Beomaster 6000 (2253) start-up problem

I’m stuck and could use some help, Beomaster 6000 won’t start up. Some LED segments light when connected to mains power but nothing more. No relay action, nothing. Everything I test looks normal now. It seems like it won’t reset and go into standby.

Background: I rebuilt the amp and pre-amp years ago, sent it off with a friend who has used it nearly daily for about 4 years. No problems, until it would start for him.

What I know: I have a known working Beomaster 6000 that I removed the front panel, (boards 2,3,4,5) and connected to the faulty Beomaster. Works fine. So I can eliminate any problems up stream. Problem follows with board 2 when swapped.

5v to board 2 is intact. Unable to calibrate the reset according to the manual, R89 pot was bad, replaced it, then I was able to calibrate appropriately with the scope. The 2 original electrolytic caps on board 2 tested as good, replaced with new.

4.9V on processor pin 39.

Swapped processor with the known good processor from the working Beomaster. No change and the processor from the faulty Beomaster works in the good Beomaster so I can eliminate the processor. Tested D6, TR 5,6, 27, 28. All voltages as excepted and test as working out of the unit according to my PEAK component tester. Shorted R90 to manually reset several times. Reflowed solder on all connections a couple times. Replaced 40pin processor socket.

Nothing.

I grabbed a parts unit Beomaster 6000, that too has the same problem of not going into standby, tested and shows a good processor. Haven’t spent much time with that unit.

So, I have 2 Beomaster 6000s with the same problem on board 2 and a known good Beomaster to compare to.

Every voltage point I see on the service manual I test as appropriate so I can’t pin point where the fault is and could use any help thinking this through.

Hi

Regarding to the servicemaual Page 6-6 maybe you try to look for the "TIMEBASE" of IC 4 PIN 15. Should be 664 Hz.

On TR 10 I think you can't measure anything because the Probe of an oszilloscpe will draw down the Cristal frequency.

A good place to start would be Collector of TR 11.

The Timebase is generated from the Crystal X1 goes via TR10 and TR 11 to IC 6 PIN 1.

Comes out as a divided signal on IC 6 PIN 6 = 15,5 kHz.

Goes to IC9 PIN 14 comes out divided on IC 9 PIN 12 = 7,75 kHz

Goes to IC 7 PIN 14 comes out divided on IC 7 PIN 11 = 664 Hz

Goes to IC 4 PIN 15 "TIMEBASE"

I'm not completely sure but I think this Timebase is used to get the buttons working with a strobe signal.

Without this you won't be able to swich on or off or anything else.

 

Let us know if you got any progress!

Kind regards

Christian