General Forum

Re: More Penta III issues

Keith Saunders — Sun, 20 Apr 2008 11:34:11 GMT

Andy,

No apologies required, you rightly corrected my "British English", it is a fact that more people these days actually speak and write "American" English, so I often feel I should use it when communicating with an English speaking person outside Europe to ensure my response is not mis-understood.

Re: More Penta III issues

Jandyt — Sun, 20 Apr 2008 11:11:09 GMT

I stand corrected! Please accept my humble apologies

Re: More Penta III issues

Keith Saunders — Sun, 20 Apr 2008 08:25:55 GMT

As a courtesy to our non "British" English speaking members, I used local spelling !!

Our friends in places such as North America & Australia do use "Fluxuations" when discussing electrical disturbancies instead of "Fluctuations".

Even in the Collins "British" English dictionary it does provide "FLUX" which means:-

Flow or Discharge
Continuous change; instability
A substance such as borax or salt that gives a low melting point mixture with a metal oxide to assist fusion
The rate of flow of particules, energy or a fluid, such as that of neutions or light energy
The strength of a field in a given area; magnet

Re: More Penta III issues

joeyboygolf — Sun, 20 Apr 2008 01:49:26 GMT

Jandyt:
Fluxuations Keith!!!!!! tut tut tut

Keith knows what he means.............how's the De Lorean going???

Re: More Penta III issues

Jandyt — Sat, 19 Apr 2008 17:39:10 GMT

Fluxuations Keith!!!!!! tut tut tut

Re: More Penta III issues

tournedos — Sat, 19 Apr 2008 07:28:03 GMT

stevequinn:
Presuming this was the problem all along, has anyone any ideas 'why' D6 would have failed?

Common semiconductors like 1N4148 are used by the millions, and a lot of research has gone to their failure mechanisms and how they can be avoided. Power surges, static electricity, moisture and heat, among others, can kill them, and they may also fail prematurely if they are used too close to their maximum ratings (a design error, or more likely, a financial error while designing). Still, every now and then components can and will just fail for no particular reason. This diode in your Penta may have just been a victim of bad luck

Re: More Penta III issues

Keith Saunders — Sat, 19 Apr 2008 07:17:41 GMT

Steve,

Very pleased to noted that you have managed to get the Penta going.

With regards to D6 failing, as with any electronic component, they can fail for a number of reasons including:-

Bad circuit design which nearly always results in the component and associate components becoming known as common failures.
Bad manufacturer of the original component.
Overheading during assembly and/or repair. Remember leakage current across the junction doubles with every 1 degree in temperature. (Kirchhoff's law)
Lots of power fluxuations over a period of time.

With regards to your problem with PCB22, even if you know which component has failed without a surface mount removal tool, there is no way for you to replace the component. If the faulty component were defined you could take the board to a local electronics firm with surface mount extraction equipment and get them to remove and replace the device for you.

Re: More Penta III issues

stevequinn — Sat, 19 Apr 2008 06:40:06 GMT

Keith and others,

After replacing a number of capacitors and having no joy I measured some voltages again around the PCB1. I noticed that the voltage was low around TR3, so I desoldered it and to my amazement the amp came good! Looking a little further, I decided it had to be D6 'leaking' to ground. Luckily this is a common N4148 so I scavanged one from an old UPS board in the shed and after a bit of measuring and resoldering away she went. So far so good the Penta seems to have come alive again! (after many many frustrating hours of cursing and fiddling)

Presuming this was the problem all along, has anyone any ideas 'why' D6 would have failed?

And after all that one of the displays no longer works. I have traced the issue to the Ínput control' PCB22 which sits on top of PCB1 - I swapped that board with the other Penta and the display worked, so has to be a problem in PCB22 somewhere - they are all surface mount components...

Again, any thoughts welcome

Steve

Re: More Penta III issues

Keith Saunders — Wed, 16 Apr 2008 02:34:35 GMT

Steve,

Also check the Zener diodes D7 & D8 because if one were faulty, then the signal at pin 3 (right) and pin 11 (left) could become low resistance and effectively join the two signals. The best way to test these two zener diodes is to measure the voltage between signal ground and pin 7 of IC2 which should be (minus) -7.5 volts and on pin 14 of IC2 should be (plus) + 7.5 volts.

If the voltages are correct, then replace IC2.

Re: More Penta III issues

stevequinn — Tue, 15 Apr 2008 19:15:14 GMT

Thanks Keith,

Your descrition of the switching IC is useful. I have sourced one of these ICs for 90 cents and along with more capacitors I will persevere with replacing components. It's a bit unscientific, but hopefully I'll hit the problem by elimination.

