ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
Tone board complete and a system test carried out, thus far everything works fine....I haven't replaced the ribbons yet for fear of tearing them as work continues, however the motor and clutch drives all work nice and smoothly now. Next up will be the input board, need to figure out how best to remove it first.
Need to have a think about this
It's not an easy one to work on. That's for sure.But you're doing fine.I would really recommend replacing tantals with tantals, though. A bit more expensive perhaps, but much better for preamplifer/tonecontrol circuits thanconventional alu electrolytics.
Martin
Ahh.....I didn't know this, I actually thought electrolytics where a better replacement....we live and learn. During gentle pulling and easing I discovered that the power amp was going to lend itself to restoration easier than the preamp board, which still looks awkward to remove.
And the other side.....looks like Mr Jarman kindly replaced the skeleton trimmers with pifer type encapsulated units, this leave me with a dilemma as I have acquired 25 turn bourne pots already, but I'm reluctant to change the existing ones just for the sake of it.
its a thoroughly nerve wracking exercise lifting this board out, all the various wiring looms resisting my efforts to tease it higher without snapping anything......
Again the other side......just need to blow all the dust away with an air duster and that's the power amp done..........not a delight to be sure.
Output amp back in and now had to haul out the preamp, loosened the four screws holding the jack plug plate in place (should have been five but one has been lost in the mists of time), this allowed me to pull the output capacitors forward and get access to the retaining clips on the pre amp board....more nerve jangling pulling and tugging
finally got it safely out far enough (I think) to be able to replace the thirty or so tantalum capacitors
In accordance with Martins advice I will order up a bunch of Tantalum capacitors as diredc replacements for those I intend to remove, will take some time out to calm my nerves before starting
Dillen: It's not an easy one to work on. That's for sure.But you're doing fine.I would really recommend replacing tantals with tantals, though. A bit more expensive perhaps, but much better for preamplifer/tonecontrol circuits thanconventional alu electrolytics. Martin
Hi Martin,
I have a couple questions regarding the tantalum capacitors here. Can you elaborate why they are better for the application in this case (versus a modern electrolytic capacitor)? My other question is if the tantalum capacitors are still good, why replace them with new tantalums? Shouldn't the original tantulum capacitors still be good? Or do they also tend to fail at this point in their service life?
Thanks,John
sonavor: Dillen: It's not an easy one to work on. That's for sure.But you're doing fine.I would really recommend replacing tantals with tantals, though. A bit more expensive perhaps, but much better for preamplifer/tonecontrol circuits thanconventional alu electrolytics. Martin Hi Martin, I have a couple questions regarding the tantalum capacitors here. Can you elaborate why they are better for the application in this case (versus a modern electrolytic capacitor)? My other question is if the tantalum capacitors are still good, why replace them with new tantalums? Shouldn't the original tantulum capacitors still be good? Or do they also tend to fail at this point in their service life? Thanks,John
Tantalum capacitors (tantals) were - and stil are - relatively expensive components, but they werechosen for a reason, - not because a capacitor was needed and some tantals just happened to be in the drawer.Tantals have certain pros over aluminium capacitors, that really shouldn't be ignored;Tantals have much less leakage.Tantals have a much better temperature stability (10-20 times that of an aluminium electrolytic cap).Tantals have a much lower ESR (10 times or more). The lower ESR also means that they havea better volumetric efficiency, i.e you can, popularly speaking, "fit a 1uF tantal where you would otherwisehave put a 10uF aluminium cap". (Of course it's not like that in all cases in reality and calculations will decidethe capacity needed, - but it helps to give an idea of the quality levels of the components).Tantals are much less noisy. They don't give the same "burst" of noise when charging and discharging begins, that aluminium caps do.In short, tantals are more "perfect" capacitors than aluminium caps. This makes them the superb choice for some circuits. - And less attractive for other.Generally speaking, tantals are the best choice for audio and video circuits, filtering, preamplifiers,tonecontrols