I forgot today was a holiday so no mail service.  I'll have to wait until tomorrow to try out the new timing circuit components.

-Sonavor

Looks like one more day...the parts weren't shipped until today. I should have just gone over to Mouser and picked them up myself.

I received the parts today a few of each - IC6: 74LS393N, IC7 & IC9: 74LS93N  and the mod IC(x): 74LS74AN

Nothing to jump up and down about on solving the problem though. However, I did learn some things that I hope will eventually solve it.  As a sanity check I wanted to see clocks go through the IC6 -> IC7 clocking circuit that feeds the pin 15 (timebase) of IC4 (the processor). I setup a little test using a breadboard, a function generator, DC power supply and an oscilloscope.  The supply provided +5 VDC for the ICs and the function generator provided a 5 VDC square wave to test the counters.  My signal generator only goes up to 2 MHz so I couldn't run the test with 3.975 MHz as the actual Beamaster 6000 02 Module.  But the test reassured me that the ICs work and that I was be able to set my scope probe on several outputs of the ICs and see the clock signal.  I ended up testing my new ICs I bought as well as the ones I took out. They all ended up testing good on the breadboard. 

Unfortunately they still don't work installed in the 02 module.  The clock signal is only at the pin 1 input of IC6 - the starting point of the clock signal through the counters.  The output points in the counter circuit have no signal at all.

So I started looking for other reasons why. One thing I hadn't looked at close enough was the IC Vcc power (+5 VDC).  In testing the 02 module in the BM6000 today I noticed that the +5 VDC power to the IC4 processor is always a good +5 volts.  The +5 power on the clocking circuit is not.  It is usually down around +2.4 VDC...never above that I could see.  The clock input to IC6 Pin1 was around 800mV.  I measured a lot higher on the breadboard. 

The schematic shows that the IC4 processor has its own power supply.  The +5 VDC for other components on the 02 Module get their supply from a different connector - P2-1 and P2-2.  It comes in as 6.5v and the TR1/TR2 circuit produces +5 VDC.  When I meausure the node where the TR1 collector, R1 and C2 (positive lead) all meet - I only measure 3.3VDC.  The resulting +5V side then measures around +2.4.  If I remove the 02 Module and try to just measure the 6.5v coming in on the P2 connector, I can't do it.  The unit won't let power come on.  I can't be sure this is the root of the problem but it appears to be the most promising right now since the counters worked fine on the breadboard where I supplied higher voltage.

I think I need to go through test the modules that source the power and see if I can determine what's loading down the 6.5v line. I'll have to first figure

-Sonavor

Good work so far, so easy to overlook the obvious! Why can't you measure 6.5v with the connector unplugged? This is not a switched circuit and should be energised all the time. Think you need to disconnect the volume board and first check the 6.5v supply on the PSU module.

Check the bridge on C1 in the PSU and make sure you put it on the correct terminal?

I'm not sure yet but when I disconnect the P2 plug and try to measure 6.5v in its pin 1 socket I am not reading anything. However, the P2 pins 1 and 2 tie together on the 02 module board, then go through a jumper. The voltage at the jumper is the same point I measure 3.3v so I disconnect one end of the jumper so I could measure the incoming P2 signal unloaded (by the 02 board).  That measured 9.7v. I checked that voltage with both my scope and a dvm. The schematic shows it should measure 6.5v so I'll have to start looking at the PSU module as you suggest. On all of the last few tests I have been running with the 02 Module re-installed in the receiver I only have the 02 Module connected to the connectors on the bottom of the board - to the power supplies and the keypad.  I have the connections to the 03 board, volume motor and FM tuner disconnected.

02 Module - IC4 processor works !!

I don't have the problem fixed yet but I have managed to see that the 02 Module will come to life.  With the 6.5v line from the P2 connector disconnected (via pulling the jumper on the 02 Module), I decided to try using my DC power supply to provide 5 volts there.  When I did that, the board came to life and the keypad could switch selected sources ... changing the display.  I could also switch it back to standby mode. I didn't take it past that since I don't have the 02 Module connected up to everything it is supposed to.  But that is a big relief.  It appears the odds are good that the 02 Module is fine and the problem is in the power coming in on the P2 connector. That 6.5v comes off the 10vac tap of the main transformer from what I can tell. Maybe I didn't get something there connected up correctly. Here are pictures of the 02 Module working with the external DC supply providing the 5VDC power to the board.

