Beeb Resurrection - 2nd scope attempt!

discuss both original and modern hardware for the bbc micro/electron
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leenew
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Beeb Resurrection - 2nd scope attempt!

Post by leenew » Wed Mar 19, 2014 11:00 am

Hi,
Here's another from my duffer pile.
Doing the same checks from page 48 of the Service manual as I did before I find:

Pin 40 of the 6502 is high and goes low on break.
I have the 1,2,4 and 8mhz signals on the vidproc
but on the 6502, pin 3 is LOW and pins 4,7 and 37 are high
I am getting signals on pin 39 of IC2 and maybe a pulse on pin 40 of IC2.

What does this tell me? :D

Thanks,

Lee.

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Re: Beeb Resurrection - 2nd scope attempt!

Post by duikkie » Wed Mar 19, 2014 11:41 am

a long beeeeeeep ?? :lol:
how many off broken beeb's do you have ?
i will check what i think can be the problem
in mean time :
your 6502 is not broken ??
check ic30, ic34, ic 29.


leenew wrote:Hi,
Here's another from my duffer pile.
Doing the same checks from page 48 of the Service manual as I did before I find:

Pin 40 of the 6502 is high and goes low on break.
I have the 1,2,4 and 8mhz signals on the vidproc
but on the 6502, pin 3 is LOW and pins 4,7 and 37 are high
I am getting signals on pin 39 of IC2 and maybe a pulse on pin 40 of IC2.

What does this tell me? :D

Thanks,

Lee.

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Re: Beeb Resurrection - 2nd scope attempt!

Post by 1024MAK » Wed Mar 19, 2014 11:52 am

Hi Lee :-)
leenew wrote:Here's another from my duffer pile.
If you don't mind me asking, how tall is this "duffer pile"?
leenew also wrote:Pin 40 of the 6502 is high and goes low on break.
I have the 1,2,4 and 8mhz signals on the vidproc
All good so far...
But
Then leenew wrote:on the 6502, pin 3 is LOW and pins 4,7 and 37 are high
Not good :(
The CPU (6502) will just act as a small heater without a good clock input (pin37). Use your 'scope and check the pins on IC30 (74LS74), IC34 (another 74LS74) and IC29 (74LS32). These are all part of the 2MHz and 1MHz clock switching circuits.
Phew, leenew wrote:I am getting signals on pin 39 of IC2 and maybe a pulse on pin 40 of IC2.
Until the CPU has set-up the 6845's registers to the correct values, it will operate with its power on default values. The data sheet should tell you more.

Edit: Ah, Duikkie got in just before me :mrgreen:
Mark

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Re: Beeb Resurrection - 2nd scope attempt!

Post by duikkie » Wed Mar 19, 2014 12:04 pm

how far can you count leenew ?? pin7 , not used you mean pin 6 ??

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Re: Beeb Resurrection - 2nd scope attempt!

Post by duikkie » Wed Mar 19, 2014 12:44 pm

something to add
to get a signal on a pin is not allways good
it is the quality of the signal
...................................... __ ................ ^
make sure your 8 mhz is nice __| |__ and not __| |^___ or something like that
a little ~~ will not hurt but no sharp spikes.

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Re: Beeb Resurrection - 2nd scope attempt!

Post by leenew » Wed Mar 19, 2014 12:49 pm

Where's the best place to test the 8mhz Duikkie?

Pin7 of IC6 looks OK and pin 3 of IC44.

It isn't square though - it is saw-tooth ^^^^^^^

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Re: Beeb Resurrection - 2nd scope attempt!

Post by leenew » Wed Mar 19, 2014 1:00 pm

I have swapped the 74LS74 at IC34 for a DM74LS74AN is this OK?
Now I get signals on the 6502 pins 3 4 and 37
this signal is present on pin 10 of IC33 but it is 'dirty' at the top??

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Re: Beeb Resurrection - 2nd scope attempt!

Post by leenew » Wed Mar 19, 2014 1:19 pm

pin 34 of 6502
20140319_131837[1].jpg
pin 10 IC33
20140319_131849[1].jpg
pin 4 6502 seems stuck high.

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Re: Beeb Resurrection - 2nd scope attempt!

Post by 1024MAK » Wed Mar 19, 2014 2:06 pm

leenew wrote:I have swapped the 74LS74 at IC34 for a DM74LS74AN is this OK?
Now I get signals on the 6502 pins 3 4 and 37
this signal is present on pin 10 of IC33 but it is 'dirty' at the top??
In most applications, any make of 74LS74 can replace any make of 74LS74. But keep in mind, in some circuits (including the Beeb), some makes of 74LS74 perform better than others.
If the signals at the 6502 are now okay (shape edges and driving to "TTL spec" levels), yes, most likely it is okay.

