Page 2 of 3

Re: My new board

Posted: Tue Jul 01, 2014 1:11 pm
by drgeoff
Unsoldering from single layer boards is much easier than from ones with plated through holes.

Re: My new board

Posted: Tue Jul 01, 2014 1:22 pm
by klricks
mrpi64 wrote:Sorry, if I didn't make it clear - it's an idea for the future, not for just now.
Time or future does not make obsolete components better.... it's worse....

If there are any 74xxx series TTL or 4000 series CMOS chips then they may be useful for experiments or learning how digital logic works.

In my experience, trying to de-solder DIP chips with a single tip soldering iron is a lesson in futility especially in 4+ multi layer boards.

Hot air / vacuum de-soldering tools are quick and easy but rather expensive, though there is now a lot of cheap soldering equipment available out of China.

I have also used de-soldering alloy. This is a special solder alloy that is mixed with the solder at each pin. The alloy significantly lowers the melting point of the existing solder to where the solder will remain molten for several seconds giving enough time to pull the chip out. Works very well but is kind of expensive.

I have never seen a heat sink that would work on chip pins .... only for transistor leads and such. Most rework is aimed a replacing a faulty components on a board without damaging the pads. Not trying to salvage components for use elsewhere.

Re: My new board

Posted: Tue Jul 01, 2014 1:29 pm
by Richard-TX
When I worked at AT&T/CS/USL there was a S100 based computer in the basement that ran Unix. I never bothered to to fire it up. It seemed so pointless when I had oddles of 3B2-600's and Starservers to play with.

Re: My new board

Posted: Tue Jul 01, 2014 2:52 pm
by mrpi64
MrEngman wrote:Hre's a few ideas for desoldering http://en.wikipedia.org/wiki/Desoldering

I have used a solder sucker often in the past to unsolder DIL devices without damaging them. Solder wick is also useful.


MrEngman
Thanks. I have tried a desoldering pump, but they don't work such a treat for me - there is always just a bit left. Of course, that's what the desoldering wick is for.

Re: My new board

Posted: Tue Jul 01, 2014 2:53 pm
by mrpi64
klricks wrote:
mrpi64 wrote:Sorry, if I didn't make it clear - it's an idea for the future, not for just now.
Time or future does not make obsolete components better.... it's worse....

If there are any 74xxx series TTL or 4000 series CMOS chips then they may be useful for experiments or learning how digital logic works.

In my experience, trying to de-solder DIP chips with a single tip soldering iron is a lesson in futility especially in 4+ multi layer boards.

Hot air / vacuum de-soldering tools are quick and easy but rather expensive, though there is now a lot of cheap soldering equipment available out of China.

I have also used de-soldering alloy. This is a special solder alloy that is mixed with the solder at each pin. The alloy significantly lowers the melting point of the existing solder to where the solder will remain molten for several seconds giving enough time to pull the chip out. Works very well but is kind of expensive.

I have never seen a heat sink that would work on chip pins .... only for transistor leads and such. Most rework is aimed a replacing a faulty components on a board without damaging the pads. Not trying to salvage components for use elsewhere.
Almost every small chip that doesn't look important on that board is a logic device. There are quite a few Octal TX/RX buffers.
And isn't there a kind of copper braid that "sucks" the solder?

Re: My new board

Posted: Tue Jul 01, 2014 3:15 pm
by mrpi64
drgeoff wrote:
mrpi64 wrote:The AT&T chip is a "Field-Programmable Gate Array".
I'm not aware* that AT&T ever made FPGAs so if the chip really is a FPGA I'd surmise that the logo is on it because it is 'programmed' to perform some logic that AT&T required. Much less chance of it being part of a 'computer' than telco switching or transmission equipment.

(I would expect some clues as to the original maker of the 'virgin' FPGA to be on the package.)

* does not mean they do/did not - I'm not aware of everything. :)
This chip is now made by Lattice semiconductor.

Re: My new board

Posted: Thu Jul 03, 2014 7:32 am
by mrpi64
As I said, would it be worth taking apart, and using the parts, or keeping it as it is?

Re: My new board

Posted: Fri Jul 04, 2014 3:36 am
by mjtessmer
Can you post better pictures of the board? (Top and bottom)
Does the board have any video IC's? Try powering up board.

