Steve,

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

• 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).

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

Thanks..

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.

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.

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

Steve

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.

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

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.