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
Dear fellows,
I acquired my first pair of Pentas yesterday. Mk 2 Beolabs. They're in excellent cosmetic condition - no rot!
The original mains cable is cut short and terminated in a plastic 'block connector'.I phoned B&O in Bristol to check which fuse I should use in the plug I attach to the open end of the block connector - the guy on the phone said a 5 AMP fuse will be fine.
I plugged one of the Pentas into the mains with a 5 AMP fuse in the mains plug, no problem, the speaker's red LED came on and it sat in stand-by.I plugged the other speaker in the same way, the red LED came on but immediately went out. I'm unable to get any life out of it.
After reading through some of the Penta-related topics on here I decided to check the fuses on the underside of the amp. These appear to be a little bit corroded (white powder) but seem to be in ok health.
Can anybody help suggest anything else to try?The one Penta which is working sounds glorious and I'd love to enjoy a stereo set!
Kind regards in advance,
Julian
Hi Julian, I'd check for cold solder joints, had a similar error and after soldering helped in my case. regards
I'm not entirely sure but should not it be as you describe. Try to remove all the white and solder again. It should help. Can you make a photo and attach here. regards
Jan
Ok I forgot how frustrating it is to pop a photo up here. Basically I've swapped the fuses from the working Penta amp to the one which wasn't working.When I plugged it into the mains the red LED lit once again but then went out after a second.
I'm going to go and buy some more fuses and try again.
As for spotting dry solder joints I'm slowly trying to work out how to take the front panel off - tis tricky.
Ha! I found the "add file" bit in my profile...excellent idea.
Here's the fuse photo.
Quick update: a short trek around north Kent revealed that the T40mA fuse is rare to say the least so I'm going to have to order some online.
Can't really work anything out until then sadly.
If the 40 mA fuse blowns, then probably the 7815 or 7915 is shortened.
A 50mA fuse will do fine.
//Bo.A long list...
A 20mm fuse with 40 mA isn't rare at all. More challenging is to get an 30 mm version (100mA), which is used in the States or Canada with 110V here in Europe.
Take a slow blow, not a fast acting version.
Also, if it has now blown the same fuse twice, there's no sense in blowing more of them, that's not going to make the speaker work. At least try to find the actual problem first.
--mika
Beobuddy: If the 40 mA fuse blowns, then probably the 7815 or 7915 is shortened.
Um. What's that then?
Beobuddy: A 20mm fuse with 40 mA isn't rare at all. More challenging is to get an 30 mm version (100mA), which is used in the States or Canada with 110V here in Europe. Take a slow blow, not a fast acting version.
No perhaps 'rare' was the wrong word to chose. They're not available from any of the electrical retailers in my home town.
tournedos: Also, if it has now blown the same fuse twice, there's no sense in blowing more of them, that's not going to make the speaker work. At least try to find the actual problem first.
Thanks,
I needed to replace the fuses in the one which works so I can get back to having a reference speaker
Update:
This afternoon I bypassed the amplifiers in both speakers and connected speaker cable directly into the binding posts at the base of each column.The speaker which was previously working responded well - I'm listening to it now. Lovely and punchy!
However, the speaker which blew the fuses is still silent. I suppose this means the fault lies on the crossover - somewhere deep inside the cabinet??
I'm going to go deep - I'm heading in to explore the inside and to inspect the crossover.
I hope to find a popped capacitor, or something else obvious as to why I'm not hearing anything at all when bare speaker wire is connected to my BM6500.
If anyone can make any helpful suggestions please do - I've not been in a Penta before
Those are + and - 15 volt regulators. They are called IC5 and IC6 in the schematics.
I suppose it could also be the bridge rectifier at fault. I guess the only way to know is to open it up and measure some voltages around there.
/ Johan
pepps: If anyone can make any helpful suggestions please do - I've not been in a Penta before
Well, you need to open up the base and pull the two pcbs out. On some versions (perhaps all?) some inductors seem to be under dimensioned and fail.
Though, the blown fuse is probably a fault in the amp and not the crossover.
