Beeb Resurrection - 2nd scope attempt!

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Re: Beeb Resurrection - 2nd scope attempt!

Post by 1024MAK » Thu Mar 20, 2014 4:02 pm

duikkie wrote:mark what do you think about the d16,d17,d18 and r114 circuit ?
what level is X ? if I=0.2A (2.6volt=I*12ohm) then x=3*0.8(datasheet)=2.4volt
am i totaly wrong ??
I'm on the train on my way home. Will have a look when I have this up on a computer screen (rather than a smartphone) and have a schematic to hand :mrgreen:

Mark

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Re: Beeb Resurrection - 2nd scope attempt!

Post by duikkie » Thu Mar 20, 2014 4:07 pm

how can this be true ?

pin 12 and pin 11 of IC 40 give me just about the same signal on the working and non working machines
About 2.3Volt at period of about 65nsec (15.5mhz?)

and

IC42

pin 2, 2volt 65ns ... 1.8volt 65ns

the diffents is 0.5 volt they are connected ?

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Re: Beeb Resurrection - 2nd scope attempt!

Post by duikkie » Thu Mar 20, 2014 4:56 pm

i still thinging that something is wrong with the 8 mhz line. it is dangerly low and the valley to peak maybe 2.3 volt but the scholder behind the peak it also above the 1.3 volt ( tickerpoint ??)

the big qeustion is do become the big sholder came from ic6 itself or are other chips broken ??

ic30? ic37? ic86? ic81

if someone thinks i am wrong please jump in :)

i don't like soldering out chip's if not 1000% right to be broken

so we can bend pin 7 out of ic 6 and measure if there is a big sholder ?
we can break s27 link on the other side of the board ?

someone better idea ?

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Re: Beeb Resurrection - 2nd scope attempt!

Post by 1024MAK » Thu Mar 20, 2014 9:30 pm

duikkie wrote:maybe someone can explane the circuit around pin8 and pin 15 of ic 6

d16,d17,d18 is it 3*0.65 volt=1.95 volt or is it more or less ??
I=0.2 A ??

3 * 0.8=2.4volt (datasheet 1n4002)
duikkie wrote:mark what do you think about the d16,d17,d18 and r114 circuit ?
what level is X ? if I=0.2A (2.6volt=I*12ohm) then x=3*0.8(datasheet)=2.4volt
am i totaly wrong ??
The Ferranti ULA internal logic circuit operate at between 0.84V and 5V depending on the cell type used inside. For example, the ULA used in the ZX Spectrum (a CML type) operates the internal CML cell logic at between 0.84V and 0.95V via internal regulator circuits.
The interface ("peripheral") cells that connect the internal logic cells with the outside world do however normally require +5V so that the outputs are "TTL" compatible.
The first ULA used for the video processor had a problem and ran hot. I believe the resistor (R114) and the diodes are used to supply the internal voltage regulator "bus" that in turn feeds the internal logic (this needs to be 1.3V or greater). I presume this was done to help reduce the heat level in the chip.

In an issue 7, R114 is specified as 18 Ohms.

The exact level at point 'X', the junction between the top of the three diodes, the video processor ULA and R114 does not matter too much, as the video processor ULA has internal voltage regulator circuits. I would expect a voltage here of between 1.95V and 2.4V. In my issue 7 Beeb I measure 2.33V (which uses a VTI VC2069 and is NOT a Ferranti ULA, so the voltage may be different if one of the other chips is in use).

Mark

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Re: Beeb Resurrection - 2nd scope attempt!

Post by 1024MAK » Thu Mar 20, 2014 9:48 pm

1395325150164 with comments.jpg
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Re: Beeb Resurrection - 2nd scope attempt!

Post by 1024MAK » Thu Mar 20, 2014 10:16 pm

I agree that the voltages and waveforms on the various 16 MHz and 8 MHz lines do not look good. However, as Lee is new to using a 'scope, and is using a X1 probe, the results he gives may be misleading.

Lee, a 'scope cable and probe add capacitance to the circuit. At high frequencies or where you are attempting to measure sharp edged square waves with fast rise or fall times, the added capacitance may result in distorted waveforms shown on the 'scope.

