andrew96

I can't believe it is working again! I am overjoyed! My mother did like this doorbell!!

ok so tr1 was faulty! its emitter had failed after 40 years!! replaced it and....... At this time...I am not ready to let the chip go as this was made and given to... and used by my mother on her door for over 30 years, and she sadly passed just after Christmas last year, so at the moment it holds a lot of memories. but if there is any non destructive testing I can do then yes I can do what I can to help. But at least it proves a 'special' different version of this chip was never produced, just this one

well reading through I found this info....... clock does the note pitch (which is 360khz on my pcb, not 400khz)and the R.C network for the note timing, K8 is the input, but R9 controls it via a transistor... hmmmmmm that's where I will look!

funny enough he was the author of the doorbell in the everyday electronics Feb 1979 edition where it goes in detail of how it all works!

ahhh!!!! I was hoping it was going to be the clock!! the article in the mag says it runs at 400khz, mine is running at 360khz so if anything should be slightly slow tunes!! so it definitely looks buggered!! But there is some good information on how it works in the magazine!

so it was actually in use as a doorbell for nearly 40 years before being removed for a wireless doorbell when it finally started playing up playing tunes! I vaguely remember it started to play the tunes fast! usually it meant the batteries were low and replacing them bought it back to working, but on the last battery change it didn't!! blimey what memories!! it appears to play the first note right, then go into 'manic' mode!

cool!! thanks!! feb 1979, I made this at age 14

I am actually quite amazed I soldered well way back then with only a antex 25w mains soldering iron!! sadly I don't think the chip will be any good, it doesn't play anything correctly now, its worse than when it was removed! I think battery vapours have taken its toll on it! I MAY even have the magazine inn the loft I made it from, If I do it will have a circuit diagram in it and I can look into seeing if its permanently bad, or if repairable

YEP!! I can confirm that is the EXACT tune the doorbell played! yes I still remember it well!!! My doorbell no longer plays tunes which is why it was decommissioned from my mothers front door several years back. I made it as a present back either in the late 70's or early 80's from a magazine 'everyday electronics', I also bought 'practical electronics' too but I am sure it was from 'everyday electronics'

back in the day when electronic magazines were the only information you could get! and postal orders ruled!!

OMG are you kidding me!!!!!! I actually bought one of those chips back in the day and made a doorbell Luckily I still know where it is! It indeed has the MP0027A chip I bought still in it I can confirm though the 'A' version has NO special different code inside it to non A version, it still plays the same tunes, typed on paper as it was before computers and ANY word processing! I typed it!! lol

yes, you should really read the FAQ for newbies, it tells you all you need to know. choose your files wisely! or donate

I fear sadly the SPace code is not going to be much help fpr MPS, Space is a Motorola processor and MPS is a Texas processor so wont be the same code sadly, but defiantly interesting!

yes a rom one would likely have that, but a masked rom doesn't! it is silicon etched permantly when the silicon wafer is made, no way of reading masked roms inside a cpu, it protects the manufacturers code 100%

complete information covering the cpu TMS7000_FamilyData_1986.pdf

Yes it was a masked rom version of the TMS7041 TMS7041.pdf

It was a few years ago now when I was into repairing them. It was one of those surplus suppliers, when its gone it's gone! they was new original stock too. I will see if I can find out where it was from through going through emails as I say it was a masked rom at manufacture, I remember I also looked into what the processor was and all that but cannot now remember what it was, I have looked in my pc folders to see if I downloaded any sort of datasheet on it, but I didn't. If I remember any more i will post

yes it is a masked rom inside the cpu, as you say no direct way of reading it out and far to expensive to get it dumped using the nitric acid and microscope technique. I did look into this using a version that had a cpu and a erasable rom section, but I could never find a hint of the internal code! the masked chips were available new a couple of years back at £15 each in the original antistatic tubes, but the seller would not budge on price so I only bought a few at that price. That really was the way they protected MPS technology from being easily copied!

Well this is it! everything helps for sure! I have also heard that barcrest sometimes used the same chr chip in different games, It could be they got a bit lazy towards the end when they knew MPU5 was on the way so they put less effort in perhaps, that's my guess!!

Oh cool!! it is these chinks in the armour that helps! sadly the BWB chr chip is a standard pal chip where thee Barcrest ones are not (they are a custom made device similar to a PAL but more complicated inside) thatnks again!

Ah thankyou, I did look at the github link but didn't see anything, but you have explained it well, thankyou (no worries I know I am on my own with real chr's)

Is there anything there that could help me with the differences between real and MFME? (Once the work on the boardmaster 4000 work is done, I am thinking of writing a testbasic program for it so it can get the real lamp tables out of real chr chips easily in a few seconds, this might speed along working out what is going on hopefully)

well I did buy my tester some years ago when you could get them from the states for character chip interrogating you just need a mpu4, power supply and connecting power lead and of course a character chip in a progtam cart, then the lamp tables can be read out using the fluke troubleshooter you can see why no one else has gone deep into looking at the character lamp tables!!

yeah and you still need the 6089 pod!, I think I paid £500 for the pod not working when I got one, they go for double that now

If anyone wants to do there own investigations in real character mpu4 chips then there is a fluke troubleshooter 9010 on ebay right now!, you will then just need the 6809 pod to plug into the mpu4 board to the troubleshooter https://www.ebay.co.uk/itm/125328711461