Re: MK14 schematic revisions
 

Happy Birthday!

That does seem astoundingly cheap, it's a shame around half of it is for carriage. It's not that long ago that to have a one-off or small run of PCBs made would have cost well into three figures, that's why nothing I make ever gets further than veroboard.

I'll drop you a PM about this later.

Re: MK14 schematic revisions
 

Happy Birthday to you... thanks for sharing that as at least I know what to expect in the way of costs when I eventually get to a PCB with the things I am working on... I I stand by my earlier offer to chip in with the cost and build one if you will permit me...

Re: MK14 schematic revisions
 

Hi! Sorry about the radio silence. The boards have arrived and look great, but I managed to hurt my back and have found it painful to sit up let alone scrabble about looking for components :)
I've offered a couple of you some of my spare components and I'm working on a "price list" as I discover components but it may be a while before I recover enough to find the rest.

Re: MK14 schematic revisions
 

Who knew working on MK14 projects would be so dangerous?

(I'm thinking foot / ankle problems last year, eye problems and now back problems). Maybe you need to take up a gentler pastime?

Will look out for a parts list from you presumably via PM or email - anything you can't currently find or reach, I'm sure I can have fun trying to unearth for myself. None of this is super urgent, and certainly not worth you wrenching your back (again) for.

Re: MK14 schematic revisions
 

I actually did my back in by lifting shopping bags out of a cart and into my car. Who knew milk and vegetables could be so heavy! I should go back to eating junk food, thats a lot safer!

Re: MK14 schematic revisions
 

Owch - had a week in bed once getting a sock out of the tumble dryer... hope it is better soon. I have quite a lot of odd parts already as well as I bought several of some chips and passives.

Re: MK14 schematic revisions
 

Well I've given this a thorough inspect and aside for a couple of trivial silkscreen errors (Dated 2018 not 2019, U11 label overprinting part no) all seems good.
(Sorry the images are a bit fuzzy I had to crop and compress them to death to get them under the 100k limit. If you want so see bigger images try http://www.ianrolfe.com/page/mk14-rev-vi-boards/)

Re: MK14 schematic revisions
 

In time, that minor screen print error may make these ones especially collectable, like banknotes or stamps with similar small errors. :)

Re: MK14 schematic revisions
 

Looking good, looks like an MK14 so it is an MK14 - over 40 years later - impressive achievement since that first advert in January 1978... in the Feb 1978 issue of Practical Wireless

I was going to link to American Radio but, the PDF links are broken for that magazine at the moment. So here is a capture...

Attachment 186864Attachment 186865

Re: MK14 schematic revisions
 

Been quiet on the MK14 front in here - just thought you may all be interested in the fact that one of Martin's reproduction Tape Interface PCB's with a BC107 rather than a 2N2926 (hfe 120 rather than 100 so I took a chance) works well (once I found the read LED was faulty...) on my JM Precision repro.

Seems that either the SCIOS save or the load routine do not handle the last byte of a 256 byte block... Unlike a Spectrum the system is happier at a much lower volume. It is also very sensitive to any clicks or noise so important you don't press GO until after the mechanism settles, the first bit is corrupt or the whole data stream slips.

Using the Sanyo M1104X on batteries as recommended by SOC - on this repro board there is no R11 (27k) in series with D1 - I used a 1N4148 as it is not named in the manual. The clip on the resistor is just a handy place to pick up 5V and still allow the expansion connector to be removed easily. The white wire loops SIN and SENSEB. GROUND, SENSEB and FLAG0 are soldered on the connector.

Attachment 188671

Re: MK14 schematic revisions
 

There's a fine line between taking a keen interest and outright hassling someone so I've resisted the temptation to ask Slothie how he is faring with his latest repro PCBs.

On my (original) cassette interface I see that I changed C1, the audio input capacitor, to a lowish value polystyrene type which would have been more at home in a radio project. The obvious intention was to attenuate the input and shave off the low frequency end of the incoming, so maybe I had problems with mains hum and low frequency rumble coming out of the particular tape recorder that I used. SOC recommended using battery powered recorders, as you have pointed out.

One other thing to watch for on original MK14 cassette interfaces, the PCB screen printing for the orientation of the diode D1 was originally the wrong way around, although I believe the circuit diagram always showed it correctly oriented - but if anyone happens to buy an original example it might be worth checking the orientation of that diode just in case the diode was inserted as per the screen printing. Later runs of the cassette interface PCB may have had that error corrected, as well.

Incidentally the (original) diode on my interface is ... a 1N4148, identified by rings in the resistor colour code rather than with printed numbers as per more modern versions.

Re: MK14 schematic revisions
 

Hi folks, my back is recovered now but it effectively knocked me out for 5 weeks and I'm having to catch up with everything I couldnt do while laid up in bed. I haven't so much as soldered a single joint but I have come across some of the missing parts (including the displays!) while doing other things so I'll be finishing off the parts lists and getting them out soon.

Re: MK14 schematic revisions
 

Glad you are on the mend... I still have not found my 'missing' spare SC/MP and 8154, although I have not really looked very hard yet. My own fault really, I've known exactly where they have been for the past 10 years or so (at work) and I only recently thought I had better move them to a 'safe' place more under my direct control. No idea where I've put them.

Re: MK14 schematic revisions
 

Ah yes, I'm always putting things in a "safe place" that I've been tripping over for years then a few weeks later needing them and not being able to remember where I moved them to. That's why tidying is always a dangerous move!

Re: MK14 schematic revisions
 

Exactly what I keep telling SWMBO.

Still haven't found them, though. I will mount a concerted attack on this problem once I've done all those other things I still haven't done.

Re: MK14 schematic revisions
 

Slothie glad to hear about the Back being better. I have been absent due to a significant stint in hospital and I am still laid up and find it difficult to use a computer - or sort through the chaos of my study for anything - I like you both, know where everything is in the mess until I dig it out and then remember I moved it last time I found it but, cant remember where too.. Speak soon.

Re: MK14 schematic revisions
 

Wow, I hope this is not some sort of Phaerohic MK14 curse which I'm about to become the third victim of - best wishes and a speedy recovery for you both.

Re: MK14 schematic revisions
 

Well I had just finished getting my MK14 tape interface to work and save/load successfully... Hmmm

Thanks Sirius... maybe I should delay building the VDU until I fully recover.

Re: MK14 schematic revisions
 

Tim, you mentioned somewhere (I think) that you thought the cassette routines were failing to work with (Save? Load?) the 256th byte of 256 saved bytes.

I know there isn't much information that you don't absorb, but did you notice the bit in the tape interface manual where it says that if you want to save a full 256 bytes, you have to enter '00' as the number of bytes to be saved?

Re: MK14 schematic revisions
 

Its worse than that, ive been in hospital for the last 3 months which is why Ive been silent. Ive been diagnosed with miloma, s type of bone marrow cancer whi h lucky for me is treatable. However i have had to move out of my flat because its unsuitable for me on my return because of the stairrs and because i won't. Be able to work for some time, so everything is going into storage. When I have access to my laptop i will upload the gerbers etc for tbr pcb in case someone wants to give it a try.