That's why I normally use a 'scope probe with a X10 switch, and use it in the X10 position. This effectively compensates for the extra capacitance as long as you calibrate the 'scope probe.

On most 'scopes, there is a test output that outputs a square wave. Hold the probe on this test point, then carefully adjust the trimmer for the best square waveform :wink:

As to the signals, the lower frequency clock signals all look okay. So I am not worried yet that this is a clock signal fault. Lee, what are the data lines D0 to D7 and address lines A8 to A15 doing :?:
What display do you have :?:
I take it you have already swapped the Video Processor for the exact same type / or have tested it in a known working machine :?:

Mark

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Re: Beeb Resurrection - 2nd scope attempt!

Post by duikkie » Fri Mar 21, 2014 7:00 am

asuming the sholder of signal 8 mhz is nasty reading ( i think not , because the shoulder on 16 mhzline is smaller) . we can look if it does it work when coming down.
we know signal on pin 25 ic7 is good, thus 16mhz input does it's work.

to check the 8 mhz line

measure :

pin 4 and 6 ic38 this must be good signal (top-bottom around 5 volt)
pin 12 ic 29 good signal ?
pin 6 ic 44
pin 6 and pin 4 ic 86
pin 4 ic 81

did i forgot a 8 mhz line ??

1024MAK wrote:I agree that the voltages and waveforms on the various 16 MHz and 8 MHz lines do not look good. However, as Lee is new to using a 'scope, and is using a X1 probe, the results he gives may be misleading.

Lee, a 'scope cable and probe add capacitance to the circuit. At high frequencies or where you are attempting to measure sharp edged square waves with fast rise or fall times, the added capacitance may result in distorted waveforms shown on the 'scope.

That's why I normally use a 'scope probe with a X10 switch, and use it in the X10 position. This effectively compensates for the extra capacitance as long as you calibrate the 'scope probe.

On most 'scopes, there is a test output that outputs a square wave. Hold the probe on this test point, then carefully adjust the trimmer for the best square waveform :wink:

As to the signals, the lower frequency clock signals all look okay. So I am not worried yet that this is a clock signal fault. Lee, what are the data lines D0 to D7 and address lines A8 to A15 doing :?:
What display do you have :?:
I take it you have already swapped the Video Processor for the exact same type / or have tested it in a known working machine :?:

Mark

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Re: Beeb Resurrection - 2nd scope attempt!

Post by duikkie » Fri Mar 21, 2014 8:19 am

question to all :)

do you in uk tolk about leading edge , shoulder(with u :)), mountains valley spikes ??

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Re: Beeb Resurrection - 2nd scope attempt!

Post by leenew » Fri Mar 21, 2014 2:55 pm

Hello!
I got drunk by accident last night and I have just woken up :lol:
I think I enjoyed myself?
Now, if my eyes will allow me, I will attempt to catch up on what I have missed.
First of all Mark, I will set up the scope as you say for all future measurements.

George.h - No - I don't know *anything* :D when I say I am new to this I really mean it.
I think I need to get a decent X10 probe on order, so I shall do that this afternoon.
Any recommendations? are they all the same? should I avoid the cheap hong kong stuff?

OK I am off to set the scope up... (Oh, yes it is a Tektronik 7603 beast :D )

Lee.

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Re: Beeb Resurrection - 2nd scope attempt!

Post by leenew » Fri Mar 21, 2014 3:36 pm

Seeing as I am still a bit confused, are all the buttons where they should be?
20140321_152522.jpg
20140321_152604.jpg
20140321_152701.jpg
20140321_152715.jpg
20140321_152748.jpg
Out of interest, what's the middle 7a22 rack for? :D

Lee.

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Re: Beeb Resurrection - 2nd scope attempt!

Post by duikkie » Fri Mar 21, 2014 3:46 pm

how is it possible one picture the right way up =D>
you are learning :)
leenew wrote:Seeing as I am still a bit confused, are all the buttons where they should be?
20140321_152522.jpg
20140321_152604.jpg
20140321_152701.jpg
20140321_152715.jpg
20140321_152748.jpg
Out of interest, what's the middle rack for? :D

Lee.

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Re: Beeb Resurrection - 2nd scope attempt!

