Recent Posts

Pages: 1 ... 8 9 [10]
91
New from Old / Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Last post by awemawson on August 30, 2021, 06:28:10 AM »
So with a flurry of activity this morning I think I've got all the components accounted for and correctly interconnected on the circuit diagram - phew that was quite a bit of labour and eyestrain!

Of the 48 pins on the edge connector only two are not used (C15 & C16)

I still don't know what the SMD chips 'AJ' actually do, but from the circuit you can see that they are turning on the PNP transistor 'SMD-DB' when 5 volts is coming in from the edge connector, and turning it off when it's not present allowing power to pass to the RAM chips normally from the incoming supply, and be powered via the diode '45-SMD' from the lithium battery when system power of 5 volts goes away.

By my calculations the 'Low Battery Alarm'  (Pin A16) should be asserted when the volts of the 3.7 volt nominal battery fall to 2.8 volts.

Now I have the circuit I need to work out how to actually test it and hopefully fix what is wrong. The battery side should be pretty simple. Power up the card with 5 volts, replace the battery with a variable lab supply and see what happens when the voltage is lowered from 3.7.

However testing the rest isn't quite as simple. Simplistically all 16 address lines and 16 bi-directional data lines should be able to be toggled by applying a TTL signal so any 'stuck bits' could be found, but Id like to build a proper tester that writes to the ram and checks what is written. My first thought was something like an Arduino, counting up the address line in binary, and performing a write and a read but the number of input output pins gets large.
16 address, 16 data, plus Chip Select, Write Enable and Output Enable is 35 I/O lines - will an Arduino do this - I have no idea never having used one! I can cut the number down by 15 to 20 by building a 16 bit counter circuit for the address lines and just incrementing it but that limits me to only testing addresses sequentially which is not ideal.

. . .so comments please from all those Arduino experts out there !

92
Introductions / Re: hello from dominican republic
« Last post by krv3000 on August 29, 2021, 07:16:12 PM »
hi and Welcome
93
Tools / Re: tool tip No 2
« Last post by tom osselton on August 29, 2021, 06:09:19 PM »
There is this in the resources area.
https://www.gewinde-normen.de/en/index.html
94
Tools / Re: tip of the day
« Last post by RussellT on August 29, 2021, 05:18:02 PM »
Another forum im on had a guy selling an angle grinder because "he didnt need 3"....

The shouts suggesting 4 or 5 to be the absolute minimum saw him withdrawing it from sale.

Yes, agree 100%.  I have 4 and I still have to change discs.

Russell
95
Introductions / Re: hello from dominican republic
« Last post by shipto on August 29, 2021, 04:38:47 PM »
Welcome  :clap:
96
New from Old / Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Last post by jiihoo on August 29, 2021, 01:37:04 PM »
Watching with interest and learning from your reverse engineering techniques.

Tying all inputs of CMOS chips to a high or low level should be standard practice. Most CMOS chips (logic gates and comparators) will start oscillating if they have floating inputs, which can cause excessive current consumption and may interfere with adjacent circuitry. I assume Andrew knows this; this explanation is for others reading this thread :D
97
Project Logs / Re: Building a box tool
« Last post by shipto on August 29, 2021, 11:57:10 AM »
The cutting part seems to be working ok its a bit rough because the stock was 6mm rather than 1/4" but hopefully when I use the proper sized stock it will look better.

Now just need to sort the handle out for the parting off bit.
98
New from Old / Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Last post by awemawson on August 29, 2021, 11:30:56 AM »
Another day going cross-eyed but quite a bit of progress  :thumbup:

I initially concentrated on the 'low battery alarm' circuitry which uses a dual precision comparator chip. Got it's wiring worked out but I couldn't for the life of me find where the output of the second part went. I couldn't trace ANY pcb tracks but it's not easy with SMDs ! Bright torches help shining from the other side, but not in this case. In the end I decided to butcher the original battery RAM card that was dissolved by the lithium juice prior to my ownership, and take the 8 pin SMD off the board. Hot air gun suitably applied only to reveal that despite the fact that it's inputs are connected, IT'S NOT USED  :clap:

OK go back to chasing real bits not virtual ones. Next on my list to nail was the three pin SMD labelled '45'. The look up list for SMD's said it could be a pair of diodes, a single diode, a transistor, or a voltage regulator so not much help. In the event looking at the original card (where this chip had completely disappeared!) in fact only two pins had tracks attached so it could really only be a diode (probably schottky from my meter readings)

Time to try and identify the SMD device labelled 'AJ' - again the list said that it could be almost anything, so I decided to pull one off the scrapped board and try and test it. Fiddly things these SMD chips - breath and they skid all over the place. In the end I super-glued it to a bit of wood, pressed pins in adjacent to the connections, and biased them together with a Hellerman rubber sleeve. Didn't do me any good - my component tester had no idea what it was. So I've drawn up just a block with three connections for the circuit drawing hoping that it's identity might be revealed by context.

I still have quite a few 10K resistors to positively tie to places in the diagram - several are definitely pull ups for gate inputs from the outside world, but I'll save to joy of finding them for tomorrow!
99
Tools / Re: tool tip No 2
« Last post by WeldingRod on August 29, 2021, 10:13:11 AM »
At one point made an excel chart with all the weird english drill sizes and 1/2mm sizes, in order with the decimal sizes.
I color coded the metric and fractional bits.  A very handy chart; I've got three on my shop walls.

Sent from my SM-G892A using Tapatalk

100
Tools / Re: tip of the day
« Last post by russ57 on August 29, 2021, 03:41:22 AM »
Another forum im on had a guy selling an angle grinder because "he didnt need 3"....

The shouts suggesting 4 or 5 to be the absolute minimum saw him withdrawing it from sale.
Metal cut off, metal grind, flap, wire wheel, tungsten cut off, plus at least one to be able to swap around, maybe a larger one,....

Although he was a wood guy.

-russ

Pages: 1 ... 8 9 [10]