This is the frustrating bit. Some of the designs are spot on bar a few mistakes and cost cutting. Excuse the rant here but it annoyed me...
I feel your pain, and not only with regard to T&M equipment. There's so much crap software around, too. Drives me crazy with the "if they just..." thoughts.
Comparing the implementations between a £50 Mastech and a £627 Keysight/HP supply (yes thats full retail difference) ...
Mastech. Simple comparator using a left over LM324 and transistor to sample the output voltage and switch the relay on and off to select taps if it goes more than half of the power supply range. Blows up after 6 months.
HP. Simple comparator using a left over LM393 and a transistor to sample the output voltage and switch a couple of SCRs on and off to select taps if it goes more than half of the power supply range. Still works after 23 years.
Hang on a minute? That HP one is entirely solid state! Nothing mechanical to fail! How much does an SCR cost? sweet f-all! There's no patent on this idea, not that anyone cares in China. Price differential is at most half a dollar.
The BOM cost of the HP and the Mastech are actually about the same per channel. There's bugger all in either of them. Just some better quality pots and some marginally better quality components in the HP.
So close but so far
... and this is frustrating because I'd rather spent the price of a Mastech power supply than an HP one! In fact despite the explosion, the mastech one is easier to maintain. Also the comedy bit is the metering on the mastech is less crap.
It does make you wonder, doesn't it? In general, I think the deficiency is a form of cost cutting — no changes to the design means no time/money spent thinking, prototyping, etc. So, then why would some aspects be better on the cheap device? Perhaps someone else incurred the cost for that improvement and it just came along for the ride when the manufacturer received the files.
In other words, putting in that extra effort may simply be unnecessary in the current market. If their stuff sells as-is, it ain't broke and they ain't gonna fix it.
![Grin ;D](https://www.eevblog.com/forum/Smileys/default/xgrin.gif.pagespeed.ic.QVVz6XIT20.png)
Perhaps I should build an aftermarket "mastech power supply engine" which you can just rip the one out in it and stick a decent one in.
That would be interesting to explore. Of course, a big question is whether the numbers would work out. What would the cost of the better replacement engine (and the resources to do the swap) be compared to
tossingrecycling the dead supply and buying another el cheapo? Unfortunately, the market is quite adept at overlooking the long-term value for a cheap solution today.