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Beolab Penta 6603 MK1 restoration project

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StuckE30
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StuckE30 Posted: Wed, Aug 20 2014 4:28 PM

I picked these up last Friday on a whim from a local classified ad. The woman selling them said they had been left behind years ago by a boyfriend and she wanted them gone. I went to look at them and was unable to test them, but cosmetically they were OK considering they were 28 years old (1986 production)

Midranges all had rotten foam as is to be expected. I offered her $100 for the pair and he gladly accepted.

When I got them home I hooked them up. One tower powers on, green lights and plays. It doesn't sound great kinda muffled, but all 9 drivers work.

The other tower green lights for a moment, then let out some magic smoke and amber lighted. I took the amplifier off and powered the tower externally. Sounds about the same as the other tower and all 9 drivers work.

I opened the amplifier and took a look inside. I noted a couple gate resistors that were cooked but nothing else visible. I found the 5a/250v slow blow fuse was blown so I replaced it and powered it back on with the power supply to the side so I could get a better look.

R99 and R100 both glowed red hot for 2 seconds or so before ghosting the fuse. During which time the only output is a steady 60hz (sounds to be) hum from the woofers.

I tore the amplifier the rest of the way down and started making a parts list.

The crossover boards are in good shape, nothing cooked but a few of the small gray resistors show cracking.

I ordered all new resistors and MKP caps to replaced the old dried up electrolytics.

Now waiting on parts :-)

 

 

 

Rich
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Rich replied on Wed, Aug 20 2014 6:01 PM

Good luck.  Keep us posted.

Blah blah blah, blah blah ba ran

StuckE30
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StuckE30 replied on Thu, Aug 21 2014 12:38 AM

I figured while I was ordering parts I would order a couple OPA2134's as well to replace the old op amps on the main board (1). I'm looking at the schematics and I'm not sure if I need to replace just one or both.

IC2 is a TL072CP
IC3 is a MC1458P

 

There is also another IC1 MC1458P on board (2)

StuckE30
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StuckE30 replied on Thu, Aug 21 2014 4:52 AM

I'm 99% confident in saying the IC2 / TL072CP is the only opamp in the audio signal path.... So I'm going to leave the MC1458's alone.

 

Lots of parts coming in from UPS tomorrow!

BO
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StuckE30:
I'm 99% confident in saying the IC2 / TL072CP is the only opamp in the audio signal path.... So I'm going to leave the MC1458's alone.

Correct! The others are for the auto turn on/off and for the protective switch off.

You should also replace the signal path capacitors , C1, C2, C5 & C25 to Wima film caps.

 


//Bo.
A long list...

Die_Bogener
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Did you replace the potentiometers? They are responsible for the "no load current" adjustment. If there is a defect, the transistors glow up...

Replace ALL electrolyth capacitors.

StuckE30
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StuckE30 replied on Thu, Aug 21 2014 4:39 PM

Thanks for the advice guys! I ordered every capacitor on the board EXCEPT the film caps, where can I get these red Wima film caps? Nevermind I see Mouser has them too they are just in a different category because they are film type!

 

All the electrolytics should be in today.

Yes I ordered new trimmer pots as well, I'd read that those dry out and help kill the resistors mine had glowing. Those should also be in today.

Søren Mexico
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Search the web for Wima capacitors, i get mine from Mouser.

Collecting Vintage B&O is not a hobby, its a lifestyle.

StuckE30
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StuckE30 replied on Thu, Aug 21 2014 5:03 PM

OK, ordered the red wima's from Mouser, they should be here tomorrow!

StuckE30
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StuckE30 replied on Fri, Aug 22 2014 4:07 AM

Most of my parts came in today from Mouser, all I'm waiting on now are the red Wima's.

 

 

I desoldered everything on board 1 that needed to come off, all the big resistors R99-R104, both trimmer pots, IC2 and all the electrolytics.

 

 

Close up of the new Burr Brown OPA2134 opamp that replaced the TL072CP.

 

 

I've got one question regarding the trimmer pots, what value should I set R59 and R95 to prior to powering up the amplifier to adjust them? Is that at all critical?

If I'm reading the service manual correctly I am to connect my DMM across R103 and R104 and adjust R95 till the DMM reads 30mv.... then adjust R59 until the DC offset at the amplifiers output leads is eliminated down to zero.