Re: My new board

Posted: Fri Jul 04, 2014 7:34 am
by mrpi64
Apparently, it worked fine when removed (not so sure about that now ;) ), and I have no Multibus based Computer (actually, no computer at all), there is no video IC, but there is a serial controller.
There also is:
8KB Dynamic RAM
2x Floppy drives
1x SCSI bus
Some small LEDS (which all definetly work)
An RTC
A DMA Controller
An FPGA

Re: My new board

Posted: Fri Jul 04, 2014 10:10 am
by MrEngman
On my first computer board, a Motorola MC6809 development board, it only had a serial port. I ended up connecting it up to an old teletype at 110 baud. A little slow compared to these days but the nice thing though was the teletype included a paper tape reader/punch so I could save programs to paper tape and load them back as necessary. That was around 1975/6.

Connect it to a serial port and see what happens. Only problem is figuring out the baud rate but 9600 would probably be a good start.


MrEngman

Re: My new board

Posted: Fri Jul 04, 2014 12:24 pm
by mrpi64
Problem is, there is no serial port.

Re: My new board

Posted: Fri Jul 04, 2014 1:12 pm
by MrEngman
mrpi64 wrote:Problem is, there is no serial port.
So what about the serial controller. Doesn't it have some sort of output so one of the connectors?



MrEngman

Re: My new board

Posted: Sun Jul 06, 2014 1:16 pm
by mjtessmer
If there is a serial controller on the board, look for some MC1488's and MC1489's (TTL to RS232 level converters). You do not need a "multibus computer", just need a 86pin connector to provide power.

Re: My new board

Posted: Sun Jul 06, 2014 8:21 pm
by drgeoff
mjtessmer wrote:If there is a serial controller on the board, look for some MC1488's and MC1489's (TTL to RS232 level converters). You do not need a "multibus computer", just need a 86pin connector to provide power.
Don't even need the connector if you consult http://www.techfest.com/hardware/bus/multibus_sokos.htm for where on the board to solder leads for +12, +5, 0, -5 and -12 volt supplies.

Re: My new board

Posted: Mon Jul 07, 2014 7:18 am
by mrpi64
I have put up some better pictures, see my original post.
Also, eBay gem:
http://www.ebay.co.uk/itm/PHILIPS-CPU-S ... 3391042f20

Re: My new board

Posted: Mon Jul 07, 2014 8:08 am
by Ravenous
mrpi64 wrote:Also, eBay gem:
Looks pretty useless to me. Do you have any circuits for it?

Re: My new board

Posted: Mon Jul 07, 2014 9:59 am
by mrpi64
Ravenous wrote:
mrpi64 wrote:Also, eBay gem:
Looks pretty useless to me. Do you have any circuits for it?
Well, if you wanted to build a homebrew computer, it would be fantastic - it has built in I2C, UART, DMA/MMU, Timer, e.t.c, so it drastically reduces the amount of circuitry required. It is also fully object code compatible with the 68000.

Re: My new board (With better pictures)

Posted: Mon Jul 07, 2014 10:12 am
by Ravenous
Let me correct myself (I was being far too harsh with "Useless")

Before buying this you should defintely have a look and see exactly what's involved in building a working system. Including the tricky stuff like board layout and soldering.

Although there's probably all of the knowledge required from some of the experts on this forum, adding up all of the bits you'll need it might get much more expensive for a one-off build.

Anyway I think the right datasheet is here (I've only skimmed it very briefly):
http://pdf1.alldatasheet.com/datasheet- ... CCA84.html

Re: My new board

Posted: Mon Jul 07, 2014 11:39 am
by mahjongg
drgeoff wrote:Unsoldering from single layer boards is much easier than from ones with plated through holes.
True, in the past when I needed to desolder large amounts of components from a multi-layer scrapboard I used a locking plier
Image
clamped (softly) on the component: Then placed the board upside down with the locking plier hanging from the component, then heating the back of board from the top, locally with a handheld burner
Image
until the plier with the component fell out of the board.

Do not tighten the locking plier too much or the component, made soft by the heat, will be bent and become useless.

For smaller SMT components like SO-16 IC's I simply knocked them off the board after heating from the back with the same burner.

This method normally was the best and most efficient way to get the most components off the board undamaged.

I used this methods to desolder dozens of 74HCxx series DIP IC's from scrap boards.

