BeoLab Penta 1 Speaker Amplifier Base getting very hot

[xcrounse]

I am the original owner of a BeoMaster 5500 system with a pair of BeoLab Penta 1 tower speakers. Recently, the base (amplifier) of one of my speakers is getting very hot during use. It is running considerably hotter than the other speaker. The speaker still sounds fine. It just gets hot. I’m afraid it might catch fire or fry all the electronics. Is this a common problem? Any ideas on how to fix? I live in the Seattle area and there are no authorized B&O dealers. Closest are in California. Any help would be appreciated.

[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

[xcrounse]

Glitch, thanks for your response. Although I am savvy in all things digital, I’m certainly no expert in electrical engineering. I’ve watched some YouTube videos and learned a lot about the BeoLab Penta and issues like foam degradation in the mid-range speakers. I haven’t pulled off the grill to examine that issue, although the speakers still sound great to my ears. I’ve mitigated the overheating issue somewhat by reconfiguring my cable connections from my stereo amplifier. I switched from using the in-line audio jack connection on the speakers (that was over-driving my speakers) to using the hard-wired connection option. I also switched the sensitivity selection on my speakers to the minimal setting. I also blew out and vacuumed the vents on the speaker amplifiers.

The right speaker is still running warmer than the left, but I don’t feel like it is getting so hot that it will fry the electronics or catch on fire and neither speaker is defaulting to “yellow light” warning. Your thoughts? Unfortunately, there are no authorized repair options for B&O in the greater Seattle area.

[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

[xcrounse]

Glitch, thanks once again for sharing your knowledge with me. It’s not often that someone will take time to share their wisdom with a stranger. I especially appreciate the link to beoparts-shop. Whether I decide to dive in myself or hand this project off to an expert (if I can find one), the information you provided will be helpful. Replacing the mid-range foam looks like a do-able but time-consuming process. Seems each mid-range speaker would take an hour or more x 8. I don’t even know yet if I’ve got a foam problem, but I suspect after 30+ years there’s got to be some degradation. I notice both foam and rubber replacements are available. Do you or other experts have a preference? Once again, thank you so much for your correspondence.

[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

[xcrounse]

I’ll take your advice and not poke around too much. I might find things I don’t want to know about. I agree that addressing the hot-running amp is the highest priority right now. I came across a 5-hour video on YouTube from a guy named Dave who does a complete rebuild of the Penta amplifier. Amazing, but way beyond anything I want to attempt.

Again, kudos to you for your willingness to engage. Thank you!

[kronzilla]

Actually, refoaming surrounds is not that difficult. The smaller the speakers the more easy it is. It is little more difficult with de-centered spider of a woofer.

My first pair was with big Philips woofers, alot of patience and precise work, and they working perfectly, refoaming the midtoners are actually very easily to do.

Maybe after al these years, when you are busy, if you are adjusting the idle-current of the amplifier to the service manual, it is not a bad idea to check if the values of the other amplifier are the same. So the current of each speaker has the same value.

[Glitch]

kronzilla wrote:

Actually, refoaming surrounds is not that difficult. The smaller the speakers the more easy it is.

I used to think the same thing until I started measuring the performance of the drivers that I restored. It is pretty easy to make the drivers “look” better or sound better than with totally rotten foam. Matching the T/S parameters of a original/new driver or building a perfectly matched set is a different matter. I guess it all depends on what one’s goals and expectations are…

Glitch

[xcrounse]

Thank you, Glitch and Kronzilla. I truly appreciate your comments. I did find a technician who was able to fix the problem causing my speaker amp to overheat. He made some minor adjustments and replaced a “transistor”. Now the speaker is performing perfectly. I also had him examine my Beogram CD50. The CD tray wasn’t opening and closing as it should and my CDs would no longer play. His verdict was that the CD laser was too weak to “read” the CD and he didn’t think it would be possible or economically feasible to fix the player. Good think I digitized all my CDs years ago. Now, I have to decide if I want to sell the Beogram CD50 for parts or recycle it. It pains me to do this because cosmetically, the CD player is in nearly perfect condition.

[Glitch]

xcrounse wrote:

I did find a technician who was able to fix the problem causing my speaker amp to overheat.

That’s good news. IMHO, Pentas are worth the effort to keep running.

I expect that someone will provide good suggestions on what to try to repair the CD player. “Recycling” the player should be a very last resort. Any B&O gear has value, especially if it is in nice cosmetic condition.

Glitch

[kronzilla]

Actually, the laser us not dead. On the control pcb there need ti replaced some capacitoes with exact same value,low esr, Panasonic, Elna, Nichicon.. and maybe re-adjusting tle laser current a little bit. That is all. But you need a technician who can do it for the cdm4 laser. I had let it done for a cd5000 and a cd7000 and sounding like new. They had the same problem, reading problems. Thise lasers are extremely durable ( about 60-100k hours ( cdpro lasers lasting inly 6000h)and de sound is still natural, organic, with the grand dad if the dac’s ( philips 16bit tda1541) i would NOT suggest to set the current of the laser if you don’t kniw what to do. They are dead with esd-disharge. But they ladt very long, and the playets are build like a tank. AMark Levinson players are junk compared with these fantastic tank build technique 🤪

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