HP5328A on the bench.
Seems to work fine, but the display comes up bright and then fades away within the next 60s or so. Popping the hood.
Some RIFA's on the 230V. Haven't released the magic smoke yet but I'm not going to wait for that. A few snips later:
Didn't solve the problem, wasn't expecting that either. Looking at the schematics, a 3.5V rail is feeding the display:
![Test Equipment Anonymous (TEA) group therapy thread](https://www.eevblog.com/forum/index.php?action=dlattach;topic=81471.0;attach=2320701;image)
Probing around shows the voltage decaying over time. Digging up the 3.5V supply schematics:
![Test Equipment Anonymous (TEA) group therapy thread](https://www.eevblog.com/forum/index.php?action=dlattach;topic=81471.0;attach=2320705;image)
Poking around some more and I notice the 75 Ohm current limiting resistor measures
way low. Just to make sure, I take it out of circuit. Still low. About 0.75 Ohm or so.
Uh...
Yeah, the dot was missing as confirmed by the color code. Also makes sense, a low value current sense resistor would rather result in voltage high than voltage low.
And this, kids, is why you should write 0R75 or something rather than .75.
Putting back the resistor, I noticed that the voltage over it remains stable during the decay. As it starts out at 3.5V, it's fair to say the converter works and is working in current limiting mode. So the problem should be in the display module itself... I actually have a spare but I figured let's have some FLIR fun first! Nothing weird on the display but... Hangon, who that? Only 70C or so but you wouldn't expect much more with current limited at 0.5A or so and only 3.5V.
![Test Equipment Anonymous (TEA) group therapy thread](https://www.eevblog.com/forum/index.php?action=dlattach;topic=81471.0;attach=2320709;image)
A 22u cap, not on the schematic. *snip*, *snip* and io and behold!
![Test Equipment Anonymous (TEA) group therapy thread](https://www.eevblog.com/forum/index.php?action=dlattach;topic=81471.0;attach=2320713;image)
Actually a rather nice specimen. Ovenized oscillator (soaked for a few decades for your pleasure), the 512MHz option, GPIB. Me happy.