Re: My new board

Posted: Mon Jul 07, 2014 2:23 pm
by drgeoff
MrEngman wrote:I have used a solder sucker often in the past to unsolder DIL devices without damaging them.
1. Techniques for removing a duff chip for replacement by another are not necessarily the same as those for removing a good chip for use again elsewhere.

2. A solder sucker needs to be held at just the right distance from the joint. Too far away and it doesn't suck the molten solder. Too close and the recoil action when the piston is released causes the nozzle to strike the board potentially damaging the pad if that is a concern.

Re: My new board (With better pictures)

Posted: Mon Jul 07, 2014 2:30 pm
by drgeoff
The board is probably rather less powerful in compute terms than a RPi but consumes several times as much power. It does have some more specialised I/0 but lacks the simplicity and universality of USB (and ethernet?).

Each to his own, but in my eyes neither the intact board nor the parts that can be salvaged are really worth the trouble!

Re: My new board

Posted: Mon Jul 07, 2014 2:46 pm
by MrEngman
drgeoff wrote:
MrEngman wrote:I have used a solder sucker often in the past to unsolder DIL devices without damaging them.
1. Techniques for removing a duff chip for replacement by another are not necessarily the same as those for removing a good chip for use again elsewhere.

2. A solder sucker needs to be held at just the right distance from the joint. Too far away and it doesn't suck the molten solder. Too close and the recoil action when the piston is released causes the nozzle to strike the board potentially damaging the pad if that is a concern.
I used to use the solder sucker to remove components to use again, not to junk them. e.g. PLDs that I wanted to change the programming of when they were solder directly into the board instead of fitted using a DIP socket.

And , yes, you have to be careful using it or else it can cause damage. However, where I worked i had no other option and so became reasonable proficient.



MrEngman

Re: My new board (With better pictures)

Posted: Mon Jul 07, 2014 4:47 pm
by mrpi64
Ravenous wrote:Let me correct myself (I was being far too harsh with "Useless")

Before buying this you should defintely have a look and see exactly what's involved in building a working system. Including the tricky stuff like board layout and soldering.

Although there's probably all of the knowledge required from some of the experts on this forum, adding up all of the bits you'll need it might get much more expensive for a one-off build.

Anyway I think the right datasheet is here (I've only skimmed it very briefly):
http://pdf1.alldatasheet.com/datasheet- ... CCA84.html
I was planning to use a matrix/eurocard board, and a DIN 41612 connector backplane to connect all of them together, like this. Does the board layout matter? I know that it can become a mess without some sensible layout.

Re: My new board

Posted: Mon Jul 07, 2014 4:48 pm
by mrpi64
mahjongg wrote:
drgeoff wrote:Unsoldering from single layer boards is much easier than from ones with plated through holes.
True, in the past when I needed to desolder large amounts of components from a multi-layer scrapboard I used a locking plier
Image
clamped (softly) on the component: Then placed the board upside down with the locking plier hanging from the component, then heating the back of board from the top, locally with a handheld burner
Image
until the plier with the component fell out of the board.

Do not tighten the locking plier too much or the component, made soft by the heat, will be bent and become useless.

For smaller SMT components like SO-16 IC's I simply knocked them off the board after heating from the back with the same burner.

This method normally was the best and most efficient way to get the most components off the board undamaged.

I used this methods to desolder dozens of 74HCxx series DIP IC's from scrap boards.
I don't think that anyone will trust me with a gas torch ;) but I think a soldering iron and some desoldering braid will do the job OK for now.

Re: My new board (With better pictures)

Posted: Mon Jul 07, 2014 4:52 pm
by mrpi64
drgeoff wrote:The board is probably rather less powerful in compute terms than a RPi but consumes several times as much power. It does have some more specialised I/0 but lacks the simplicity and universality of USB (and ethernet?).

Each to his own, but in my eyes neither the intact board nor the parts that can be salvaged are really worth the trouble!
Well, I don't really want to replicate a Pi - things like USB are a bit too modern for what I want. I want a pure old-school computer. There is serial on the board, But I can use that for ther peripherals for the board, as the 68070 has build-in UART. I want to use a terminal emulator (using the Pi's built-in UART, possibly) for terminal emulation (what else?), and the floppy disk controller & SCSI controller will let me to use mass storage, and attach some other things using the SCSI (scuzi) bus that I don't have to make. I may use the VME bus, as I can then buy some other manufactured boards from yesteryear that are designed for it (if there are any).