The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)

[modeng200023]

Andrew, you just amaze me

John

[Muzzerboy]

Yes, the hot air ones are the way to go and don't cost a lot. The irons with the funny tips end up ripping pads off if you aren't careful and you never seem to have the right tip anyway....

[awemawson]

Andrew, you just amaze me

John

Thanks John 

Some more progress. I've linked out the faulty transistor from Collector to Emitter to allow me to carry on testing. This transistor is involved in the switching to / from battery back up so in this mode I can do without it!

This has let me prove that A12 inhibits all Chip selects when low, and the other four control lines (B13, B14, C13, C14 ) provide Chip Select for each individual Ram chip.

All a bit odd, but workable.

The picture of the link across the SMD transistor emphasise how small SMDs are - that huge hoop of billet is actually the lead from a tiny 1/8 watt resistor 

[PekkaNF]

....
The bread board having arrived has let me think a bit more about the physical side of further testing, or rather  oscilloscope probing of the board under test. As most components are SMD's, unlike through hole devices you need to be able to probe both sides of the PCB. This dictates that either I stand the board vertically (which makes getting at it a pain) or have the board connector hanging off one end of the breadboard.

I've chosen the later method but this has persuaded me to incorporate header pins to connect to the Arduino rather than as I had previously intended - using directly soldered flying leads. My drawer of rows of header pins is a bit on the low side so an order has been placed with RS.

I have bought this kit:
https://sensepeek.com/pcbite-kit-with-2x-sp200-200-mhz-handsfree-oscilloscope-probes

pros:
1: It has pretty much standard 10x scope probes and they work per spesification, the business end is small and has a standard needle pogo pin.
2: probes are held down with a weight and the swan neck tube holds them in place, it works
3: The magnetic standoffs works too.

cons:
Ground hook is not that great, but it has standard square pin connector and easily replaced.

I though of making something like that myself and played around of different parts etc. and never got really good results. I tried those cheap colorful flexible coolant hose thingys, but they really are not very precise or dependable in real use.

This commercial product does what I needed better that what I could have cooked. However it is just one part and I still solder wires and connectors on boards, just getting better at it.

There is a 1:1 flying lead probe too for non coaxial cables, but those I haven't tried.

Pekka

[awemawson]

That's a very cunning system. The magnetic pillars are on my 'to do' list for making and although that probing system looks pretty good it won't let me probe both sides of a board at once.

I fear I'm stuck tagging on wires with solder at times !

[PekkaNF]

Jep. No system works for all ocasions and I often run out of hands, those two extras help.
https://www.bot-thoughts.com/2013/01/easy-pogo-pin-test-jigs.html
https://blog.adafruit.com/2013/07/08/using-pogo-pins-to-shrink-6-pin-isp-connectors/

There are some easy solutions for batch of boards, but to test economically single board on hobby setting needs soldering - eventually.

[awemawson]

My 'Hot Air Re-work Station' arrived by post today. I have to say that I am impressed with what you get for your money. (£36.67 plus post - total £44) and it seems quite well made. My photo doesn't show it but a temperature controlled soldering iron is included in the kit that plugs into the base unit.

A bit busy today but I had to try it out. I removed a resistor pack from the original RAM card that got dissolved, and it seems that the pack is in good enough condition to re-fit if needed, so a good result for a first effort.

I need to research what temperatures to use - the solder melts below 200 deg C but most on line sources say use 250 which is what I did. But what temperature can IC's stand and still survive?

[awemawson]

I got a  bit more time this afternoon, so decided to remove at least one of the suspect 74HC00D SMD chips to find why A12 wasn't floating 'high' as expected.

So - first chip out and I powered up and A12 is still 'misbehaving' - so then I took the second chip out as A12 connects to two gate inputs on both chips. Argh - A12 STILL misbehaving 

OK what's going on here  Well it turns out that the termination of these five control lines is not a simple 10k pull up to 5 volts,  but also a 10 k pull down to 0 volts.

All five control lines pull up to 5 logic high and down to logic low with a 1K5 resistor so it's all been a none problem - how very familiar !

OK something else learnt, AND practice using the SMD hot air gizmo. I decided to re-install the two chips and darn me they have survived the exercise and still work!

But I MUST sort out physical connections to this board - pushing female jumper leads onto the edge connector is very unsatisfactory - I must knuckle down and solder up the bread board that I now have.

Still - happy that I can not only remove SMD chips but also put them back and they still work 

[awemawson]

So why haven'i I done the breadboard yet?

Well I've been waiting for inspiration to get over a little 'problem-ette' - the bread board designer certainly laid it out to take a DIN41612 three row 48 pin socket, but only the outer 'A & C' rows of pins are brought out to the body of the board - row 'B', the centre one, is all on it's ownsome lonesome and will need jumpers, which cannot be on the component side if the socket is to sit correctly.

OK it's only 16 links - 32 soldered joints - but I've been trying to work out ways round it ! Years back I'd do links like this in 'self fluxing' enamelled copper 'magnet wire' where a good hot soldering iron would volatilise the insulation, but I'm not sure if I have any left - time to go hunting in the wire stash 

The plan is to have the Arduino fixed to the breadboard as you may well have gathered from the picture.

 . . . I'm off wire hunting . . .