Dillen
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Dillen replied on Fri, Aug 22 2014 6:45 AM

It's always a good handrule to start with trimmers in center position.
The circuit will have been designed for a point not far from that.

DON'T use the markings on the board for capacitor polarity reference. They are not always correct! Actually, there
are quite a few typos and misprints in the silk-screen.
I normally advice to replace one component at a time, using the old component for polarity reference.
You probably have a good photo, that you can use for reference, that'll be fine too.

Anyway, I think, I would have diagnosed and repaired the bad amplifier module before upgrading and
replacing a lot of components.
If the new components doesn't cure the original fault, and you've inadvertently introduced a
new fault somewhere, it could end up a very difficult situation.
And in case the amplifier module turns out to be a complete write-off, you've lost money and time too.

Martin

tournedos
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tournedos replied on Fri, Aug 22 2014 8:10 AM

StuckE30:
all I'm waiting on now are the red Wima's.

Those are not electrolytic capacitors (and neither are the rest of the plastic foil caps regardless of external colour). Replacing them will do no harm, but most probably is just a waste of time. They don't age.

Keep the ones you removed, you'll need them somewhere else some day Smile

--mika

BO
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BO replied on Fri, Aug 22 2014 8:58 AM

tournedos:
Those are not electrolytic capacitors

Well, C1, C2, C5 & C25 (which are referred to) are actually electrolytic caps.

//Bo.
A long list...

StuckE30
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StuckE30 replied on Fri, Aug 22 2014 2:09 PM

Well its a little late to look at each component and replace them one at a time. I desoldered everything in one pass and then went back in to solder the new stuff in. I guess I will just have to cross my fingers and see what happens regarding the capacitor polarity. I did put them all back in according to the PCB silk screening. I have a few pictures yes, but I don't think any are sufficiently details to determine polarity of each component... but I do have the second working and unmolested amplifier I can look at. It only takes a minute to pull it off the other tower.

I'm pretty confident that replacing the trimmers and resistors is the problem, but that is based largely on experience I've seen with other identical units. Really I cannot *see* anything else bad, and I do not have the tools or experience to make a diagnosis beyond that.

While you have a point on the potential waste of money by throwing money at all new components in hopes it will just fix it... It's only $35 USD or so for the parts, and a little of my time. If it doesn't fix it I have no regrets, I've still had a bunch of fun and its a learning experience.

 

 

 

 

 

 

tournedos
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tournedos replied on Fri, Aug 22 2014 2:11 PM

BO:
Well, C1, C2, C5 & C25 (which are referred to) are actually electrolytic caps.

Oh, they are bipolars! Definitely worth replacing then.

Carry on, I'll get me coat Big Smile

--mika

Søren Mexico
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You should at least check rectifiers, diodes and the transistors, connected to the burnt resistors, I have never worked on pentas, but this kind of resistors are present in other amps, and I never found a bad one

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StuckE30
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StuckE30 replied on Fri, Aug 22 2014 3:25 PM

Well checking them would be nice... but I haven't the slightest idea what to check for. If anyone cares to teach and its something I can check with a DMM then I'm all for it. Otherwise I'm a risk taker heh...

 

During initial power up for setting the trimmer pots would it be "safe" to run the amplifier no-load without the fets snapped onto the heatsink? I suspect they aren't going to get hot and burn up if there is no driven load.... but then what do I know?

It's just a bit of a hassle to stuff all the contents of the heatsink housing back into it, especially if its just going up in smoke again....

Rich
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Rich replied on Fri, Aug 22 2014 6:16 PM

StuckE30:

If it doesn't fix it I have no regrets, I've still had a bunch of fun and its a learning experience.

That's the spirit.

Blah blah blah, blah blah ba ran

Dillen
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Dillen replied on Fri, Aug 22 2014 8:35 PM

StuckE30:

During initial power up for setting the trimmer pots would it be "safe" to run the amplifier no-load without the fets snapped onto the heatsink?

Absolutely no!
They MUST have normal operating conditions.
The FETs will not blow but their HFE depends greatly on their temperature and anything you adjust without heatsink
you'll have to do again with heatsink. - If you can get a stabile setting without heatsink at all, it's usually all over the place.

Martin

StuckE30
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StuckE30 replied on Sun, Aug 24 2014 12:14 AM

Pretty disappointed. Package showed up from Mouser a day late with the red Wima's, and the 10uf C25 caps are huge. Don't know how I missed them being 30mm lead spacing instead of 5mm like the others... oh wait its because Mouser didn't have the info filled in so it turned up in the same search criteria...

