Beomaster 8000: Ready for Some Bench Testing

Ever since I restored the power supplies, output amplifiers and preamplifiers on this Beomaster I have been exercising it with an iPod through TP1 & TP2 as well as playing the FM radio. The receiver has continued to play and sound very good as I added the restored FM boards, Filter & Tone Control board and the Microcomputer board. Now it is time to start putting the Beomaster back together and do some bench testing.

As I started the reassembly I tried the remote control for the first time. No functionality. So I will have to dive back in to the power supply board where the remote control receiver lives to see what is wrong. But first I decided to continue with some initial bench testing. I have been anxious to take some measurements and I don't see any reason to let the remote control problems delay that right now.

Before using any test equipment I decided to run a functional check pairing the Beocord 9000 that I restored earlier. These two will be returning together to their owner soon and I wanted to see how they play together for the first time since their restoration.

I used an original seven pin DIN cable for TP1 to connect it to the Beomaster. Pressing the play button on the Beocord turns puts the Beomaster into TP1 play mode as expected. Pressing the standby (off) button on the Beomaster turns both units off (and into standby mode). So they are communicating well. The Beocord also sounds great. In a later bench test I will add one of my Beogram 8002 turntables to the mix so I can both check out the phono input and do some recording on the Beocord.

Next up for this testing session though is to use my QA400 spectrum analyzer to check the Beomaster 8000 from its source input (TP1) to its output amplifiers (Speaker 1).

Beolover has featured some measurements before from his QA400. It is a nice little bench analyzer that uses a PC to do all of its analysis. The connection to the computer is via a USB cable and software on the PC sets up the tests performed. Up until now I have only done low voltage level testing with this type of setup because the inputs to sound card devices and this QA400 are limited to the ±5 volt range. Connecting to the power amplifier outputs was not doable. I picked up some differential voltage probes by the QA400 manufacturer that will allow me to measure higher voltages. For this Beomaster source-to-speaker test I will use a couple of fixed 8 ohm loads to simulate speakers and connect the differential probes to the dummy speaker connectors.

The probe is powered by batteries and has a BNC connector to run a coax cable to the QA400 input terminal. For some reason I could not get my test setup working as I wanted with both differential probes connected at the same time (one for the right channel and one for the left channel). With both probes connected I see some undesirable noise at 60 Hz from my house line voltage. So far swapping cables and probes doesn't solve the problem. The only thing that works is using one of the probes on one channel at a time. Then there isn't any 60 Hz noise present. So I performed my tests one channel at a time switching the speaker connection to the Beomaster. The measurement results look pretty good. I won't post all of the frequencies I checked (400Hz, 1kHz, 5kHz, 10kHz, 15kHz) but here is the 1kHz test on the left channel. I tested with the analyzer set to unweighted and A-weighted.

Here is a 5kHz test on the right channel.

Viewing the distortion numbers and sound to noise level readings at a few select frequencies was nice to see. This Beomaster sounds really good but I like to see some sort of measurable result besides my own ears.

Now it is back inside to see what is wrong with the remote control receiver.