Module 16 (Power Supply) is the source of the 6.5v to the 02 Module.  The 6.5v doesn't connect directly though.  It is routed through the 06 Module (Motor Control). I disconnected the connector that carries the 6.5v from the 16 board to the 06 board and measure the value right at the 16 board connector (P41 pin 1).  There is pretty close to 6.5v volts there.  So something between that and the 02 board is interfering - must be the 06 board.  Next step is to test some paths out there.

-Sonavor

This is great John, we are following this thread with admiration, and barely concealed jealousie, your know how is a goal for all of us amateurs.

There are not to much replyes on your thread, but as you explain everything so clear, there is not to much to ask about, but you have until now some 1350 hits on your thread, so keep it up, I love it.

I spent more time working with the power supply this evening and I must have read a voltage wrong earlier.  As it stands now I am not getting 6.5VDC out of the Module 16 Power Supply. It is putting 9.9 VDC on its P41 Pin 1 coming off that board.  So it is the problem. The circuit for the 6.5 VDC from the service manual is shown in the picture here.  The values in blue are what I am measuring with the DVM.  The values in black are what the schematic shows as expected values.  I started pulling off the components and measuring them but I only found one component that differed from the schematic.  That was C7 which is listed as 470pF.  It measures 1.2pF out of the circuit.  Resistors R12 and R1 have charred areas under them on the board from heat I guess.  The two resistors measure pretty much right on though.  The R4 trimmer looked good (I pulled it out and measured it). Transistors IC1 (Darlington Pair) and TR1 don't have any shorts or opens. I will have to pull the two zeners and test them on a breadboard but from the measurements I am getting it looks like D2 is not doing its job.  it is supposed to hold 3.2V at the emmiter of TR1 but I am measuring 5.8V there.  The point between the D3 zener, C7 and R4 pot is 3.0V which is closer to the 2.7V value of the zener than D2 is to its voltage. The C1 electrolytic that I replaced at the beginning of this project still measures really close to its 3300uF value. 

The D2 zener and the C7 capacitor are the only two components that look like they might be bad.  I will see if I can round up replacements tomorrow for them.

I decided to mock up the Module 16 10VAC rectifier to 6.5V circuit in Electronics Multisim.  It isn't a perfect simulation because the components used in the model aren't 100 percent equal to the real thing.  But the simulation is pretty close to what I see on my Beomaster 6000. A picture of the simulation is below. It is confusing because the service manual has 6.5V posted on Module 16 connector P41 pin1 but I measure 9.9V and the simulation circuit has over 9V.  Yet when I can make that line just over 5V going into the 02 Module the processor circuits work.  There is something I am not seeing.

sonavor:

I will have to pull the two zeners and test them on a breadboard but from the measurements I am getting it looks like D2 is not doing its job.  it is supposed to hold 3.2V at the emmiter of TR1 but I am measuring 5.8V there. 

Not quite right - that zener has no reference to the ground, so it can't control voltages against the ground. All it can do is drop its rated voltage. Subtracting the test point voltages, I guess it is a 3.3V zener, so the difference of 9.9 - 5.8 = 4.1V is a bit suspicious and it might actually be bad. An error there will raise all other voltages (including the output).

This circuit is an adjustable voltage regulator. R4 is there to set the voltage. After you have confirmed that all components are fine, then go ahead and adjust it to output the rated 6.5V. I believe other test points will then follow. As to why it may have drifted... bad zener or bad trimmer.

I personally don't trust those trimmers at all at this age. At least work it back & forth a number of times to ensure it has contact. It may fall apart in the process...

I assume you tried tweaking that trimmer? I certainly wouldn't put the original back now you have removed it!

Well, I was planning to finish recapping my (working fine) Beomaster 6000, now I'm not so sure...

John, you're doing an excellent work (the photos are superb too), and this thread is having us panting!

Olly and Mika are very helpful as well!

But oh Martin, where art thou?

I missed that simulation, you must've posted it while I was writing my reply amidst having breakfast! It seems to make sense, try adjusting the trimmer in that first!

