Glitch
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This is a excellent guide …But the only problem is getting the blue wall plug…
Rubber or silicone hose might work instead. Using a metal “support” threaded into the frame will improve the odds of a long term fix.
Glitch
Being in storage doesn’t stop the ravages of time. The belts will simply degrade. The Beogram belt has likely dried-up and/or stretched. The Beocord belts likely turned to “goo”.
The belts are easy enough to find from you favorite auction site or, if you are concerned about getting a good quality part, at beoparts-shop.com.
Instructions for opening the cases can be found in the service manuals or somebody here can walk you through. Taking pictures as you go can sometimes be invaluable to getting everything back together.
Be prepared for a sticky mess if/when you work on the Beocord. Cleaning up the belt goo residue is the hardest part of the job.
The belt replacement may not totally fix your problem. Some of the electrolytic capacitors may have gone bad with time. The good thing about doing the initial belt change yourself is that you can avoid the “belt goo surcharge” if you have someone else work on the machine ;-).
Glitch
Nice work. Really clean 4k you have there! I can’t wait to work through my BM4k. I have a BG4002 with CD4 built in and can’t wait to get the duo playing together one day.
Thanks! Don’t forget to post pictures when you get your duo working. I hope someday to have the same combo but am still waiting for the right turntable to come along. Glitch
The “right” turntable finally came along… It is a BG4004 in very good cosmetic condition. The dust cover has light scratches but no cracks. There is minimal wear on the keypad. Most importantly, when I opened it up, there were no signs of anyone being in there before. I’ve been able to fix what was broken, do some cleaning/lubrication and get it playing very nicely. My next steps will be to fully restore it to collector quality.
Evan: Hopefully this will provide you with some motivation to get your duo working 😉
Glitch
I’d like to get them working and use them again but wonder how practical (and costly!) this is.
Start by replacing JUST the belts, especially if you are concerned about the costs of repairs or how involved the project could be. That might be all that you need. It won’t be very expensive and only requires basic skills with a screwdriver.
It is always possible that there is something more seriously wrong. However, you really can’t start to debug any of that until the belts are working properly.
Glitch
I’d bet that you need new surrounds. However, I wouldn’t poke at it unless you are ready for it to fall apart.
I prefer foam since it is more likely to have similar characteristics as the original surrounds. The rubber seems to be more flexible, but weighs more. It doesn’t take much difference on something like a small, light midrange driver to change the overall performance characteristics. Rubber could sound just fine, but might not sound exactly like stock.
IMHO, working on the amps is an more forgiving job than refoaming the midranges. Getting the drivers perfectly centered isn’t straightforward. I suspect that many of the Penta DIY refoamed drivers would not pass the quality control of the original parts.
Glitch
The best way to proceed depends on what your goals for the speakers are.
If the goal is to get the speakers running at the same temperature (for piece of mind) at minimal cost, then simply adjusting the bias current would be a good place to start. Moving the trim pot during the adjustment might be enough to clean off any oxidation that might be causing the amp to run out of spec. The only equipment that you would need is a screwdriver and multimeter. I would build a cheap “dim bulb tester” for this. It is a inexpensive safety net that might avert any additional damage if things don’t proceed as expected.
Any competent service facility should be able to handle this if this is beyond what you are comfortable doing yourself. Aside from the unusual packaging, the Penta amps are pretty similar electrically to a lot of the other stuff out there. I wouldn’t get to hung up on finding a B&O authorized service center for this particular piece of equipment.
If you love the Pentas, they are definitely worth the effort to restore. The cap kits from beoparts-shop.com are a good place to start. Pentas are actually one of the better starter projects if you are interested in pursuing in this aspect of the hobby.
Whatever path you decide to take, I would address the overheating. The higher internal temperatures will degrade the components faster and eventually the amp will fully fail.
Glitch
It could be a couple of different things like a bad power filter capacitor or a trim pot for the amp bias circuit. It could also be a number of less likely things…
Are you thinking about trying to fix it yourself? If so, what kind of experience do you have and what equipment do you have access to?
Glitch
A quick google search finds one person claiming success using a TIP132/TIP137 combo. I recall seeing other stories where the person used something else on a BM901.
