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Beolover SyncDrive: DC Platter Motor Replacement for Beogram 4002 and 4004 (Type 551x and 552x)

Late Beogram 4002 and the 4004 (Types 551x and 552x), which have DC platter motors instead of the earlier synchronous AC motors usually suff...

Monday, May 18, 2015

Beomaster 8000: Inputs Not Working

A Beomaster 8000 that I rebuilt last year arrived a few days ago for trouble shooting. The owner told me that he suddenly lost all the inputs. No matter what input button was pressed nothing was audible, while the display would show the right input etc...This indicated to me that the uProcessor was working properly. So I opened it up with the plan to look into the chain of command between the uProcessor and the input selector chips. Since both channels of any input did not work, I hoped I could rule out a failure of the input selector chips. 
Once I had the unit open, I turned it on. Everything worked. That is of course frustrating if the problem is intermittent. I started methodically wiggling the connections between the uProcessor and the input chips. Nothing came up, everything was stable. 
Upon further reflection (while listening to some nice NPR jazz on the frustratingly working Beomaster) I determined that an interruption of the power supply of the preamp board would have a similar effect. So I checked the connections between the power supply board and the preamp. And indeed, when wiggling P46 that carries the power rails to the preamp board, I was able to get the inputs to turn off occasionally. So there was a bad contact somewhere. Here is a picture of the area:

The colorfully wired vertical plug is the one in question. This area is also prone to cracked traces on the circuit board due to the multitude of connectors that torque the board in that corner. A bit of a design weakness.
I took the board out and inspected for cracks and the like, but was not able to find anything obvious. So I resoldered all the headers and cleaned them and put the board back in hoping that a hairline crack in one of the header pin solder points was the root cause. After reconnecting all plugs, I fired the Beomaster up and wiggled the plugs in that area again, and nothing happened anymore. Seems everything is stable now. So it seems this issue may be fixed...but of course with intermittent stuff, one never really knows until one knows.

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