The output, pin 10 of IC33, is R/nW and goes all over the board. It is not surprising that the line has some noise on it. Is the input, on IC33 pin 11 okay?

Mark

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Re: Beeb Resurrection - 2nd scope attempt!

Post by leenew » Wed Mar 19, 2014 2:22 pm

Pin 11 looks OK
You have to bear in mind though that I don't actually know what I am doing :D
It may be a nice, perfect shaped, totally incorrect signal :D
I am getting pulses peaking at 4V about 8us apart.

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Re: Beeb Resurrection - 2nd scope attempt!

Post by 1024MAK » Wed Mar 19, 2014 2:33 pm

Remember, this is the signal from the CPU to tell the rest of the system (memory and I/O circuitry) if data on the data bus is being output from the CPU, or if the CPU is expecting the system to put data on the data bus (for input / reading by the CPU).

For most fault finding, as long as the signal is changing state, has a good shape, and switches between "TTL" levels, that's all you normally need to know.

Mark

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Re: Beeb Resurrection - 2nd scope attempt!

Post by duikkie » Wed Mar 19, 2014 2:36 pm

hang on i am trying to found all your ic on the map :)

but my iss7 problem was ic81 from disc drive , bad signals can come from every where

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Re: Beeb Resurrection - 2nd scope attempt!

Post by duikkie » Wed Mar 19, 2014 2:47 pm

i don't like the spike on the mountain from his pictures, i had the same but on the front of the mountain. some ic is makinging a spike.

it must look like page 49 of your bbcmicrocomputer service manual

is the spike also on pin 12/11 from ic33 ??
1024MAK wrote:Remember, this is the signal from the CPU to tell the rest of the system (memory and I/O circuitry) if data on the data bus is being output from the CPU, or if the CPU is expecting the system to put data on the data bus (for input / reading by the CPU).

For most fault finding, as long as the signal is changing state, has a good shape, and switches between "TTL" levels, that's all you normally need to know.

Mark

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Re: Beeb Resurrection - 2nd scope attempt!

Post by duikkie » Wed Mar 19, 2014 2:48 pm

is this pin 11 from ic 33 ??
leenew wrote:Pin 11 looks OK
You have to bear in mind though that I don't actually know what I am doing :D
It may be a nice, perfect shaped, totally incorrect signal :D
I am getting pulses peaking at 4V about 8us apart.

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Re: Beeb Resurrection - 2nd scope attempt!

Post by duikkie » Wed Mar 19, 2014 2:50 pm

why do english people put there scoop like that , i do have already have neck problems :)

i have tuned it is not the mountain , but the valley , grrrrrrr
the bbc can handle that i think

still beeeeeeeeeeeeeeeeeeep or do you have picture ?

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Re: Beeb Resurrection - 2nd scope attempt!

Post by leenew » Wed Mar 19, 2014 2:55 pm

Ha Ha, it's just my phone always makes photos some out sideways when I upload them....
The pin 11 IS IC33 yes.
pins 11 and 12 of IC33 look a lot cleaner.

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Re: Beeb Resurrection - 2nd scope attempt!

Post by duikkie » Wed Mar 19, 2014 3:01 pm

turn your phone 90 degrees :mrgreen:
which iss board is it one where ic77 is on socket ??
leenew wrote:Ha Ha, it's just my phone always makes photos some out sideways when I upload them....
The pin 11 IS IC33 yes.
pins 11 and 12 of IC33 look a lot cleaner.

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Re: Beeb Resurrection - 2nd scope attempt!

Post by duikkie » Wed Mar 19, 2014 3:18 pm

oke if no beep,beep from bbc b yet

you can try to clean up the R/nW signal

AND OF CAUSE if it's a iss 7 board IC14

we have a ic77 for the discdrive and game port ( near by econet chip)
then we have ic69 the userport chip
then ic72 the buffer for 1mhz bus

if still not wordking
ic3 the keyboard chip
then the ic2 chip

take one at the time out look at signal on pin 10 ic33 everytime
ic2 last one because then no picture

i see also ic29 that for ram

econet ?? chip ic89
ic 4 for cass

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Re: Beeb Resurrection - 2nd scope attempt!

Post by duikkie » Wed Mar 19, 2014 3:27 pm

check if all links are there !!

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Re: Beeb Resurrection - 2nd scope attempt!

Post by leenew » Wed Mar 19, 2014 4:31 pm

Hi,
All the links are there.
I have just been swapping chips around from a working machine to make sure everything is ok.
IC1, IC2, IC3 and IC6 are all OK.
IC14 is ok.

