HP 8569A Spectrum Analyzer: two mysterious resistors

Again, some repairs of a 8569A spectrum analyzer. This time, no problem at all with the front selectors and contacts that break all too often, but with the CRT showing only a defocused vertical line. Some probing around – the analyzer appears to be find but something wrong with the deflection circuit? This is on the A5 assembly, and with no extender board around, quite difficult to probe, and a bit dangerous because this assembly is using +120 VDC. Any short may damage the supply, and any touch may give you a shock. So better exercise some care. By soldering wires, I was able to trace the signal and it seemed to be OK up until to some of the last amplification stages of the X amplifier. Maybe something wrong with the transistors – no these are good. Probing around on the board, checking all values of components close-by: the 75k resistors (fairly large sized 0.5 Watt resistors) are high-resistance, both seemed to have failed at the same time – strange. Eventually, this is becoming a quite frequent failure, already the 5th case or so over the last few years of open high-ohmic, say, 100k and about, resistors that are subject to 100 V or similar “high voltage” usage.

With no suitable 75k resistors available, I went with a combination of 82k parallel to 880k, resulting in 75.01k, close enough. And the 82k resistors that need to carry most of the current are really good old low inductance transistors suitable for such 100 volts service.

The repair, it is not particularly beautiful, but it works and at no cost, with available parts. Finally, some hours of test to make sure there is nothing else at fault in this unit. All good, test passed.

Heating energy consumption: first evaluations, and total annual energy demand

In the meantime, I have collected enough consumption data for gas consumption (mostly heating, some little bits for hot water), and at various temperatures outdoors, including, very cold temperatures.

As it turns out, the gas consumption correlates well with the outside temperature (daily average temperature in 2 m height, as officially recorded close to my place by the weather authorities).

With datasets of daily temperatures for 2019 and 2020, we can then estimate the total gas consumption of these years.

The 2019 predicted consumption:

The 2020 predicted consumption:

For German standards, everything less than 100 kWh per m2 and year is quite reasonable. I need to admit that not all of the rooms are fully heated all the time, but well, it is not all that bad, comfortable, and affordable.

Here an energy rating chart – in German – around 100 is a good value, above 200 … there it is getting really bad, wasteful and expensive!