etc. = the finer workings.Similarly aluminium caps should be chosen for power supplies and the likes = the rough and tough workings.It should be said though, that due to their very low ESR, tantals shouldn't be used in circuits witha healthy amount of feedback (unless taken into consideration of course).Keep them away from audio output stages etc. Use standard aluminium caps here (non-low-ESR is fine).If you fit f.e. a 10uF 63V aluminium capacitor in a circuit where it will only ever see a few volts - likecoupling capacitors in a typical preamplifier circuit, it will not be excited and it will diefaster than if it was used up closer to its rating, even if only occasionally.You could say that aluminium caps can "die from boredom".Tantals generally don't show the same tendency, they will last longer even if not excited andthey typically have a lower voltage rating too, so it's not at all as much of a problem.Early Beocord 6-8000s (a.o.) is a great example, where aluminium capacitors with a too high voltage rating wereused in the signal paths in some production units. Lower voltage rating aluminium capacitors were then fittedinstead but tantals would've been the better choice here, really.But nothing will last forever and tantals are no exception, they will eventually go bad and Iwouldn't expect any and all of the ones fitted up through the 1960s and 1970s to still beworking today, though surprisingly many will be found showing no signs of aging.In 1960s and 1970s B&O units, a typical pattern seems to be that the tantals are either still all good or all marginal.In other words, if one tantal is found bad - you might as well replace the lot.When repairing and restoring, it's a good general handrule to use tantals where the designers used tantals.They were chosen and paid for for a reason.
That is a very helpful explanation Martin. I appreciate it. It is great to have more background on why certain components were used. I did do a little reading into some of the modern tantalum manufacturer product information. It sounds like newer made tantalums should last even longer than ones thirty years ago.
Thank you for the explanation above, very informative. I find capacitors a very complex component for something that at first appears very simple, I can also confirm that the tantals are more expensive than the electrolytic units having just ordered over 40 of the little devils from RS. And I expect I will be revisiting the tone board shortly too....while its all disassembled. I am looking for a replacement speaker jack for this 6000 though, one is a bit wobbly and I suspect one of the retaining wings is missing....haven't had a close look yet but it seems favorite.....do you have one by any chance?
Its taken me over two hours this evening to replace eight capacitors on the pre amp board, I think they where the most difficult ones to reach so I'm hoping for an easier ride tomorrow
Getting there slowly but surely, managed to replace more this evening as access improves as I move across the board.
Finished replacing all the capacitors on the pre amp this afternoon and having replaced the board back into its slots and snapping the stand-off connectors back into place decided to test the work so far.
Connecting up a speaker to one of the outputs I plugged an Ipad into the AUX port and played bruce Hornsby.....the sound was there but sounded awful!...low and raspy and very distorted as the volume was lifted.
Powered down and got the magnifier lens out and started to look around....and found a red wire pulled off the corner of the Level Amplifier PC7, looking in the circuit diagram it either provides 60v to PC7 or it is the feed to the Tone Amplifier...difficult to say as there are three red wires that disappear into the wiring looms.......
Connected the wire back to the board and powered up to be rewarded with a nice mellow sound much more in keeping with what was expected, so....I'm happy that the work done so far has been good.
Those stiff wires are a headache.No plugs anywhere - doesn't help.Good job so far!
Thanks Martin.......next up is the Level Amplifier, had to lift the output amp back out in order to lift this board out, I've already removed the Dial and Dial cord to prevent any damage so will have the cord to re thread at the end of the day, I have purchased some new cord to replace the existing as it looks a bit worn. The level amp has the SQ Decoder plugged into the underside......after the ordeal of replacing all the caps I will have the challenge of re plugging the decoder back into the level amp board....
This Level Amp has proven to be very difficult to access, I have broken off three of the irritating single strand wires thus far....and I'm not quite done with this board yet.
