It’s currently cold outside (-8 °C) here in Germany and I skipped my cycling tour yesterday. Instead I got myself some stuff to play with during the cold and dark winter days.
A “new” handheld oscilloscope Tektronix THS 720 (STD) appeared in my lab! It had a dead Ni-Cd battery so I replaced it with a new one. It seems to work, however, it also seems to have the usual aging issues with optocouplers. Channel 1 shows some DC offset while Channel 2 looks fine DC-wise. The price for this scope was really “OK” (<200 EUR), it’s great for troubleshooting switch-mode power supplies due to fully isolated oscilloscope input channels. It has a built-in multimeter to check voltages simultaneously – great tool for repairing broken test equipment! Well, this instrument also needs a repair, so it’s some kind of repairception? hmm
On the bottom right, we have four Sprague TANTAPAK® wet slug tantalum capacitors, 820 µF, 20-30 V(DC) each. If they haven’t been abused and aren’t leaky, maybe they will be used as decoupling capacitors for a nanovolt noise measurement of a LTZ1000ACH. Need to be tested for their capacitance, ESR values and leakage current. See Jim Williams’ work on Linear Technology Application Note 124. A HP 10514A mixer can be seen on bottom mid. Bought it out of curiosity, will test it. Top left shows a 10 MHz OCXO for a HP 53131A type of frequency counter. On the left hand side, a SUNSHINE IC socket fixture can be seen. A friend told me it was used along with an ancient SUNSHINE EPROM programmer PC card, the one with an 8-bit PC/XT-bus maybe?
Bottom left shows a Raspberry Pi 5 (8 GB) with a cooling fan. Raspi5 was announced in November 2023 but I couldn’t buy it in online shops because there were none available. It took them almost 6-7 weeks to restock their supply. I didn’t want to pay high prices for a Raspi 5 on second hand markets because the offers were 30-50% overpriced in the order of 130 – 150 EUR (which is crazy!). Will be a nice upgrade to my Raspi 3B standing army. I’ve ordered some accessories such as a cooling fan, the 27 Watt USB-C Power Supply, a black case, RTC battery, Micro HDMI adapter cables and a microSD card.
And there is a possible repair project on the horizon. A HP 3458A has presumably lost its calibration data due to a dead battery of the Dallas DS1220Y-150 Nonvolatile-SRAM. The NV-SRAMs in a HP 3458A store settings/preferences and calibration constants. As long as the unit is powered up, the battery coins inside of the Dallas ICs aren’t discharged. However, once the digital multimeter is turned off for a longer periods of time (e. g. months, years), the battery is slowly discharged. Unfortunately, the discharge curve of a NV-SRAM does not show any signs of discharge when measuring its voltage – instead the battery voltage drops suddenly below a power-up threshold and all stored data is lost. The life time of the battery can last between ~8 up to 30 years and it strongly depends on environmental and usage factors. Therefore: please do backup of your IC contents in order to prevent a potential nightmare.
HP 3458A is a famous example but there are also oscilloscopes out there (e. g. Tektronix 2465B/2467B, older TDS Series) with a memory-loss time bomb. I’m currently taking care of ordering replacement NV-SRAMs and will try to revive the unit.
I’ll resume my cycling efforts tonight. It’s no pleasure doing this at -8 °C mostly because of cold wind blowing into the face for about an hour or so. Nevertheless, there is no bad weather, only bad clothing!