Help Needed with 6502 Second Processor

[dhoggan]

Hi everyone,

A bit on a Bank Holiday conundrum for you! I have finally found some time to set up the 6502 second processor I recently received from eBay, but seem to be having issues.

Currently I have the ROM sockets set up as follows: <OS>, <DNFS>, blank, blank, <BASIC>. I'm pretty sure the DNFS ROM is OK as I can access a floppy drive. The issue is that, when I power on the second processor and then the Beeb, I hear the first beep and then the caps and shift LEDs just stay on and the the system appears hung. With the second processor powered off, the Beeb works as expected.

I'm pretty sure I have the short IDC cable plugged in the right way - the small line up on the same side as the one next to the Tube connector.

And ideas? The fact that the Beeb hangs when the processor is tunrned on suggests it's PSU is working, but I've no idea what to check next.

Thanks,

Dave

[geraldholdsworth]

My first instinct would be to take the top off the co-pro box and make sure everything is seated OK.

[dp11]

try unplugging an replugging the 40pin tube connector a few times. We have seen oxide on the pins cause problems as they haven't been used in 30+years

[BigEd]

It's common to have a bad connection, if the Tube connector on the Beeb has never been used. So the advice is to plug and unplug the cable several dozen times, and maybe even clean the pins with the hard kind of pencil eraser. Or more drastically, with a screwdriver:
viewtopic.php?p=203086#p203086

[cmorley]

Or more drastically, with a screwdriver:

Or 1 squirt with contact cleaner for the more gentle approach.

[dhoggan]

Hi,

I've just gone to try these suggestions and have noticed that there is a small break in one of the cable making up the 40-way IDC cable - it's one of the outer tracks.

Can anyone recommend a source of a new cable? I could try making one up but I'm not wonderfully adept at these things. If there isn't a way to buy a new cable (given it is an old item), could someone help in pointing me in the direction of the shopping list of bit's I'll need? On the positive side, I could then get a cable with a bit more slack in it.

Thanks,

Dave

[Kazzie]

Hi,

I've just gone to try these suggestions and have noticed that there is a small break in one of the cable making up the 40-way IDC cable - it's one of the outer tracks.

Can anyone recommend a source of a new cable? I could try making one up but I'm not wonderfully adept at these things. If there isn't a way to buy a new cable (given it is an old item), could someone help in pointing me in the direction of the shopping list of bit's I'll need? On the positive side, I could then get a cable with a bit more slack in it.

Thanks,

Dave

The most common use of 40-pin IDC cables is in connecting IDE hard drives to their controller cards. You might happen to have one in a drawer or box somewhere. (Some of the more recent ones use 80 conductors for 40 pins, I don't know if those would be problematic.)

An example of a using an IDE cable can be seen at https://www.retro-kit.co.uk/page.cfm/co ... Processor/

[1024MAK]

The most common use of 40-pin IDC cables is in connecting IDE hard drives to their controller cards. You might happen to have one in a drawer or box somewhere. (Some of the more recent ones use 80 conductors for 40 pins, I don't know if those would be problematic.)

An example of a using an IDE cable can be seen at https://www.retro-kit.co.uk/page.cfm/co ... Processor/

The more modern IDE / PATA 80 way cables are NOT suitable.
You need a normal standard 40 way ribbon cable fitted with standard IDC 40 way connectors. If the connector has any pins blanked off (or plugged), it’s not suitable.

Alas, these days trying to work out what is sold on the likes of eBay is really hard when it comes to IDE / PATA cables

Around five years ago I managed to get one that was suitable, IIRC it was sold as a CD-ROM cable (although what I wanted it for had nothing to do with the TUBE or second processors).

One important point to make, is that there is a reason that the cable is not very long. So although you can get a slightly longer one made up, don’t make it too long. Otherwise the TUBE interface and the communication to/from the second processor may become unreliable.

Mark at RetroClinic may be able to help. The correct ribbon cable and the correct IDC connectors are still made and still sold by electronic suppliers.

Mark

[dhoggan]

Ah yes, I remember them but alas I do not have any to hand. Before I go off an buy one however, from the link you provided it seems to suggest that I would have to replace the IDC connector on the second processor board? I am I reading that wrong - can I simply use a normal 40 IDC cable with no mods?

Thanks,

Dave

[1024MAK]

BeebMaster has a lot of photos of second processors here.

As you can see in his photos, IDC / PCB translation connectors are used to connect the ribbon cable to the PCB.

Note, since you posted, I have edited my earlier post.

Mark

[BeebMaster]

I can supply a 40-way IDC female-female cable suitable for the Tube. Just check that the cable is in fact detachable at the second processor end, I am sure that on some cheese wedges the cable is soldered to the board.

[dhoggan]

Yes, I have had a look inside and the IDC connector is soldered to the board, so complicates replaces a little bit - I'm assuming that this is the translation connector you referred to?

As for additional length, that makes sense, but even an extra 10cm would be really hand, if possible.

Based upon what I've seen, if Mark can help I'm hoping to be able to send him the board and have him replace the cable.

I'll let you all know how it goes

Dave

[dhoggan]

Mr BeebMaster,

Just saw your post after my last one.

Inside the second processor the connector is attached to the board - so either it has to be desoldered or the IDC cable extracted from the connector and a new one inserted. It's not a straight swap on this unit I'm afraid.

Thanks,

Dave

[Elminster]

Or more drastically, with a screwdriver:
viewtopic.php?p=203086#p203086

I deny (edit) everything. Although I Have used the screwdriver/carbon fibreglass pencil combo several times and always does the job. Sometimes I think maybe a Dremel.

[1024MAK]

Yes, I have had a look inside and the IDC connector is soldered to the board, so complicates replaces a little bit - I'm assuming that this is the translation connector you referred to?

As for additional length, that makes sense, but even an extra 10cm would be really hand, if possible.

Based upon what I've seen, if Mark can help I'm hoping to be able to send him the board and have him replace the cable.

I'll let you all know how it goes

Dave

Sorry, I should have said “transition” connector

Here is one available at Farnell.

Mark

[eXne]

Dave,

As you’ve spotted a damage wire you might strip the wire around the damage and solder a wire as a bypass.
This way you can easily check if this is the only fault.
You need to be careful and a bit handy with soldering.

Etienne

[dhoggan]

Hi everyone,

I'm looking at replacing the fixed IDC connector on the 6502 board with an IDC box header (the type which has the latch on one side) so I can then use a standard 40-way IDC cable.

However, as I've been trying different things in between work commitments, I've manage to lose/forget the cable orientation between 6502 board and the BBC Tube port. So, assuming the 40-way cable is latched, should the IDC header have the gap pointing toward the back of the 6502 case, or toward the PSU?

Thanks,

Dave

[DigitalDunc]

I don't know if you still need to know, but as I've just had to replace the ribbon on mine, I can show you. The cutout should be to the front of the case with pin one on the left. Take note of where my biro is pointing as that end is pin one. You'll also find that the IDC plug has a little mark denoting pin one on it to helpfully guide whoever crimps it on.

One final note, I will learn from whoever has more experience and knowledge than me as I'm sure I don't know everything.

EDIT: I forgot to mention that the board has a chunky ground plane occupying some of the pins making desoldering a pain. I was waving an iron at it at the same time as my desoldering gun just to get the holes clear.

[1024MAK]

The end with pin 1 is often marked with a small triangle embossed into the plastic housing of the IDC or box header connector.

Mark