Oh, and I have forgotten to mention - I thoroughly enjoy threads with quality photos such as these have been! I know how much work it is to prepare and annotate them...

If someone with a Beomaster 6000 has time and a DVM could you measure the DC voltage between pins 1 (+) and 4 or 5 (gnd) on connector P41 of the Power Supply 16 Module?  If possible take the measurement with the connector on and with it off.  I would like to verify that the voltage on pin 1 on a good unit is 6.5 VDC. 

Meanwhile, I took time today to add the 06 Module circuit part that connects to the 6.5V line to the simulator.  Then I went back to my Beomaster 6000 and re-measured the voltages at all the key points. The new diagram below shows the 06 and 16 module circuits with the schematic listed voltages in red, the actual measured values in blue (and parenthesis) and the simulator calculated voltages in the various DVM boxes. On the new simulator I mocked up a voltage on the lower left to represent what I think is coming from the 08 Module.   

I did try two trimmers (16R4 and 06R11) on the receiver and on the simulator.  The 16R4 trimmer affects the base of TR1 but it didn't change anything else by much (both in the simulator and the real thing).  The 06R11 trimmer affected the base of 06TR2, the emitter output of 06TR2 and the collector of 06TR1 (TP17). From what I can tell 08 Module tuner circuit feeds a signal to the 06 board and the output is the signal going to c-D1 - 02 Module P5 pin 7.  That is the series of LEDs that indicate tuner signal strength I think.  So the 2.7V shown in the schematic is probably showing a normal (off ?) state.

In any case, the simulator values are closer to what I am measuring than what the schematic shows.  So that is confusing.  I'm going to take a break and hope some new idea comes to mind.

Okay....maybe it is ready to work now!! (?)

Going by the fact that the simulator pretty much matches the actual circuit when I make measurements and because I took out and measured the components involved on Module 16, decided to connect the 02 Module and keypad back up to the receiver....and it appears to work now.  With it hooked up and working I now am seeing 6.2V across Module 16 connector P41 pins 1 and 5.  So it looks like the destination circuit in the 02 module loads the 9.8 volts down to a working 6.2V. 

What changed?  Maybe taking apart and re-soldering the Module 16 components.  This is the first time I tried the 02 Module since investigating the power supply.  I still haven't reconnected the FM tuner board (08) or the volume/tone/tuning control board (03) so I'm not going to celebrate too much yet. 

I'm not sure how soon before I re-assemble everything.  I'm not going to rush anything.  But so far so good.

-Sonavor

Just to be complete...

I added the 02 Module part of the +5 VDC supply voltage circuitry to the simulator and measured everything again.  The simulator also saw the 6.5V line out of the 16 Module drop. I figured that since I had the voltage readings for the circuitry without the 02 Module connected and was confused by it - that I would do one with it in working mode. So the service manual schematics aren't in error.  They are values in an operating unit which makes sense.

In the picture below - the voltages I show for the measured and simulator values on the 06 Module are dependent on settings of the trimmers on the 08 Module (8R43) and the 6R11 trimmer. The relative differences in the voltages are probably pretty close but output to the tuning indicator is dependent on the signal from the 08 Module (through the 06 Module) and where those trimmers are adjusted to.  The voltages shown on the 16 Module and 02 Module should be pretty accurate for any Beomaster 6000 I think.  The service manual values are in red, the actual board measurements are in blue (and parenthesis) and the simulator values are on the DVMs.

One more thing - on the 16 Module measurements this time, I did adjust the 16R4 trimmer while monitoring the base of 16TR1 and set it to 3.8V.  I'm not sure if that is what I should have been monitoring.  Doing that changed the P41 pin 1 output from around +6.2V to the +7.02V I show in the diagram. 