Post by duikkie » Fri Mar 21, 2014 3:55 pm

why ch. on 2 volt ?? keep it the same

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Re: Beeb Resurrection - 2nd scope attempt!

Post by duikkie » Fri Mar 21, 2014 4:00 pm

i do find your scopes very modern , at home i have one showed in picture

picture
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Re: Beeb Resurrection - 2nd scope attempt!

Post by leenew » Fri Mar 21, 2014 4:40 pm

I have put channel 2 on 1V

re-measured IC40 pins 11 and 12 to be 2.2v on working beeb and 1.7v on non working beeb
This is the same for IC42 pin 2

IC38 working then non working beeb
pin 4, 5 volt (4.4 volt above ground) - 5.5 volt (5 volt above ground) (signal is more 'wonky'??)
pin 6, just over 3V and on non working beeb 5.5 volt with 5v above ground

IC29
pin 12, good signal on both beebs

IC44
pin 6, 4.8v with 4v above ground on both beebs

IC86
pin 4, good signal 500ns period
pin 6, good signal 2000ns period
IC81
pin 4 good signal 500ns period

IC6
pin 17
pin 18 (D1) only just over 2v from the non working beeb on this pin. all others have 5v busy signals
pin 19
pin 20
pin 21
pin 22
pin 23

A8 to A15 (pins 25 24 23 22 20 19 18 17 of 6502):
working beeb has busy signals all sat around 3v

non working beeb has next to nothing on 17,18,19 and 23
with over 3v on the others.
Oh and there is absolutely nothing on screen - just the loooooooooooong beeeeeeeeeeeeeeep

thanks.

Lee.

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Re: Beeb Resurrection - 2nd scope attempt!

Post by 1024MAK » Fri Mar 21, 2014 5:07 pm

leenew wrote:Seeing as I am still a bit confused, are all the buttons where they should be?
leenew wrote:Out of interest, what's the middle 7a22 rack for? :D
Yes, looking at the pictures, all the important controls appear to be set to reasonable values.

Rack 7a22 is a differential amplifier and by the looks of it, it includes low pass and high pass selectable filters.

Normal inputs measure the input voltage with respect to ground. On mains powered 'scopes, ground (the outer connection on the BNC sockets) is internally connected to both the case, and to the earth connection in the mains lead.

This is not a problem if the equipment you are working on is also earthed, or is earth free and double insulated and this equipment uses an isolating transformer, or is only battery powered.

However, some mains powered equipment operates with voltages that are not referenced to ground (so called live chassis televisions for example). In this case, you cannot connect a normal 'scope input (as you will then try to ground the circuit you are connecting to, and either cause a shock hazard, or short circuit part of the circuitry). Some double insulated mains powered items also are effectively in this class.

So you have to either use a differential adaptor between the 'scope and the equipment you want to test, use a 'scope with a differential amplifier, or use a large isolating transformer to power the equipment you want to test.

Mark

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Re: Beeb Resurrection - 2nd scope attempt!

Post by duikkie » Fri Mar 21, 2014 8:22 pm

can someone please explain why a signal of 1.7volt can work a 74s00 if in datasheet it tells me it must be 2.0 volt min ?? or is 1.5 volt the point ?

i hope your pin 6 on ic38 is a wave form not a line of 3 or 5.5 volt ?

can you switch ic40 or also soldered in ??

----------------------------------------------------------------------
re-measured IC40 pins 11 and 12 to be 2.2v on working beeb and 1.7v on non working beeb
This is the same for IC42 pin 2

IC38 working then non working beeb
pin 4, 5 volt (4.4 volt above ground) - 5.5 volt (5 volt above ground) (signal is more 'wonky'??)
pin 6, just over 3V and on non working beeb 5.5 volt with 5v above ground

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Re: Beeb Resurrection - 2nd scope attempt!

Post by leenew » Sat Mar 22, 2014 10:17 am

Hi Duikkie,
I think my ignorance may be showing here.
When I set the score up as Mark suggested, on I 40 pin12 to the top is 3 volts from ground.
1395483262640.jpg
This is the non working beeb
1395484468034.jpg
Sorry!! :oops:
this is IC38 pin6 working.
1395483358423.jpg
and non working
1395484536486.jpg

all these chips are soldered in but I can swap any if you need me to.

