BM6000 won't go into standby.

6 replies
RI
Offline
richtoy
Bronze
Posted August 9, 2014 at 22:53 GMT
#2200543

I have a BM6000 that I put down a couple of years ago because I suspected the CPU was broken but after browsing the old workshop forum today I decided to have another look.

The machine has been fully recapped and when power is applied one of the volume arrows lights up and there is a single zero in the display.

The 6.5 volts looks good and the processor reset looks like it is working but what I don't see is the 50Hz into CPU pin 16 from the PSU.  Should board 16 (the PSU) really output a 5v square wave as indicated in the circuit diagram?  I have changed 16TR4 twice but it makes no difference.  There is a reasonable square wave on the base and it is biased at 0.4v.  Does anybody remember if they have seen a nice 5v 50hz square wave on P42-1 and is the square wave still present if the plug is removed?  I am assuming the CPU is acting as the load on the collector of 16TR4.

Thanks

Richard

Location: Netherlands

S(
Offline
sonavor (archived2)
Bronze
Posted August 10, 2014 at 16:08 GMT
#2200544

The Beomaster 6000 and 8000 can behave strangely for a lot of reasons. You said that you read some old Beoworld threads on the BM6000 and have recapped the unit so it sounds like you have already done a lot of the things I would do. Examining the CPU can yield good information but often the little problems are due to connections (solder joints on connectors for example). 

I'm not currently at the point where I can take some measurements to compare to yours. I do have a couple of BM6000 units I need to work on but I won't be able to get to them for at least a month. 

RI
Offline
richtoy
Bronze
Posted August 10, 2014 at 21:24 GMT
#2200545

One extra bit of info, if the PSU caps are allowed to discharge before power is applied then there is a brief "P" displayed before the volume arrow and the zero.  However, I am not sure if that is a good or a bad thing...

Richard

Location: Netherlands

S(
Offline
sonavor (archived2)
Bronze
Posted August 11, 2014 at 06:35 GMT
#2200546

Have you checked all of the voltage supply values in module 16 (Power Supply)?

RI
Offline
richtoy
Bronze
Posted August 11, 2014 at 21:41 GMT
#2200547

Yes, both the 6.5 & 15 are good.  Furthermore, both the clock and the Time base on pins 1 & 15 of the CPU are present and correct.

The only thing missing is the 50/60Hz on pin 16 from 16TR4 but as I said above, I don't see how bit of circuit works.  

Location: Netherlands

RI
Offline
richtoy
Bronze
Posted August 12, 2014 at 08:28 GMT
#2200548

Pin 16 of the CPU is an I/O port and the Fairchild F8 datasheet indicates that this would normally be driven from TTL with an open collector.  I made a simulation of the circuit and all starts working correctly as soon as a load is applied to the collector of 16TR4.  There is continuity between the collector of 16TR4 and pin 16 of the CPU so my conclusion is that the pin is open circuit inside the chip 🙁  I will try adding a 10k load resistor between pin 16 and 5v tonight to see if it makes any difference...

Richard

Location: Netherlands

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