Another tactic is to use the published cross reference charts. That transistor might be old enough that you will have to cross reference the cross references. Verify that the specs (voltage range, gain, etc.) are similar to that of the original part.
A “close enough” part won’t necessarily perform exactly like the original.
I’ve only had to do this with final stage transistors a couple of times. Hopefully, someone with more experience, or experience with this exact situation, can chime in with better advice.
Of course, Martin’s advice of replacement using the correct parts with a procedure that won’t damage them is the best way (if you have the necessary equipment).
Glitch
You might want to consider using modern, readily available transistors while you are trying to sort out your failing transistor issue. This could save you a significant amount of money versus installing rare and expensive vintage transistors. This is especially true if you use the trial and error methodology.
I keep a fairly large supply of cheap Chinese parts on hand for this purpose. I’ll swap them in as part of the debugging process. Once I have the circuit working, I’ll replace them with either high quality modern parts or (expensive) original vintage parts. What I do depends on my goals for the particular piece of equipment.
Glitch
It wears out the motor brushes instead.
Good point. The brushes certainly wear out (and don’t appear to be a serviceable part).
Glitch
But it does seem strange behaviour to me, and can’t do much for prolonging component wear.
For some bearing technologies, the highest wear occurs when the mechanism starts. I think that this is because motion is needed to create and maintain an oil film. Bearing wear is negligible after the bearing reaches equilibrium. B&O probably made this design decision in order to minimize wear.
Glitch
I assume that you are asking about the capstans?
I’m not familiar with the BC5500, but on other Beocords the capstan turns whenever the deck is not in standby.
Glitch
The good news is that the bad part should be easy to find ;-). Determining why it failed could be trickier.
It most likely can be repaired. You will need to open it up to be able to tell how involved the repair will be. Posting pictures of the problem area will make it easier for someone to help.
Glitch
The original caps have values that are not available anymore.
This is not completely true. A quick check of part-express.com will show that you can still buy capacitors that are marked the same as the original caps. One would have to measure the caps that were received to be sure.
There are a few other manufacturers of higher end caps that would likely have the original values (but you might have to wait a while for them to come into stock). The tolerances on these caps are very close to design, but are much more expensive.
In many of the other capacitor brands or product lines they will only make the values similar to what you have in your crossover.
I generally agree with premiumverum about the tolerances (assuming that the original caps were +-20% parts) and the sound.
I’d leave them alone if you like how they sound. Unless of course, that you like tinkering with things as much as listening to music.
Glitch
The former owner may not have been able to find the exact values and substituted the next closest values. Piggybacking the capacitors in parallel is one way of getting a value closer to the original.
Post a table of the installed values versus the schematic values. This will make it easier for those that want to help to give better advice.
Glitch
It looks to me that there are 10 bipolar capacitors on the schematic and “10” on the actual crossover board. I’m assuming that the two capacitors to the
rightleft of the “50” on the board are wired in parallel and should be counted as one.The other caps are (likely) the white boxes, yellow components and the electrolytic on the bottom of the board.
Glitch
You might also find some hints here…
https://beoworld.dev.idslogic.net/forums/topic/my-beocenter-9500-restoration/
Glitch
Ears are notoriously untrustworthy – they’ll blindly believe anything they hear! ?
Isn’t the problem actually the brain? (i.e. Psychoacoustics) 😉
Glitch
I’m still undecided what to do with the crossovers. Just take the service kit from Martin or maybe do the improvements suggested by Die.Bogener? What do you think?
You might want to measure your existing capacitors and go from there. The caps that came out of my Pentas measured very well. I had some caps (leftover from another project) that I swapped in as an experiment and I couldn’t tell any difference.
I subscribe to the theory that the majority of improvement that comes from recapping crossovers comes from having better matched components. This is in contrast to those that believe that one capacitor sounds better than another. Speakers with well matched crossovers image better than those with mismatched ones. IMHO, this is easier to notice than a minor change in frequency response.
You might want to consider measuring, sorting, and repositioning the mid-ranges. This in in the spirit of having better matched speakers. Doing this noticeably improved my Pentas.
Glitch
