Quick measurement
Quick measurement
I'm on holiday and away from my Beeb stuff so if anyone has a Model B and a DMM handy and could do a quick couple of measurements for me, I would be most grateful. It's just two power-off passive resistance checks on the analogue (joystick) connector, between the the two fire button inputs and the +5v line. So, as illustrated below, from I0 Pin 13 to +5v Pin 1 and from I1 Pin 10 to +5v Pin 1. It would be useful to measure each twice with the meter leads reversed so four measurements in total please. That's it and thanks!
-
- Posts: 191
- Joined: Fri Apr 13, 2018 1:48 pm
- Contact:
Re: Quick measurement
Might be able to do this, if my multimeter probes will fit into the sockets ... Stupid newbie question, but that diagram is as if you're looking at the analogue socket from outside the case not inside, yes?
Re: Quick measurement
Yes, and I think Pin 1 is top right but there are also probably little moulded numbers in the plastic. A straightened paper clip might fit the sockets....?
( For orders of magnitude btw, I'm thinking about 900 ohms ? )
.
( For orders of magnitude btw, I'm thinking about 900 ohms ? )
.
Last edited by MartinB on Sat Aug 11, 2018 9:36 pm, edited 1 time in total.
-
- Posts: 191
- Joined: Fri Apr 13, 2018 1:48 pm
- Contact:
Re: Quick measurement
Ok, I've been trying with solder wire but can't get a good connection. Give me a few hours and I'll take the lid off and get to the connections from the inside.
Re: Quick measurement
Please don't go to any trouble, it's certainly not urgent - I was just trying to settle a collection of project thoughts in my head. Anytime in the next few days will be fine... 

Re: Quick measurement
Do you have some reason to believe it won't be ~10K
Re: Quick measurement
Yes, because of the 6522 having what I believe from previous testing to be an internal ~1k pull-up to 5v on the data lines. It's just something that I would check on a few Beebs if I was at home but being away, the thought is niggling me. If it is as I suspect, then the 10k's have actually reduced the overall I0/I1 pull-up resistance to ~900 ohms. No crisis, just interest and relevant to my other projects.
.
.
Last edited by MartinB on Sat Aug 11, 2018 10:06 pm, edited 2 times in total.
-
- Posts: 191
- Joined: Fri Apr 13, 2018 1:48 pm
- Contact:
Re: Quick measurement
DISCLAIMER: I know very little about electronics (I'm having flashbacks to A-level physics!) and I only bought my multimeter so I could check I'd recapped my PSUs properly. That being said, I *think* my approach of finding some wires, jamming one end into the socket and pressing the multimeter probe against the other end works!
I0 Pin 13 to +5v pin 1:
Black probe(COM) of MMD to pin 1, red probe to pin 13: 1.077 kOhm.
Red probe of MMD to pin 1, black to pin 13: 1.06 kOhm.
I1 pin 10 to +5v pin 1:
Black to pin 1, red to pin 10: 1.08 kOhm.
Red to pin 1, black to pin 10: 1.062 kOhm.
So looks like for both pairs it's approximately 1.08 kOhm in one direction and 1.06 kOhm in the other.
I0 Pin 13 to +5v pin 1:
Black probe(COM) of MMD to pin 1, red probe to pin 13: 1.077 kOhm.
Red probe of MMD to pin 1, black to pin 13: 1.06 kOhm.
I1 pin 10 to +5v pin 1:
Black to pin 1, red to pin 10: 1.08 kOhm.
Red to pin 1, black to pin 10: 1.062 kOhm.
So looks like for both pairs it's approximately 1.08 kOhm in one direction and 1.06 kOhm in the other.
Re: Quick measurement
That’s brilliant, thanks Adrian...
So your 6522 has internal pull-ups of roughly 1.2k ohms which is what I think I originally measured on some of mine.
Thanks again
(Any other samples would be interesting if anyone has a bored moment to spare....
)


So your 6522 has internal pull-ups of roughly 1.2k ohms which is what I think I originally measured on some of mine.
Thanks again

(Any other samples would be interesting if anyone has a bored moment to spare....