Lee.

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Re: Beeb Resurrection - 2nd scope attempt!

Post by duikkie » Sat Mar 22, 2014 11:04 am

no swaping and soldering yet !! it looks like allthough low voltage the chips gets what they need to work. if they did not it was flat line somewhere. or strange peaks not a little bumb or shoulder. if something is wrong you will see it.
so is flat line most of the time no good. or a realy sharp peak on a waveform.

i think we can skip that the error is in the mhz lines( we have so far i can rember every where a hart beat ;))

did you swap the ic1 yet, i can't rember . ?
maybe this is stupid but did you try another OS rom, i don't think it is hard to break the os rom but you never know.

also i think we have to remove as much's ic's as we can. (YES WE CAN ;))
i think you only need a clock, 6502,OSrom and ram to get a machine going , you need somethingto see or hear. spkr or monitor.

it's a hard one to reapear so far , RAM is next to check.

leenew wrote:Hi Duikkie,
I think my ignorance may be showing here.
When I set the score up as Mark suggested, on I 40 pin12 to the top is 3 volts from ground.
1395483262640.jpg
This is the non working beeb
1395484468034.jpg
Sorry!! :oops:
this is IC38 pin6 working.
1395483358423.jpg
and non working
1395484536486.jpg

all these chips are soldered in but I can swap any if you need me to.

Lee.

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Re: Beeb Resurrection - 2nd scope attempt!

Post by leenew » Sat Mar 22, 2014 11:39 am

Swapped the OS ROM. No change.
Also IC1 is from a good machine.
It does not boot with S25 North or South or off.
Lee.

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Re: Beeb Resurrection - 2nd scope attempt!

Post by duikkie » Sat Mar 22, 2014 2:53 pm

there is every where the nomal 5 volt on the chips and the ground ?

i don't no yet where to look for today everything seems it is oke but somewhere is not.

you can check ic45 for strange things.
also ic8 to ic13
all ram related

else we must rest this one a little time , maybe an other day
we have some idea's :idea: :idea: :idea:

leenew wrote:Swapped the OS ROM. No change.
Also IC1 is from a good machine.
It does not boot with S25 North or South or off.
Lee.

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Re: Beeb Resurrection - 2nd scope attempt!

Post by leenew » Sat Mar 22, 2014 4:46 pm

Hi,
I have had another quick look at this.
IC45 seems OK.

I am having trouble with IC8 to 13.
I have had a look at IC8 on the working beeb and IC8 on the non working beeb and there are many differences in the signal, but I am not sure if this is because the fault is located there, or whether the memory is not being addressed on the non-working machine as it has not managed to boot?
I don't have any spares of these IC's either :?
This one is becoming a bit of a pain :D

Lee.

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Re: Beeb Resurrection - 2nd scope attempt!

Post by 1024MAK » Sat Mar 22, 2014 11:26 pm

leenew wrote:I am having trouble with IC8 to 13.
I have had a look at IC8 on the working beeb and IC8 on the non working beeb and there are many differences in the signal, but I am not sure if this is because the fault is located there, or whether the memory is not being addressed on the non-working machine as it has not managed to boot?
I don't have any spares of these IC's either :?
This one is becoming a bit of a pain :D
Not all repairs are quick and easy :lol:
Because the CPU's are attempting to execute different code (who the hell knows what the "bad broken" Beeb CPU is doing), you will get different results when comparing a working machine with a faulty machine.
The most important thing, is to test to see if there are any "stuck" address, control or data lines. That is any that are always 0V, always +5V or stuck at a static level somewhere in-between. It is also useful if you report any waveform that is distorted (not within normal "TTL" logic levels, see here: Logic signal voltage levels).

Mark

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Re: Beeb Resurrection - 2nd scope attempt!

Post by 1024MAK » Sat Mar 22, 2014 11:28 pm


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Re: Beeb Resurrection - 2nd scope attempt!

Post by CMcDougall » Sat Mar 22, 2014 11:32 pm

lee wrote:This one is becoming a bit of a pain
have you tried it in the dish washer?? :lol:
i just put my :evil: very :evil: naughty Issue7 in for a wash, after taking the socketed chips /jumpers off. Will let you know how it gets on in a week after drying :-k
ImageImageImage

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Re: Beeb Resurrection - 2nd scope attempt!

