Last week I assembled my first transistor tester (bought the kit on Amazon). It appears to be working but there are a few strange things going on. Maybe you can help me in troubleshooting it? It's the kit in a red PCB board with
k1036038s
2578AY-AT
It's the same layout as shown in the attached picture (taken from the net, probably this very forum).
It came with firmware version 1.12k and a spare 7550 (for which I was unable to find a datasheet) and I have already done the calibration procedure twice - from the menu.
Here are the oddities, in no particular order:
0 - After hours of non use, battery voltage is reported lower than what it actually is: at startup it says "Battery 8.9V while the actual battery with no load is 9.2 V (IIRC). This could be just a loading effect, but it is worth mentioning it. See also point 4
1 - When I repeat the measure of a resistance I get increasingly lower values. A 12.5k resistor is given as 12100 ohm the first time, 11980 ohm the second time, 11648, 11245, 10956, 10437, ... (I am making up the values right now, but that's the trend - with the resistor untouched and only subsequent pressing of the knob I went down under 9k with no fixed point in sight). And this is bad.
2 - The same is going on for caps, but I could attribute that to the fact the the measuring procedure is charging them a bit 9316 pF, 9281pF, 8953pF, 8619pF, 8307pF,... and these are actual values just measured with the time between them due to typing the numbers in this post.
3 - The spare 7550 is not identified. Is this normal for this firmware version?
4 - I just noticed that battery value too is getting lower at each pushing of the knob, only to come back to 8.9V if I leave it off for a long time.
What do you think?
there mus be a cap somewhere that is not discharging?