Reassembly and test

I put a good part of the Beomaster 6000 back together tonight.  Enough so that I could check some operations of actually using it.  The power works and the receiver starts out in standby mode.  The remote control works (first time to try that part).  I decided not to use much power yet since I haven't adjusted the idle and offset voltages of the output section so I connected up some headphones. Starting with an ipod connected to the TP2 Play connectors I tested out the sound....sounds really good.  The volume, tone and balance controls are noise free.  I discovered a problem though.  As you can see in the pictures, the volume display is not lit.  There are two light bulbs and they did work before.  Since neither of them are working I am thinking it is a problem with the circuit that drives them.  I'll have to track that down tomorrow. I also ran a tuner test.  With the Beomaster connected to my house FM antenna the local stations are strong and very clear.  However, I discovered a second problem. While the tuner display is no longer stuck on 74.8, the display now jumps around.  When I first turn it on and go to the "P" tuner select the current station's frequency accurately displayed in the window.  After just a few seconds the display started cycling to different numbers.  When I tune the preset station dials the frequency display doesn't accurately show what I have tuned.  I am wondering if the clock signals have noise on them.  I'll measure them tomorrow.  I'm glad I didn't put everthing back together before testing it.  At least these current problems don't mean a dead receiver.

Yipee!

Maybe I'm stupid, but what did you fix exactly?

Well, I have never known such a troublsome unit before lol... I hope you replaced that trimmer, in fact might as well do the lot for what they cost, apart from the radio module. Seems you need to investigate the volume board however....

Regarding your tentative approach to power up you must be carefull here as things might not operate as they are supposed to, which gives missleading results.Use the thing wisely but IMO you shouldn't rely on it when testing unless there is an obvious loading problem! With concern to noload / offset just set those trimmers to mid position and be ready with the meter attached, no speakers, RECIEVER COLD no input and screwdriver in hand.. it will be out but not to a point that the amp is going to self destruct!

This is like a good crime novel, waiting for the clue, exelent job John

A Tom Clancy novel, this one!

I'm not out of the woods with this one yet. That's why I said I wasn't going to celebrate too much.

I tested it playing some music for a bit more last night and the receiver would randomly go into standby mode.  So something is unstable...and probably in the power supply I think.  Remember when I adjusted the 6.5v output I decided to adjust the trimmer to set the base of 16TR1 to 3.8V.  That resulted in the output being 7.02V instead of 6.5V.  The unit worked but later (and now) is unstable.

This morning I went in and decided to adjust the trimmer to back the output back to 6.5V.  When I plugged the Beomaster in, it went right into the original fault state with only "P" on the display.  Leaving it in that state I adjusted the trimmer to lower the 6.5V power supply output down from the 7.02V to 6.5V and the Beomaster clicked back into standby.  Unfortunately, it now randomly clicks back to the fault state.  So I believe I thave some unstable component in the path from the power supply module (16) through the motor control (06) and the microcomputer (02) ...still.

But that explains the original problem. When I first put the unit back together after the recap it would only go into the "P" mode. Had I known what I know how I would have looked at the 6.5V out of the power supply first.  Instead I took out the 02 board, spent a bunch of time messing with the timing circuit (when it was probably perfectly fine).  That also cost me the lamps for the volume control.  Eventually I found my way to the power supply and resoldered the components (also checking them).  That helped with the problem and I am now in the position where I am now - unstable power supply.  I will go ahead and replace the trimmers I guess.  The trimmer that adjusts the 6.5V output seems very steady though. As I said, when I checked the 6.5V output this morning it was still at the 7.02V where I left it. It also smoothly lowered the voltage as I turned the trimmer.

I also have the problem I observed where the frequency counter is unstable. I found out that those LS chips require a +5v power signal that is with 5%.  I also know from the earlier testing that those chips were not on and keeping the Beomaster in "P" mode when the power supply voltage was too high. It would be good to determine what the source of this instability is.

Some additional information now...(I think this is going to take a while)

I flipped the cover up and opened the back metal cover on the 02 microcomputer board.  I attached a test lead to the +5V that supplies voltage to the counter chips.  I turned the Beomaster on and it came up in "P" mode then clicked into standby mode.  I couldn't get a measurement at that point with my DVM (I'll have to use the scope later). While in standby mode I measure 5.12V at the test point which is good. I could put the Beomaster in the various operations - tuner, PH, TP1 and TP2.  All the while it measured the same on the DVM.  Then, it just clicked into the "P" fail mode.  I say click because I hear a click in the Beomaster when it does that.  The voltage on the test point stayed in range though - +5.02V.  I need to check the power supply for the processor next although in the past it was always at +5V.  Something is clicking on and off when the problem occurs though so I need to find that and whatever signal is toggling the unit.