The Workbench

Re: Burned resistor Beolab Penta 1

tournedos — Thu, 06 May 2010 01:32:36 GMT

The displays themselves are all totally different, but they are all almost directly connected to the various (datalinked) inputs. The amp doesn't have much to do with them expect that it supplies the power (and maybe lights up a LED or two, I haven't looked that closely).

So, I guess it would be possible after checking the wiring pinouts and the supply specs, but where are you going to find the displays?

Re: Burned resistor Beolab Penta 1

lausvi — Thu, 06 May 2010 00:26:28 GMT

Leslie:

Other thing, I want to exchange the yellow led's with green or red

BTW, is it possible to replace the displays between the MK1-3 models? I have MK1 Pentas, can I put a MK3 screen in? (My BC9000 is so high that I can't see which track is playing and the MK1 displays don't show that.)

Re: Burned resistor Beolab Penta 1

Dillen — Wed, 05 May 2010 16:58:06 GMT

Sorry if I haven't replied yet, I am extremely busy at present.
The capacitors you found are probably fine though I like to mount
105deg types because of the quite warm location inside the amplifier,
right by the transformer. A little bit more costly but worth it for
the considerably longer lifespan.

An amplifier kit exists that also upgrades to Burr-Brown Opamps and MKS-2 foil caps
in the signal path but I have no crossover kit for this Penta version, mainly because
I never noted a demand for one.

However, I suggest you have the current faults diagnosed and repaired before
eventually upgrading to avoid the risk of introducing additional issues that could
make it all harder to fault-find.

Martin

Re: Burned resistor Beolab Penta 1

Leslie — Wed, 05 May 2010 16:09:15 GMT

Thanks! Good advise not to do, this is technical knowledge that I don't have.

Much appreciated, stays yellow!

Re: Burned resistor Beolab Penta 1

tournedos — Wed, 05 May 2010 16:04:50 GMT

Leslie:

Other thing, I want to exchange the yellow led's with green or red

I have a faulty MCP5500 board which has lots of red and green leds on the display board. I suppose I can use these instead?

The problem with this swap is that different colour LEDs have different threshold voltages, or voltage drops over them. Unfortunately yellow is the highest of these, so if you simply replace them with green or red LEDs, they are going to get more current than was originally designed.

Without looking at the schematic and doing some calculations, I can't say how close that would get to damaging the LEDs or the circuits driving them, but there's always the chance. And there are quite a lot of LEDs, so the power supply of the display board might get overloaded as well.

Re: Burned resistor Beolab Penta 1

Leslie — Wed, 05 May 2010 15:42:52 GMT

Other thing, I want to exchange the yellow led's with green or red

I have a faulty MCP5500 board which has lots of red and green leds on the display board. I suppose I can use these instead?

Re: Burned resistor Beolab Penta 1

Leslie — Wed, 05 May 2010 15:38:37 GMT

Ville Laustela:

I thought I had a photo of the display board but can't find it! I think there were some 2-4 small caps and one bigger one, one of those golden-coloured ones.

I bought my bipolar (and other caps) as a kit from Martin - all parts there and good instructions, as always.

This one?

Btw, a friend of mine (Beoworld member Ger) is looking for a display board. Anyone?

Re: Burned resistor Beolab Penta 1

tournedos — Wed, 05 May 2010 15:32:34 GMT

Silly me, it even shows in Leslie's picture (and one of the service manuals on site.)

No way getting round it then, you'll need a 220u cap. The later crossovers are so different that the upgrade wouldn't be just the swap of a couple of component values.

Re: Burned resistor Beolab Penta 1

Leslie — Wed, 05 May 2010 15:30:59 GMT

Check 2nd picture I have posted whee you can see this specific capacitor.

So, Martin, this can be another value?

BTW, I have replied on your PM regarding the Amplifier kit capacitors but still no reply back from you. Maybe you've missed it?