Johan: Those are + and - 15 volt regulators. They are called IC5 and IC6 in the schematics. I suppose it could also be the bridge rectifier at fault. I guess the only way to know is to open it up and measure some voltages around there. / Johan
Thanks Johan,
Am I risking my BM by connecting speakers directly to these two binding posts?
Johan: pepps: If anyone can make any helpful suggestions please do - I've not been in a Penta before Well, you need to open up the base and pull the two pcbs out. On some versions (perhaps all?) some inductors seem to be under dimensioned and fail. Though, the blown fuse is probably a fault in the amp and not the crossover. / Johan
Hi Johan,
The T40mA fuse blew, which is the display fuse not the amp one, so I'm not sure if there's a fault with the amp itself. Although I'm an utter novice at electronics so I'm trying to learn as I go.
I'm confused as to why one is working and the other not.
pepps: Am I risking my BM by connecting speakers directly to these two binding posts?
No, that should be fine. But there's no point doing that now that you've concluded that there's no sound. Open up the faulty speaker and have a look at the crossover boards.
Johan: pepps: Am I risking my BM by connecting speakers directly to these two binding posts? No, that should be fine. But there's no point doing that now that you've concluded that there's no sound. Open up the faulty speaker and have a look at the crossover boards. / Johan
Just doing a little research to find out how to do just that. I presume the crossover is behind the mid-range drivers...
pepps: The T40mA fuse blew, which is the display fuse not the amp one, so I'm not sure if there's a fault with the amp itself. Although I'm an utter novice at electronics so I'm trying to learn as I go. I'm confused as to why one is working and the other not.
It still powers all the control circuitry and preamp stuff. It's just the power section of the amp that's powered through the bigger fuse.
pepps: Just doing a little research to find out how to do just that. I presume the crossover is behind the mid-range drivers...
No, in the bottom. You need to open it where the binding posts are. Then pull out the boards, noting where the wires connect.
Johan: pepps: Just doing a little research to find out how to do just that. I presume the crossover is behind the mid-range drivers... No, in the bottom. You need to open it where the binding posts are. Then pull out the boards, noting where the wires connect. / Johan
I was too impatient
I found out there's nothing behind those midrange drivers but a nice piece of padding.Damn these things are so beautifully made!
OK I'll go back to the bottom end and open from there.
Thanks Johan
I hate to admit this, but when I connected directly to the binding posts hidden away under the Penta amplifier wound the collar onto the plastic sheath of the speaker wire by mistake.
DOH!!!
Having spotted this as I was attempting to get to the crossovers I've corrected my stupid mistake and am now relishing to some Radiohead in STEREO!
Damn these speakers sound so good even without the amplifiers!
I'm going to enjoy them like this for a while before I work out how to get the amplifiers sorted. I mean I suppose they should both have a service before I put them to work.
Thanks Johan and everyone else for the tips.
I'm so happy right now!
Good to hear. Happens to the best of us.
A blown 40 mA fuse and no sound coming bare connected penta's doesn't make sense.
Also no sound at all coming from all the drivers doesn't make sense either. One PCB in the bottom handles low and high range and the other PCB handles the midrange. So if 1 board fails, there should be sound from the other. Unless there has been someone before and did some tinkering.
And also mentioned earlier, a blown 40 mA fuse will only happen if there is a short in one of the components directly behind it. Rectifier at the bottom or at the display, or the LM7815/7915. Less likely is an opamp.
But as you've mentioned as a "novice", the penta isn't the most service friendly as you have to take out the transformer, which sits very precise in place.
Ok, just read your latest experience...
Leaves the task to service the amplifiers.
Beobuddy: Ok, just read your latest experience... Leaves the task to service the amplifiers.
Yeah Beobuddy, the amplifiers still need some love - but these columns sound so damn good as they are I'm going to chill out for a few weeks
Seriously, in the past I've had 1702s, 2702s, 3702, Beovox RL3500, Beovox 3000 (flat panel) and even (Celestion) Ditton 44s but these Pentas wired straight with no power amps are just superb! The music is literally floating and dancing in front of me - such an incredible soundstage!
Ok, ok I'm a little smitten. Better stop yabbering