Post by duikkie » Sat Mar 22, 2014 11:33 pm

i am thinking out of the box [-X

but maybe we do need two patients , one how will borrow some organs for a ill one

how to link up two beebs on one 5volt,-5volt, gnd unit not sure yet but then

take out chips from the non working beeb like ic6 (the heart), fitting the non working beeb with lines from the working beeb. open heart tranplantation :)

so allso with the brain , the memory (ram) :shock:

the frankestein methode ???

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Re: Beeb Resurrection - 2nd scope attempt!

Post by 1024MAK » Sat Mar 22, 2014 11:39 pm

The 6502 CPU:
leenew wrote:Oh and there is absolutely nothing on screen - just the loooooooooooong beeeeeeeeeeeeeeep
Lee, as the 6502 CPU is not managing to read the ROM code, it is not setting up the correct data in to the display controller chip, nor is the CPU setting up the sound chip. Hence no display and the sound chip going beeeeeeeeeeeeeeep...
leenew wrote:A8 to A15 (pins 25 24 23 22 20 19 18 17 of 6502):
working beeb has busy signals all sat around 3v
Do you mean these signals are cycling (toggling between logic high and logic low)? Or are you saying something else?
leenew wrote:non working beeb has next to nothing on 17,18,19 and 23
Do you mean these pins are all logic low (between 0V and 0.5V)?
leenew wrote:with over 3v on the others.
Again, explain please?

Mark

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Re: Beeb Resurrection - 2nd scope attempt!

Post by 1024MAK » Sat Mar 22, 2014 11:50 pm

leenew wrote:IC6
pin 17
pin 18 (D1) only just over 2v from the non working beeb on this pin. all others have 5v busy signals
pin 19
pin 20
pin 21
pin 22
pin 23
What about D7, pin 24?

I am not keen on the signal on D1, pin 18. Can you post a picture of the signal on the 'scope please :wink:

Do you get the same on the 6502 CPU pins 33 to 26 ?

It is possible for a faulty DRAM chip to drag a data line down.

Also, have you swapped IC14 (74LS245) between a working Beeb and your non-working Beeb? If yes, and is has / had no effect, try removing it on your non-working Beeb (that's right, leave it out). Then do the 'scope checks on BOTH 6502 CPU pins 33 to 26 AND IC6 pins 17 to 24 please.

I'm off to bed now, I have to get up early to go to work in the morning :(

Mark

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Re: Beeb Resurrection - 2nd scope attempt!

Post by leenew » Sun Mar 23, 2014 10:11 pm

Hi Mark,
Sorry for my incompetence! :mrgreen:

let's try again:

Pin 25 6502 of the working Beeb looks like this ...
1395612959066.jpg




Whilst on the non working one it looks like this ....
1395613059515.jpg


The none working Beeb has next to nothing Eg Logic Low just over 0 volts on pin 18,19, and 23 of the 6502

IC6 Pin 24 looks like this on the working Beeb....
1395613335939.jpg


and similar on the non working Beeb...



This is the picture of Pin 18 IC6 of the working Beeb....
1395613335939.jpg



Pins 33 to 26 look similar on both machines.

With the 245 out pins 33 to 26 of the 6502 out have decent cycling signals, IC6 pins 17 to 24 all have strong signals except for pin 18 which only has under 2.5 volts on it.

Pin 18 IC6 looks very bad to my incompetent eyes :shock:



Thanks

Lee
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Re: Beeb Resurrection - 2nd scope attempt!

Post by nOmArch » Sun Mar 23, 2014 10:46 pm

Didn't Mark have a couple of those swanky Beeb diagnostics boards that Acorn themselves used for sale?

Might be worth giving him a shout.
Alex

Back up to 1 Beeb again. \o/

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Re: Beeb Resurrection - 2nd scope attempt!

Post by leenew » Sun Mar 23, 2014 11:01 pm

Hi Alex,
Yes, I think I remember that being mentioned.
Having thought about it for the last 2 minutes though, I think I wanna do this the hard way :lol: (well is not that hard - I post some pics and Mark tells me what to do next :D

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