinion a major intellectual achievement. Well done. |
12th Oct 2014, 3:32 pm | #11 |
Nonode
Join Date: Jan 2004
Location: 1966-1976 Coverack in Cornwall and Helston Cornwall. 1976-present Bristol/Bath area.
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Re: B&O Beomaster 8000 brain transplant
Very impressive , just awesome.
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12th Oct 2014, 6:50 pm | #12 |
Octode
Join Date: May 2010
Location: Worcestershire, UK.
Posts: 1,880
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Re: B&O Beomaster 8000 brain transplant
Gobsmackingly epic Tim! Having heard your system I understand your motivation to recover it to working condition. Seriously impressive.
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12th Oct 2014, 7:20 pm | #13 |
Hexode
Join Date: May 2006
Location: Cambridge, Cambs. UK.
Posts: 469
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Re: B&O Beomaster 8000 brain transplant
Well done! I always felt like going home again whenever a dead 8000 came in to the workshop at Cambridge for repair. So damn heavy too!
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13th Oct 2014, 7:28 am | #14 |
Octode
Join Date: Apr 2007
Location: Hampshire, UK.
Posts: 1,574
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Re: B&O Beomaster 8000 brain transplant
Thank you everyone for your kind observations. In response to some specific questions:
The only thing that made me wonder why they did it was the NV RAM, this is a wretched arrangement that involves lots of extra circuitry and a -55V supply rather close to some very sensitive items. Battery-backed RAM would have seemed a simpler choice, which is what they used in the later models Beomaster 5000 and Beocord 9000. The rest is is a good first attempt (This was B&O's first generation of microprocessor controlled products), a little over-engineered in places but logical and solid all the same. No, I've not lived in Cuba but trying to run old cars here makes me sometimes feel that I do! Here are some pictures of the microprocessor board after the modifications. This isn't quite the final version, the SOIC8 adaptor was for an I2C EPROM which I thought I was going to need for the memory before I got to grips with how to use the internal one. It was later removed. The circuit is actually very simple, I moved as much complexity to the software as was possible as it is easier to modify and make flexible. |
13th Oct 2014, 12:21 pm | #15 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
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Re: B&O Beomaster 8000 brain transplant
Aha! That label in pic 1 was obviously the requisite red rag
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13th Oct 2014, 5:53 pm | #16 |
Dekatron
Join Date: Jan 2005
Location: Oxford, UK.
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Re: B&O Beomaster 8000 brain transplant
Incredible, Tim.
You've done the kind of thing that people talk about doing but never actually manage. Well done from me too. N. |
14th Oct 2014, 12:03 pm | #17 |
Octode
Join Date: Jul 2011
Location: Stockport, Greater Manchester
Posts: 1,208
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Re: B&O Beomaster 8000 brain transplant
I have heard this very system myself and to say it works perfectly is an understatement of considerable magnitude. An act of genius.
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Robert |
5th Nov 2014, 12:42 am | #18 |
Dekatron
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Location: Bewdley, Worcestershire, UK.
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Re: B&O Beomaster 8000 brain transplant
I am seriously impressed, speaking as one who usually replaces the back panel the minute an IC is spotted. What you have done is equivalent to putting the vacuum back into a duff valve! Very well done indeed, and a nice write-up too.
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5th Nov 2014, 1:04 am | #19 |
Dekatron
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Re: B&O Beomaster 8000 brain transplant
What a feat. Excellent work!
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Regards, Ben. |
5th Nov 2014, 9:31 am | #20 | |
Octode
Join Date: Jan 2003
Location: Ware, Herts. UK.
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Re: B&O Beomaster 8000 brain transplant
Quote:
I suspect that your set used an EAROM such as the ER1400 http://www.datasheetarchive.com/dlma...DSA-178575.pdf for non-volatile memory. Suitably low power CMOS SRAM such as the Hitachi HM6116 that could retain data for an extended period when battery backed only appeared in 1980 or '81 i.e. a year or two after your set was designed. John |
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