Ebay horror ...

> > > minutes it takes to swap them, and it costs 100x that much to fix the

> > > board, at a minimum, it seems to make sense to swap the board. That

> fix > > > > Are you seriously telling me it takes you 1000 minutes (or over 16 hours) > > to fix a serial board? The only time it could take me that long is if the > > 'serial board' was something like a DEC DMR11, and it had a nasty logic > > fault in the microcoded processor. > > > I'd never spend more than that 10 minutes I mentioned before on a serial

Nor would I spend any longer than that, because it wouldn't take me any longer than that... > board, because they only cost 50 cents or a dollar at the thrift store. If

You also have to consider the time taken to go to the thrift store, buy the item, and come home. In my case here that would be around 1 hour, I think. Hmm.... > have a complicated serial board, i.e. one that doesn't talk the "normal" > asynchronous protocol, and that runs at a higher rate, e.g. 4.762 Gbps, and

The DMR11 is not particularly fast (in fact it's slow by modern standards), but it does have a 'processor' on it (a lot of TTL parts and microcode PROMs). It's not the sort of thing you can replace with bits from the local PC shop, charity shops, etc. Oh, and it's a Unibus card for a PDP11 [Before the DEC enthusiasts here leap on me, yes I know it's physically 2 PCBs. I have enough of them, the printset, etc.] [...] Isn't that the truth :-( [...] > > > True, but not if you don't fiddle with the cables. Moreover, even the

> > > > Actually, a serial port meeting RS232 standards should be able to

> > hot-swapping of the cables. Shorting any 2 pins together, or to ground

Because half of them don't actually meet RS232 standards!. And dodgy grounding doesn't help. If the peripheral (or whatever) is not properly grounded, the 0V line can be floating at half mains voltage wrt local ground (due to the capacitors in the mains filter). That can zap the RS232 buffer chips. Because sockets cost money, and most users wouldn't know how to replace chips anyway... I have seen devices where the I/O buffer chips are socketed (and almost nothing else is), presumably to make them easy to replace, though. > > Over here 'charity shops' (==thrift stores) don't generally sell > > computer parts. They may sell complete computers if you are lucky (and > > can find a volunteer to do electrical safety tests). But I've never seen > > a serial card or anything like it in one. > > > The common PC at a thrift shop has had the "interesting" boards removed,

As I said, this is a country-specific thing. Over here, mains-operated electrical stuff has to be safety tested by a 'qualified person' before it can be sold. Since most charity shops are run by volunteers who have no knowledge of electrical stuff, most such shops can't sell second-hand computers, etc. And they certainly have no clue as to what 'interesting' boards are. I doubt they'd ever consider opening up the case. > PSU and fan costs $22. At the thrift store, you get a used fan with the

> but it will get you through a few days until you can order and take delivery

TO be honest I'd rather by a _good quality_ fan from somewhere like RS components and install it in the original PSU. It'll cost more, but I won't be fixing the machine again in a year's time... > > I have to conclude that either you're soldering with an arc-welder or you > > are taking months to change a single chip. > > > It's not months, but electricity isn't that cheap here. My soldering iron

I am still very suprised. Soldering irons are not exactly high-power devices... > butane, by the way, but still, it's much cheaper to replace the entire

I must get a butane soldering iron sometime -- for 'field' repairs. When I'm at the workbench I prefer a temperature-controlled soldering iron. Period. > > For 'static' equipment (i.e. not stuff that's carried about, mounted in > > vehicles, etc), turned pin sockets (machined pin sockets) seem to be > > reliable. I always use them on my prototype boards, not because it makes > > it easier to replace chips, rather that it's easier for me to pull chips > > and force signals high or low when tracing design bugs. > > > Yes, but they cost like the devil, and the pins on the wire-wrap types are

Sure, but they are relaible. I don't like wasting time tracing faults caused by poor-quality components. And if I'm demonstrating a prototype I've designed, I want it to work reliably. Having had a few problems from folded-contact sockets, I went over to turned pin ones exclusively. And never had any more problems... You can always cut them dowu... > > Once I've got the design worked out, I socket (unless there are good > > reasons not to) : > > > The sockets take up considerable space perhaps better used for air flow.

If it's one of my own devices, I'll just use a slightly larger box and keep the airflow that way. If it's going in a cardcage, then yes, I might need to not use sokects to keep the airflow right. -tony