Re: Quick measurement
As I had a DB15 to hand, I just had a quick check of my "to hand" machines and the issue 3 has the same reading as above, while the issue 7 and master both have 0.96x kOhms in both directions.
Caveat, my battery is low in my meter!
Caveat, my battery is low in my meter!
Re: Quick measurement
Issue 4 Beeb
1.074 (10) & 1.071 (13) in K
1.074 (10) & 1.071 (13) in K
Last edited by Elminster on Sun Aug 12, 2018 10:22 am, edited 1 time in total.
-
- Posts: 191
- Joined: Fri Apr 13, 2018 1:48 pm
- Contact:
Re: Quick measurement
I should have mentioned that mine is an issue 7.
Re: Quick measurement
Thanks also Richard and Duncan, that’s great...

I’ll explain in due course....


I’ll explain in due course....

- 1024MAK
- Posts: 8285
- Joined: Mon Apr 18, 2011 4:46 pm
- Location: Looking forward to summer in Somerset, UK...
- Contact:
Re: Quick measurement
Martin, some more data for you...
Everyone above, you did know that the test is only valid if you are using the correct coloured test leads, don't you?
Mark

Code: Select all
DT-4000ZC Fluke DT-4000ZC Fluke
Computer Board Serial number Pin 10 Pin 10 Pin 10 Pin 10 Pin 13 Pin 13 Pin 13 Pin 13
issue normal rev. normal rev. normal rev. normal rev.
BBC B ??? 01-ANB04-6011871 1.140k 1.193k 1.146k 1.189k 1.121k 1.170k 1.125k 1.167k
BBC B 7 03-ANB01-3088426 980R 1.002k 983R 1.001k 992R 1.013k 994R 1.012k
BBC B+ 64K 01-ANB51-3504713 856R 871R 859R 870R 856R 870R 858R 870R
BBC B 7 01-ANB01-3023119 957R 974R 970R 974R 958R 975R 961R 975R
Master 128 2 10k 10k 10k 10k 10k 10k 10k 10k
Electron with Plus 1 2.182k 2.183k 2.184k 2.186k 2.177k 2.178k 2.179k 2.181k
The Beeb where the board issue is shown as ??? may be an issue 4 or an issue 7 (I think).

Last edited by 1024MAK on Sun Aug 12, 2018 10:51 pm, edited 1 time in total.
Reason: Amended so that it is clear that one of the computers tested is a B+
Reason: Amended so that it is clear that one of the computers tested is a B+
For a "Complete BBC Games Archive" visit www.bbcmicro.co.uk NOW!
BeebWiki - for answers to many questions...
Logic Levels for 5V TTL Systems
Fault finding index
BeebWiki - for answers to many questions...
Logic Levels for 5V TTL Systems
Fault finding index
Re: Quick measurement
Wow! 
Thanks Mark! I’ll have a digest and comment later....

Thanks Mark! I’ll have a digest and comment later....

Re: Quick measurement
Perhaps we should synchronise multimeters.
Mine is an evtech 330.
I have a Maplin gold somewhere but I don’t think I need to confirm my results
Mine is an evtech 330.
I have a Maplin gold somewhere but I don’t think I need to confirm my results

Re: Quick measurement
Mark - first off, I also have the excellent DT-4000 and a Fluke (the respected Model 12) and the two always read close enough for the delta not to matter.
All the Beebs look as I would expect, we’re just seeing the tolerance of the external 10k pull-ups working in parallel with the 6522 internal pull-up. The Elk doesn’t use a 6522, the joystick fire buttons are connected to discrete logic gates so we’re simply seeing the 2K2 pull-ups. The Master though does puzzle me... it’s schematic is identical to the Beeb but it’s as if the 6522 in yours doesn’t have internal pull-ups.....

All the Beebs look as I would expect, we’re just seeing the tolerance of the external 10k pull-ups working in parallel with the 6522 internal pull-up. The Elk doesn’t use a 6522, the joystick fire buttons are connected to discrete logic gates so we’re simply seeing the 2K2 pull-ups. The Master though does puzzle me... it’s schematic is identical to the Beeb but it’s as if the 6522 in yours doesn’t have internal pull-ups.....