It is an issue 7 board.
The DFS chips are soldered to the board but there is no DFS ROM or 8271 fitted.
I don't think this will stop it booting though.
In fact I have just put an 8271 and A DFS ROM in and it still doesn't boot, and I have taken the 8271 and DFS ROM OUT of the working one and it still boots.

IC77 is soldered in. IC33 is soldered in.
IC69 is not fitted at the moment although this isn't needed to boot the machine.

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Re: Beeb Resurrection - 2nd scope attempt!

Post by paulv » Wed Mar 19, 2014 4:38 pm

What's the state of the S9 link?

Paul

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Re: Beeb Resurrection - 2nd scope attempt!

Post by leenew » Wed Mar 19, 2014 4:54 pm

Hi Paul,
S9 is open, just the original 2 solder pads.
I know really I should close this but would it stop it booting??

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Re: Beeb Resurrection - 2nd scope attempt!

Post by leenew » Wed Mar 19, 2014 4:59 pm

Just noticed that IC33 isn't a 74LS04 but a 733w01672 with a cap soldered between pins 13 and 14.

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Re: Beeb Resurrection - 2nd scope attempt!

Post by paulv » Wed Mar 19, 2014 5:00 pm

It should be open when the 8271 is fitted and closed when not AFAIK otherwise things won't operate correctly.

As a starter for ten, remove the DFS and 8271 and close the link. That way you're at least running the machine with the correct link config without the hardware fitted.

Paul

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Re: Beeb Resurrection - 2nd scope attempt!

Post by paulv » Wed Mar 19, 2014 5:08 pm

leenew wrote:Just noticed that IC33 isn't a 74LS04 but a 733w01672 with a cap soldered between pins 13 and 14.
That's a part number rather than a chip type. I take it it's a National Semi-conductor manufactured chip?

As for the cap, seems odd to have a cap between +5v and an input rather than to GND as a decoupling cap. I've not seen that before, not that that means much!

If it were me, if it's not on the schematic, I'd remove it and see what difference that makes.

Paul

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Re: Beeb Resurrection - 2nd scope attempt!

Post by leenew » Wed Mar 19, 2014 5:13 pm

OK, link closed with no DFS ROM and no 8271 but the ancillary DFS chips are still in (soldered in)

IC33 could be a a SP8428 then??
I have looked at a few beebs and I DO have another with this chip - including the cap!

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Re: Beeb Resurrection - 2nd scope attempt!

Post by 1024MAK » Wed Mar 19, 2014 5:35 pm

leenew wrote:OK, link closed with no DFS ROM and no 8271 but the ancillary DFS chips are still in (soldered in)
Err... Either S9 is fitted and the 8271 is not fitted, or S9 is NOT fitted and the 8271 is fitted. Otherwise the /NMI line will not work and this can cause problems....
leenew also wrote:IC33 could be a a SP8428 then??
That looks like a batch date (84 is the year, 28 is the week).
leenew also wrote:I have looked at a few beebs and I DO have another with this chip - including the cap!
For now, I would leave the cap alone. it may be there to slow the signal.

Mark

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Re: Beeb Resurrection - 2nd scope attempt!

Post by leenew » Wed Mar 19, 2014 6:04 pm

That's right Mark,
I had an 8271 and a DFS ROM in (link S9 open) but removed the chips for testing.
I have now soldered closed S9 on Paul's advice.
I can't remove the ancillary DFS chips IC79, 80, 81 etc. as they are soldered in.
If you like, I could put the 8271 back, and the DFS ROM, and snip the link again? :D

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Re: Beeb Resurrection - 2nd scope attempt!

Post by leenew » Wed Mar 19, 2014 6:08 pm

for the record:
20140319_180801[1].jpg
err... the baby is nothing to do with it, I can't remove it now!!! :lol:
Attachments
20140315_180332[1].jpg
Last edited by leenew on Wed Mar 19, 2014 6:33 pm, edited 3 times in total.

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Re: Beeb Resurrection - 2nd scope attempt!

Post by 1024MAK » Wed Mar 19, 2014 6:20 pm

leenew wrote:That's right Mark,
I had an 8271 and a DFS ROM in (link S9 open) but removed the chips for testing.
I have now soldered closed S9 on Paul's advice.
I can't remove the ancillary DFS chips IC79, 80, 81 etc. as they are soldered in.
If you like, I could put the 8271 back, and the DFS ROM, and snip the link again? :D
Until you get the machine working, leave the 8271 and DFS ROM out.

Mark

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