[awemawson]

Well it seems that I have

Buried in a dusty box I found two rolls of self fluxing wire - one rather too thin and the other rather too thick - oh well 'it'll do'

Iron needed cranking up to 475 degrees C to effectively remove the enamel, but it DOES work !

More experimentation later I think

[Muzzerboy]

I assume you are using leaded solder? That melts at a lower temperature but either way, the reflow temperature profile is often given in datasheets these days. The actual reflow part of the process is typically around 230-250C for 45-90 seconds or so for lead free solder. Pretty much everything made these days is SMT, so all compts are designed to tolerate those temps without degrading.

[awemawson]

As expected, soldering jumpers to the centre row (B) of the DIN4161 connector was a nightmare. Poking a soldering iron down between the pins inevitably scorched the  insulation of previously soldered wires. I thought perhaps I could use PTFE insulated wire - I have some the right size, but frankly I've never been able to satisfactorily strip the insulation neatly and to correct length - it always ends up a mess.

Then I thought, if I can find a crimp version of the connector, I can put it on pigtails off the board and solve the issue. Sure enough, Harting part number 09230483217 is the right part - but it's on a ten week lead time from all the normal UK suppliers so that rules that out!

OK the socket that I have has solder tails intended for a PCB, BUT 16 way female socket headers fit them rather nicely - three of those and I have a hopefully working solution. Solder the three headers individually thus making the 'middle row' a none issue, push them on the back of the socket and hang the socket off the board on a short umbilical cable This also makes inverting the board for test far easier.

But as the female jumper leads that I've been using with the Arduino were themselves rather unreliable - falling off at a mere touch, a better breadboard solution was also called for. I've found one with screw terminals AND header sockets so this may be the best of both worlds.

. . . . we'll see when it arrives !

[awemawson]

The new breadboard with screwed terminals arrived today. Very confusing when you buy from eBay and an item is delivered by Amazon in Amazon packing !

I must say that I'm impressed by the build quality and it looks like it will meet my needs. I'm now waiting for a delivery from RS of '0.7 mm Boot Lace Ferrules' that will plug into the existing female push fit sockets AND go in the screw terminals (keeping my options open). I do have 1 mm boot lace ferrules but although they fit the screw terminals they are no good for the push fit ones./

. . . . getting there slowly - one tiny step at a time 

[awemawson]

Things have been a little slow on this project - RS Components let me down on the bootlace ferrules that I'd ordered. Unusually for them they arrived a few days late and when they came they were not the same spec as described in the catalogue. I needed ones with an O/D of between 0.65 and 0.8 mm. There were two types catalogued with O/D 's of  0.7 and 0.75 respectively so I had ordered some of each. When they arrived they were 1.05 and 1.1 O/D. I/D had been specified by cable size and they had entered the I/D as the O/D in mm. They were gracious enough to acknowledge their error and the engineer even went to the trouble to confirm that it was only this size were mis-described. No big deal but it's cost me a few days when I could be getting on with things !

So I've reverted to 'Dupont' pins - which I don't particularly like as they are a bit fragile, but needs must, and of course this incurred a further few days of delivery delay.

OK we are where we are ! So today the coloured heat shrink arrived allowing me to code up the 48 wires. There are three banks of 16 wires, cabled in correctly colour coded wire, but being 1 to 16 each bank has two 1's 2's .... 6's. So each bank needs a sleeve to indicate which it is (A=Yellow, B=Red, C=Blue) and in each case wires 11 to 16 have a white sleeve to differentiate them from 1-6. This may seem pedantic, but believe me without this detail things rapidly get very confusing when fault finding !

So this morning I have done the wires and crimps of 'Bank A' and I'll give my eyes a rest until a bit later to stop me going cross eyed !

Meanwhile the programming of the test program has been progressing but isn't yet finished.

[djc]

As a general observation on life, I have never understood why, when we have three things to distinguish between, we use three labels. Two labels and 'unlabelled' is sufficient.

Everyone wants to start counting at 'one', seemingly forgetting that 'zero' can be used.

When you see videos of people dismantling things (e.g. a chair), they label the legs 1, 2, 3, 4 when 1, 2, 3 and no label would do. How much masking tape is this costing the planet?

I wonder if there is any connection with a person's favourite computer language - whether arrays are zero-indexed or not?

[awemawson]

Well in this project, pre-determined is that the data lines are labelled 1-16 but the address lines are labelled 0-15, and even worse, the data line appear on pins with A(nn) numbering leading to all sorts of confusion.

However, personally I think things should be labelled as what they are! If labelling a class of four items as 1-3 and no label, you are stuck when label 2 falls off, and in the real world this happens all to often.

[awemawson]

So I got the remaining rows 'B' & 'C' crimped and sleeved so now at last perhaps I can get down to proper testing!

[WeldingRod]

That's easy!  You label all four because that way you have a check sum ;-)
Otherwise, if your tape fails you have two identically "not labelled" parts...

Sent from my SM-G892A using Tapatalk

[vintageandclassicrepairs]

Hi Andrew
I have to admire your enthusiasm and energy pursuing  this fault finding "adventure"
In a previous life I worked as a spark and instrument tech at a combined cycle gas fired powered station
Seeing the multitude of connections on your "test rig" reminds me of  my work back then
All long gone now (including me)!!

John

[awemawson]

Thanks for your kind words John.

I don’t HAVE to do this but it keeps my brain working!