Featured Post

Beogram Commander Remote Control: Maybe This is the Final Version!..;-)

This is a follow up to my recent post about the redesigned Beogram Commander remote control board, which now works in both (DC-motor) Beogr...

Saturday, August 2, 2014

Beomaster 8000: Restoration of the Output Amplifiers

As usual, I rebuilt and tested the output amplifiers (PCB #5) of the current Beomaster 8000 restoration project before turning it on the first time. While the ebay seller claimed it was 'fully working' there is always a chance that one of the output trimmers goes non-contact during transport, i.e. in my opinion it is worthwhile to do the outputs first and test them with external power supplies (see here for a description of the process: http://beolover.blogspot.com/2011/09/output-stages-testrecap.html).
This takes a bit longer, but definitely saves a lot of cost and effort compared to replacing the output transistors. Anyway, here are the before and after pictures...:

Left amplifier before: 


Right amplifier before:


It was definitely a good idea to replace the caps, most were cracked. Here is a picture of one of the 220uF caps:

I measured the capacitance and ESR of these caps, and they were still all in spec...pretty amazing, considering the cracks...it seems the capacitor situation depends a lot on how the individual Beomaster was stored/treated, and whether it was used regularly etc...

When testing the boards, the external power supplies showed the following currents after adjusting to 18 mV for both boards:

+54V--> 0.10A

This all made sense, so I reconnected the output rails and fired the Beomaster up. It came on with a healthy double relay click and then showed a nicely working display. It seems all segments are working - also pretty amazing, considering the 'white PCB' style of the displays. I guess it was really treated well in its pre-eBay life!
I easily tuned into my favorite local radio station and enjoyed a bit of their NPR programming. The only issue I could find during this brief first test was a not working 'filters' light...hopefully this is just a light bulb.

On to the power supply.

No comments:

Post a Comment

Comments and suggestions are welcome!