- 1024MAK
- Posts: 8285
- Joined: Mon Apr 18, 2011 4:46 pm
- Location: Looking forward to summer in Somerset, UK...
- Contact:
Re: Quick measurement
I tested the Master 128 and the Plus 1 out of curiosity. I was not surprised by the results for the Plus 1, but was by the results on that Master.
I have some other Masters that I can test later.
Mark
I have some other Masters that I can test later.
Mark
For a "Complete BBC Games Archive" visit www.bbcmicro.co.uk NOW!
BeebWiki - for answers to many questions...
Logic Levels for 5V TTL Systems
Fault finding index
BeebWiki - for answers to many questions...
Logic Levels for 5V TTL Systems
Fault finding index
Re: Quick measurement
Ok, thanks Mark. Maybe you’ve previously robbed the 6522 from that Master for another fix because it’s almost as if it doesn’t have one fitted! 

Re: Quick measurement
A dead 6522? I will see if I get 5 mins tomorrow to test a master as well.
- 1024MAK
- Posts: 8285
- Joined: Mon Apr 18, 2011 4:46 pm
- Location: Looking forward to summer in Somerset, UK...
- Contact:
Re: Quick measurement
Hah ha! You should know that pinching bits from a Master 128 is most likely too much like hard work, as in most Masters, everything except the ROMs are soldered in... (and I'm too lazy to go to that much effort when I have some Beebs to borrow bits from).
No, to the best of my knowledge, the Master 128 that I tested and give results for, is fully operational (it's also the only Master that currently has a memory/RTC/CMOS back-up battery fitted...).
So, anyway, I tested two other Masters, taking into account resistor tolerances, they all read the same - that is 10k.
So I investigated the first Master 128. Photo here of IC8:- (G65SC22P-2 in position IC8 in a Master)
So that looks like a CMOS type. Presumably then, it does not have an internal pull-up resistance.
Mark
For a "Complete BBC Games Archive" visit www.bbcmicro.co.uk NOW!
BeebWiki - for answers to many questions...
Logic Levels for 5V TTL Systems
Fault finding index
BeebWiki - for answers to many questions...
Logic Levels for 5V TTL Systems
Fault finding index
- 1024MAK
- Posts: 8285
- Joined: Mon Apr 18, 2011 4:46 pm
- Location: Looking forward to summer in Somerset, UK...
- Contact:
Re: Quick measurement
For a "Complete BBC Games Archive" visit www.bbcmicro.co.uk NOW!
BeebWiki - for answers to many questions...
Logic Levels for 5V TTL Systems
Fault finding index
BeebWiki - for answers to many questions...
Logic Levels for 5V TTL Systems
Fault finding index
Re: Quick measurement
So, should we swap the meter end or the clip end when checking the reverse or both

EDIT: Sorry, OT.
PS Is it only issue 7 beebs that have the support in the middle of the vent slot?
Last edited by tricky on Sun Aug 12, 2018 9:43 pm, edited 2 times in total.
Re: Quick measurement
My issue 4 has no support, my b+ does. Issues 7s not to hand.
Results for a b+
13 - 1.275k
10 - 1.278k
Will dig masters out tomorrow
- 1024MAK
- Posts: 8285
- Joined: Mon Apr 18, 2011 4:46 pm
- Location: Looking forward to summer in Somerset, UK...
- Contact:
Re: Quick measurement
Mark
For a "Complete BBC Games Archive" visit www.bbcmicro.co.uk NOW!
BeebWiki - for answers to many questions...
Logic Levels for 5V TTL Systems
Fault finding index
BeebWiki - for answers to many questions...
Logic Levels for 5V TTL Systems
Fault finding index
Re: Quick measurement
Someone stole the squiggle snake in the cmos one
Re: Quick measurement
Don't be silly Duncan, it's not a squiggle snake, it's clearly a spring....
Thanks again Mark, that of course answers the Master query. The higher effective value isn't actually going to be a problem but it is valuable information for me to be aware of.
No need for any more testing then folks, I have the full story now and minor variations are not significant.
Thanks again all


Thanks again Mark, that of course answers the Master query. The higher effective value isn't actually going to be a problem but it is valuable information for me to be aware of.
No need for any more testing then folks, I have the full story now and minor variations are not significant.
Thanks again all


Re: Quick measurement
BBC Model B 32k issue 7, Sidewise ROM board with 16K RAM
Archimedes 420/1 upgraded to 4MB RAM (mid- restoration)
Acorn System 1 home-made replica
Archimedes 420/1 upgraded to 4MB RAM (mid- restoration)
Acorn System 1 home-made replica
Re: Quick measurement
Heh heh 