 

Sigh. Unfortunate as the cost of shipping the two replacements will be triple the price of the actual capacitors... that and no chance of getting this calibrated and tested this weekend.

 

Edit... and the ones I need are on back order. Seriously... Sigh.

 

StuckE30
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StuckE30 replied on Fri, Aug 29 2014 1:10 AM

The order of all the crossover components came in today. Its going to be fun to fit all these huge MKP caps into the space where the electrolytics were. Some of theses like the 68uF ones are HUGE!

 

StuckE30
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StuckE30 replied on Fri, Aug 29 2014 3:41 AM

PCB 15 as was original....

PCB 15 with the new resistors and MKP capacitors. Can you say OVERSTUFFED?

Leslie
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Leslie replied on Fri, Aug 29 2014 5:57 AM

Have you tried to put the cross-over board back in place with these enormous caps? Great thread btw.

Brengen & Ophalen

Dillen
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Dillen replied on Fri, Aug 29 2014 6:54 AM

The ceramic resistors need air around them.
Don't put anything too close to them, they can get very hot and heat is one thing foil caps don't like!

Martin

StuckE30
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StuckE30 replied on Fri, Aug 29 2014 2:22 PM

Yes actually I tried to reinstall that one board last night and noted that the large 68uF cap isn't going to work right there... I'm going to have to run longer leads and locate it off board. Same with the 2x 68uF caps on the woofer/tweeter PCB 14. Everything else layout wise is just fine though.

 

I'm still waiting on 2 red wima caps from Mouser to be able to test the amplifier, but I should be able to test the new crossovers/speakers with another amplifier this weekend.

 

I really appreciate the support guys!

Leslie
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Leslie replied on Fri, Aug 29 2014 2:54 PM

Can I ask how much you paid for the cross-over caps, they look quite expensive. Also wondering if you could connect MK2 or 3 displays on the MK1 Penta.

Brengen & Ophalen

BO
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BO replied on Fri, Aug 29 2014 2:58 PM

Leslie:
Also wondering if you could connect MK2 or 3 displays on the MK1 Penta.
As far as I know the interface for the displays are the same on all Beolab Penta speakers.

//Bo.
A long list...

StuckE30
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StuckE30 replied on Fri, Aug 29 2014 4:06 PM

Sure, here is a screenshot of the shopping cart of the order I put in through Parts Express.

The Audyn MKP caps are a bit expensive, and they are HUGE because they are all 400v. Lower voltage would have been a bit smaller but why not...

I actually noted although my Penta's are MK1 they have MK2 crossover PCB's by the part numbers. I noticed that when I was ordering parts and the repair manual listed all sorts of different values.

 

Leslie
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Leslie replied on Fri, Aug 29 2014 5:29 PM

Thanks Jordan, approx. 140 euro for a cross-over recap Penta pair with good quality caps. Maybe that will makes difference instead of using low quality caps. Will give it a try with my Penta 3's.

Brengen & Ophalen

StuckE30
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StuckE30 replied on Fri, Aug 29 2014 5:34 PM

Hey no problem! The P/N's are all there for you, but I would double check to make sure the MK2/3 crossover components are all the same. I only have MK1/2 service manual PDF's.

 

It is sort of unfortunate that Audyn doesn't make a 27uF capacitor so I had to break the nice matching kit with a Jantzen. Both are very very good quality though.

Dillen
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Dillen replied on Fri, Aug 29 2014 6:20 PM

StuckE30:

It is sort of unfortunate that Audyn doesn't make a 27uF capacitor so I had to break the nice matching kit with a Jantzen. Both are very very good quality though.

A tech note suggests replacing the 27uF with a 22uF...
Not all Penta Mk I are identical, they can be quite different and have different crossover filterboards.

And yes, Leslie, please do a test with these foil caps and compare to standard electrolytic caps.
I used to provide both a standard kit and a foil kit but to be honest I couldn't tell any difference and
so could none of the owners so the extra cost wasn't justified and the kit no longer made.

Let us know what you find.

Martin

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Beobuddy replied on Fri, Aug 29 2014 6:59 PM

BO:

Leslie:
Also wondering if you could connect MK2 or 3 displays on the MK1 Penta.
As far as I know the interface for the displays are the same on all Beolab Penta speakers.