I took voltage readings as per the scematic and all was correct, so remains a mystery why the amp is not operating.

Perhaps your suggestion that the left / right switching issue could be the IC1 might be a clue - the fault with the Amp does appear to be in the input stage somewhere.

When the Amp is first powered on it is slightly louder and then quickly fades to a whisper compared to the 'good' Penta. I have tried both the powerlink and RCA inputs. Next I want to test the speakerlink input, as from what I can tell this feeds more directly into the main amp circuit...

To add to all the headaches, the display on that speaker has stopped working now, and it is not the fuse...

Steve

Re: More Penta III issues

Keith Saunders — Mon, 14 Apr 2008 02:01:08 GMT

Steve,

In answer to your question "should the mode switch, when set to Left, only process the left signal" the answer is YES.

I have looked at the circuit diagram and the default for the circuit is the right channel. What I mean here, is if the switch was completely open circuit the right channel would be selected.

There is a fairly complex circuit for switching for left/right switching, its not a simple using the switch to feed the incoming signal. The switching itself is achieved via a standard 4066 line switch IC.

From your description it sounds like you have a fault in the line switching circuit and it maybe that both left and right are selected at the same time. If this is the case it would effect both speakers, but the fault would be in one speaker.

From the circuit below which controls the switching IC, the right channel is select when the emitter (one with the arrow) of TR4 is at +15 volts and the left channel is selected when the emitter of TR5 is selected.

The output of the above circuit at the junction of R13/R14 (Right channel) and R15/R16 (Left Channel) is the signal which actually triggers the 4066 line switch IC below

The top electronic switch is the right channel and the second one down is the left channel.

Re: More Penta III issues

stevequinn — Sun, 13 Apr 2008 17:38:59 GMT

Thanks Keith,

the question I have is should the mode switch, when set to Left, only process the left signal - because what appears to be happening is that regardless of whether the switch is set to left or right, the same sound signal is coming through the speaker. I disconnected the left signal wire inside the plug, and still the switch does not change the sound at the speaker - the right channel is playing in either left or right position... When both signal wires are connected the amp appears to be mixing them together, so when the balance control on the beocenter is on full left or right both speakers fade slightly...

Otherwise the switch is operating correctly: off is off and auto powers on the unit only when a signal is present. Left and right power on via the beocenter relay.

Re: More Penta III issues

Frank Rizzo — Sun, 13 Apr 2008 10:24:31 GMT

Hi guys....are the complete amp boards available still?? I've still not sorted out the problem with my penta 2's.....

Thanks..

Re: More Penta III issues

Keith Saunders — Sun, 13 Apr 2008 09:14:06 GMT

Steve,

If you are actually talking about the "mode" switch then the following should help:-

Once connected to the mains supply, the Beolab Penta is in the stand-by mode. The stand-by mode is indicated by a red light on the front of the amplifier unit. The speaker switches on automatically when it receives a signal, unless, of course, the MODE switch is set to OFF. When the speaker switches on, the light on the front of the amplifier turns green.

Set the MODE switch to either

AUTO, L (left) or R (right): Sockets POWER LINK Left speaker right speaker
SPEAKER LINK Receiver without built-in loudspeaker relay
Receiver with built-in loudspeaker relay
LINE IN MODE switch LR AUTO -- L / R -- AUTO

When the signal disappears, the speaker automatically switches off, i.e. reverts to the stand-by mode, after a delay of approx. 10 seconds (MODE switch in L or R position) or approx. 3 minutes (MODE switch in AUTO position).

More Penta III issues

stevequinn — Sun, 13 Apr 2008 02:44:47 GMT

Hi,

More strange Penta behaviour.. I replaced a few caps in the amp board and it seemed fine again for all of that evening. Next morning I switched on and it was no longer working - I suspect a transistor may have failed so I'm ordering a new board (not ready for ICE just yet...)

Does anyone know how the input mode switch is supposed to work? On the other Penta I notice that the left-right position actually makes no difference to the signal being amplified. First noticed this when I adjusted the balance control on the BC9500 - both speakers are louder in the centre setting, and both fade slightly on full left or right. So I de-soldered the left channel wire in the DIN plug for the right Penta and now the balance works (I have a B&W passive temporarily standing in for the broken Penta), however it makes no difference whether the input on the Penta switch is set to L or R. I would expect that if the L wire is not present there would only be a signal coming through the speaker amp when the switch is set to R...???

I wonder if there is a problem with the input control board which is mixing the L & R signals - and perhaps this is what has caused the left Penta amp to fail? It doesn't seem likely to me, but perhaps someone here can comment?

Steve