Beomaster 8000: Updating the Displays - Preparation

The next task on the list is updating the Beomaster 8000 displays. For the big, segment displays that means replacing the original Beomaster LEDs with modern, surface mount type LEDs. It would be great to be able to leave the original LEDs  (and sometimes an owner will do that), but eventually those LEDs fail. These units are thirty-five years old now. It is expensive to ship a Beomaster 8000 due to its size and weight plus it is a good idea to keep shipments (as in re-shipment) to a minimum. Lessen the chance of something bad happening in transit.

Here are the segment displays from some Beomaster 8000 units.

The first step is to get a test rig set up for these Beomaster displays. The work will be just like I did earlier on the Beocord 9000 display (...just more LEDs). You can setup a jig without load resistors and use the current limiting of the bench power supply but I want to set up my jig with individual control lines and load resistors like the Beomaster. I came close on this initial test set up but ran short of 68Ω and 82Ω resistors. I will have to add them to my next Mouser order which will probably be this week. Anyway, though not completely like I wanted, this test rig will allow me to check the reworked display boards. This picture shows the rig with a set of Beomaster 8000 displays that have all working LEDs.

Here are the individual Beomaster 8000 display pin mappings.

Now I am off replacing the LEDs with new SMD LEDs. Once that is complete I will use the test jig to run the displays for a few hours so I will know they are good. Then they will be assembled and re-installed in the display board. While the LED burn-in test is running I will be able to do the recapping of the display board and the microcomputer board.

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: 

after:

Right amplifier before:

after:

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

-54V-->0.11A

+15V-->0.01A

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.

Beomaster 8000: First Look Inside

It seems the last Beomaster 8000 is now happy, and I put it back together. It went to the living room for a few weeks of testing amongst his friends the Beogram 8000 and the Beocord 9000.
Time to open up the next 8000 in line! This one is very nice on the outside, and the interior is not different. While it was opened up before (slight screwdriver mark on the glass cover - still have to see an 8000 without...it is definitely a good idea to protect this corner with some tape before opening them up...). There is also an about 15 year old cap in there (6C35 to control the 5V ripple after the voltage regulator). But whoever did it put it back together properly...all screws the right sizes, nothing missing, even the small copper damper for the control panel door release is in its proper place.

Otherwise, it is as original as it gets upon visual inspection. Also very clean. Almost no dust! Very nice! Check out this left channel output board: Almost as it were recently put in a cleaning bath:

But, appropriate for the age, two of the red electrolytic caps are cracked, indicating that a full recap is probably a good idea. The output resistors are non-browned, which makes me hopeful that it really still worked as it was advertised on ebay.

The displays are unfortunately pre-solder mask style, as is evident from the whitish epoxy boards:

We will see how the segments are when I turn it on the first time. Experience tells me that this style displays is prone to segment failure. It seems that displays with the greenish epoxy boards may be more stable over time.

Next step: As usual, I will rebuild and test the output stages before the first turn on.