The mk2 and 3 need a switch at the bottom to switch between an audio- or videomaster.

The brackets which holds the boards are different.

Leslie
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Leslie replied on Fri, Aug 29 2014 7:29 PM

Dillen:

StuckE30:

It is sort of unfortunate that Audyn doesn't make a 27uF capacitor so I had to break the nice matching kit with a Jantzen. Both are very very good quality though.

 

A tech note suggests replacing the 27uF with a 22uF...
Not all Penta Mk I are identical, they can be quite different and have different crossover filterboards.

And yes, Leslie, please do a test with these foil caps and compare to standard electrolytic caps.
I used to provide both a standard kit and a foil kit but to be honest I couldn't tell any difference and
so could none of the owners so the extra cost wasn't justified and the kit no longer made.

Let us know what you find.

Martin

I certainly will Martin, why spend to much if the result is less or none. At the moment I'm working on 2 pairs of RL7000's so comparison can be made. To make a comparison with just one pair of Penta's (left and right speaker) is quite difficult I guess. Send me a PayPal request for one pair of RL7000 and I let you people know the result.

 

Brengen & Ophalen

Leslie
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Leslie replied on Fri, Aug 29 2014 8:29 PM

Sorry Jordan for interrupting your thread. Please let us know the progress of your Penta restoration. Following it with much interest.

Brengen & Ophalen

StuckE30
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StuckE30 replied on Fri, Aug 29 2014 9:32 PM

It's no interruption, this is a discussion forum after all. We are all here to discuss things :-)

I hope to be able to finish the crossovers tonight and be able to do an A / B audition with the two towers run by an external receiver do hear the difference in the crossovers between the all original and the new and improved.

I just got an email from Audiofriends letting me know my midrange foam surrounds have shipped from the Netherlands. That shall hopefully be the last part. My wife is *starting* to question all of the speaker parts parcels and the costs of the contents.... ha ha ha...

 

Leslie
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Leslie replied on Fri, Aug 29 2014 9:55 PM

What about your speaker cloths, are they still okay?

Brengen & Ophalen

StuckE30
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StuckE30 replied on Fri, Aug 29 2014 10:01 PM

No, not at all. Many snags, tears etc. I'm not concerning myself much with cosmetics as of yet. Focusing first on getting them functioning as they should.

StuckE30
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StuckE30 replied on Sun, Aug 31 2014 3:51 AM

I finished up both boards, PCB 14 and PCB 15. I got them reinstalled into the housings, I did have to trim the inner stiffening ribs just a touch on one side to make enough room for the 2 68uF caps to nestle down in there. They are pinched between the baffle foam and the PCB so they are nice and secure.

Still waiting on those red wima's from Mouser so I screwed the base plate back on and connected the tower up to the Yamaha reciever I have out in the garage for car work tunes. Figure 50w rms @ 8ohm or so.

I have to say I'm impressed. The tower sound MUCH improved over how it sounded with the old components.

 

Now to finish the amplifier and get it tuned so I can do a true A/B comparison between the two towers.

Die_Bogener
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There is no need to use 2 of the 68uf caps on the one board. Only 1 of the two caps is responsible for the sound of the woofers. The other one is used for linearisation of the load for the amplifier.

Look at the circuit plan, you will see, that only 1 68uf cap is needed. To replace the linearisation cap with a MKP cap is a big waste of time, space and material... and money. It makes no difference for the amp using the cheap bipolar electrolyth cap in this position.

And there is absolutly no use of caps with 400V. The amplifier works with */- 40V, so 100V is completly sufficient. The Penta reaches it's 300W output with voltages less 100V. Usually caps with 160V fit perfectly with the size of the original caps. 400V does also not sound better, they are only more expensive. Since the boards become pretty warm, the heat dissipation can damage the caps easily, since there is less cooling space available. So it really makes no sense using 400V caps.

The pictures are still available in the old workbench forum how to replace the Penta caps... 

Replacing the 27uf cap is also quite easy. On the original position fits a normal 22uf cap, on the other side of the pcb fits a 4,7uf flat MKP type perfectly. It is also better, using 2 caps instead of just one, the internal resistence becomes even better.

You can read it in the archieved forum from 2007...

Die_Bogener
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This here is everything you need to improve the soundpath of the Penta...

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