The 10000uf found here, same brand bit thicker and much shorter.

tournedos:

Where did you find a 220 uF bipolar? There shouldn't be any, the biggest caps on the crossovers are 68 uF. I wouldn't go below a 100V rating, there might be problems when you put the power capacity of the Pentas to use...

I hear those large caps for the amp power supply are hard to find, almost anything commonly available is physically too large.

PCB14 C2 (6601 Penta)

http://cgi.ebay.de/ws/eBayISAPI.dll?ViewItem&item=270510432501&ssPageName=STRK:MEWAX:IT

Original size 30x95mm?

Re: Burned resistor Beolab Penta 1

lausvi — Wed, 05 May 2010 15:28:59 GMT

I thought I had a photo of the display board but can't find it! I think there were some 2-4 small caps and one bigger one, one of those golden-coloured ones.

I bought my bipolar (and other caps) as a kit from Martin - all parts there and good instructions, as always.

Re: Burned resistor Beolab Penta 1

Dillen — Wed, 05 May 2010 15:23:25 GMT

I agree on the tweeter/resistor and display comments but indeed, the earliest
version of Penta had a couple of 220uF/100V bipolar capacitors in the crossover filters
at the woofer/tweeter board.
Looks like a desperate attempt at getting the circuit to work and it was revised
already in the next version.

Martin

Re: Burned resistor Beolab Penta 1

tournedos — Wed, 05 May 2010 15:14:06 GMT

I'm sure you could hear the change, but the difference maybe won't be dramatic (it was on my RL60.2's...). Easy to do sometime later anyway once you get the more serious problems sorted.

Where did you find a 220 uF bipolar? There shouldn't be any, the biggest caps on the crossovers are 68 uF. I wouldn't go below a 100V rating, there might be problems when you put the power capacity of the Pentas to use...

Probably well worth replacing those caps that Ville mentioned on the displays.

I hear those large caps for the amp power supply are hard to find, almost anything commonly available is physically too large.

Re: Burned resistor Beolab Penta 1

Leslie — Wed, 05 May 2010 14:46:23 GMT

Wow, Suomi.... Have lived there for a while

I'm not an audiphile listener so actualy no need to replace these caps is it?

On the other hand its not that costly to replace them.

Funny thing though is that I can find all the bipolair caps on the Internet except for the one with the 220MFD/100V value.

Is this an obsolete value and is 100V for the capacitors a need or can it be less?

Will check the display's capacitor, justed wanted to have another colour.

It seems that capacitors generally causes faults in circuits by age. I found one in a LC2 (for sale now, be honest) which I have replaced and in full working order now. My first repair that I did myself (mighty proud)

Paljon kiitoksia guys!

Re: Burned resistor Beolab Penta 1

lausvi — Wed, 05 May 2010 14:31:53 GMT

Leslie:

Last question is that I want to replace the 7 segment displays (5 pcs each) because the intensity is not that what it's used to be.

In my Pentas there was a big electrolytic capacitor in the display board that was running very hot and had already leaked a bit. If that's partly shorted it could (?) cause the displays to be dimmer than they should.

Re: Burned resistor Beolab Penta 1

tournedos — Wed, 05 May 2010 14:13:49 GMT

Leslie:

No technical support at all? This subject has been put in the right section has it (Workbench)?

Too many questions in one post I suppose - I read your post earlier but didn't have time to answer...

I'll start with the displays. LEDs don't dim with age. Either they are actually just the same brightness they were when new, or there is something else wrong in the circuit. I believe the display windows were replaced with lighter ones at some point of the Penta lifetime, due to visibility problems?

The burned resistor indeed belongs in the tweeter circuit, and your tweeter seems to have a blown voice coil. Perhaps the resistor shorted first and let too much power to the tweeter taking it out as well, or more likely they both were damaged by a severe overload at the same time.

On the crossover boards, you'd need to replace all those gold coloured caps. Their condition can't be judged from the outside - they don't usually outright fail, but the characteristics get worse with age. You don't have to replace any of them, but it would most probably make a clear improvement in sound.