The SQ decoder came out easily enough and re capping was very easy
I've decided to plug the SQ Decoder back into the Level Amp before I put it back in place.....not sure if this will be the easiest way to tackle the reassembly, but that will have to wait a couple of days.....the main reason being I have run out of capacitors and furthermore I'm burned out and need to open a bottle of wine ;¬)
I think I have given you a bit of a poison chalice here. A bit of a beast to work on as far too much in a small box! A separate power amplifier would have made sense! Obviously complicated by the very complex display. The slightly sad thing is that it simply isn't the best sounding receiver B&O made - one could argue that it is not even the best sounding quad receiver. It was however the first remote control and it is probably the most beautiful. You do know you need the Beocord 5000 which is even worse to work on! If you can get both those working, I am sure will earn the Martin seal of approval!
Peter
Peter......you know full well I'm enjoying every minute of this, it's the anticipation of what new or unforeseen dilema the machine will throw at me next. If I can successfully see this through to completion I would like to tackle the Beocord....just for the hell of it ;¬)
Back to the Tone Board to address the issue of the Tantal's
All was going well until the last but one cap....spotted this crack in the PCB, must have done it when I removed the board......the clip cant have been fully disengaged. The crack can be seen in this pic, I will need to solder a link around it before I put the board back in place
received the balance of components I required and completed the Level amp......bit of gentle easing and persuading got the board along with the SQ de-coder back into place with only 2 more single core wires breaking off.....fortunately I have plenty of pictures to help with the confidence of replacing them in the right place
also finished off the tone board this evening, all the aluminium caps replaced with tantals in accordance with Martins advice, I have also installed a link around the damaged track on the PCB....I know its a bit industrial in its size, but it is solid.
This done and the board replaced, I also put some epoxy on the dislodged piece of PCB, I had a quick look around under the magnifying glass and spotted another wire had decided it was in its own best interest to let go of its moorings.....this was a red one on the right side of the tone board. When I was satisfied I couldn't see anything else amiss I powered up and was pleased to hear dire straits coming from the 2 speakers I have connected. So far so good.
Did you count hours?
Manhours spent.........well I started this almost a month ago, this is not a full time thing of course maybe a couple of hours most nights with a bit more effort at weekends. Its not finished yet and looking at what is still to do I would estimate the same again before I'm done, the cost of employing an engineer to tackle this would be very high, but where would be the fun i that...as Peter points out it's probably not the best receiver B&O ever produced but it is very pleasing to the eye.
Decoder and relay trigger board next up.....
this board has picked up a lot of dust, removed the presets to get at it and with the exception of one well hidden cap all went well
Back in place.....need to refit the presets and choose my next target
I did have the 6000 repaired when I bought it and have found the repair bill from 2002 when it was done. It needed 4x220 Ohm presets, 8x 0.12 Ohm 2.5W resistors7x 12v wedge lamps and 1 sundry!! The parts bill was £23.20 and the labour was £54. Including VAT, the bill came to £90.71. I'll keep it for you and you can have it along with the Beocord 5000 when I see you next! The work was done by the services department of J.G.Windows and they would essentially try to fix anything and I am sure did some things for the love of it and charged me very little. It has to be said that they drew the line at the Beocord 5000!
I recognise the presets and wire wound resistors from the power amp...the lamps will be from the illuminated ribbon indicators...wonder what on earth the "sundry" was all about. Its a shame such service departments no longer exist, at least not that I know of....we had a McKenna & Brown store in Stockton that was the Sony agent....they had a cracking service department over the river in Thornaby, very knowledgeable engineers.
I have replaced the presets and indicating levers but found a spacer in the bottom of the casing and have no idea how it goes back in, had the devil of a job getting the presets in actually, until I realised that the fixing bracket holding the wheels slid back and forth......so will need to figure out where the spacer goes....in the meantime the EL Switch PCB is next in line.......lots of dust here with it being on the top, there is also footprints in the form of white jumper leads that have been part of a previous repair.
Switch board all cleaned up and caps replaced