Problems booting beeb issue 4

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DaveLecky
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Re: Problems booting beeb issue 4

Post by DaveLecky » Sat Sep 28, 2019 5:01 pm

Hi 1024MAK,

I know what you are saying, but I can’t justify the cost of test equipment for a one off use.

I appreciate the help I have received from the forum members but being retired I have to watch what I spend in my hobbies.

Dave
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Re: Problems booting beeb issue 4

Post by 1024MAK » Sat Sep 28, 2019 5:54 pm

Before the travel industry started imploding, in 2016 I took an internal flight from the local regional airport near me (Bristol) to Aberdeen for a retro computer meet-up (not an Acorn event mind). After comparing costs and travel times, I found the flight the most suitable for me. In fact, this journey took less time (well, for the outward trip) than me driving to Cambridge earlier this month for that ABug meet-up.

At the last ABug we had two members from overseas. So in my opinion ‘near’ is a relative term.

Although I fully understand that such journeys and the hotel costs may not be affordable for everyone.

Mark
Last edited by 1024MAK on Sat Sep 28, 2019 5:57 pm, edited 1 time in total.

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Re: Problems booting beeb issue 4

Post by 1024MAK » Sat Sep 28, 2019 6:05 pm

DaveLecky wrote:
Sat Sep 28, 2019 5:01 pm
Hi 1024MAK,

I know what you are saying, but I can’t justify the cost of test equipment for a one off use.

I appreciate the help I have received from the forum members but being retired I have to watch what I spend in my hobbies.

Dave
Logic probes are less than £15. I have just spotted this kit on eBay. Definitely worth a look for £3.99. See also the suppliers web site https://www.mitchelectronics.co.uk/product/logic-probe/

Mark
Last edited by 1024MAK on Sat Sep 28, 2019 6:11 pm, edited 1 time in total.

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Re: Problems booting beeb issue 4

Post by Elminster » Sat Sep 28, 2019 6:09 pm

I flown Glasgow <-> stansted a couple of times. Price is okay if you time it right, but usually mid week as work related. Cost less than driving it. Not that I paid as I expensed it.
Last edited by Elminster on Sat Sep 28, 2019 6:09 pm, edited 1 time in total.

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Re: Problems booting beeb issue 4

Post by Kazzie » Sat Sep 28, 2019 8:55 pm

I've gone at it to try to recreate your mode 0 screen on my machine. I set S25 south (for a 16k machine), poked 128 into &028E (to fool the OS that it had 32k connected) and switched to mode 0. Here's a quick photo:
IMG_20190928_1941109.jpg
And here's your mode 0 photo from earlier for easy reference:
Image

Mode 0 displays 20k of RAM as screen memory, which would normally be &3000-&7FFF, but we've only got 16k available in these machines, so the first six and a half lines are a repeat of what's at the bottom of the screen (we see &3000-&3FFF, then &0000-&3FFFF). On my screen, it's possible to see the line-and-two-thirds of vertical bars (and some black area) is repeated at the top of the screen. In your machine, the repetition isn't as obvious to see as both areas happen to be completely black.

From six-and-a-half lines down until the end of the screen, we see a graphical interpretation of the 16k of RAM that's currently available to the machines. The contents of both machines' RAM look similar at the start: a few partially filled characters, then a solid white block of a few characters, some more partially filled characters, then the end of line 7 and the start of line 8 both have the same "wavy lines". (Really technical terminology here! :P ) This low RAM is used for zero-page variables and the CPU's stack, so it's reasonable that they look similar, as both machines have succeeded in booting. (Disclaimer: my machine had DNFS and other ROMs fitted, I don't know if yours did when the photo was taken.)

A big difference in your RAM's display is that this visual pattern for the lower RAM is repeated roughly half-way down the rest of the screen. This implies to me that as far as your video circuitry is concerned, the contents of memory &0000-&1FFFF is the same as &2000-&3FFFF. Or at least the bottom parts of them. (There's no such repetition in your photo of a crashed Mode 6 display; mode 6 only uses 8k of display RAM, or &2000-3FFF on a 16k machine.)

On the above evidence, I suspect that there's something funny going on with address line A13, which is used to distinguish between (e.g.) &0000 and &2000.

Address line A13 is buffered by IC13 (81ls95), and on the other side it is connected to RAM address line A6 (I'll call it RA6) on all the RAM chips, as are the other buffer chips IC8 to IC12. A fault on IC13 could result in it's output for RA6 being unreliable. Alternatively, a fault on one of the other chips could pull RA6 high or low, working against IC13. If the resulting voltage is in the "undefined" middle region, unreliable things could happen.

I'm trying to work out logically in my head how a fault on one of these buffers could cause all the faults we see (CPU sometimes unable to tell when it's already erased RAM, memory locations &2000 away from each other read as having the same contents when displayed on the screen) but I haven't managed to come to a conclusive answer yet. That's not to say there won't be one forthcoming: my brain's slowing down a bit this evening having been up since 5am. (Toddlers don't know the meaning of a weekend lie-in!)

:arrow: tl;dr; Don't give up on the machine quite yet!

If you get the motivation, a voltage reading on the pins of IC13 might give some useful information about what A13 and RA6 look like compared to the other address lines that are connected to it.
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Re: Problems booting beeb issue 4

Post by DaveLecky » Sun Sep 29, 2019 8:22 am

Hi 1024MAK,

Thanks for the info and advice, I have ordered a logic probe....

Dave
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Re: Problems booting beeb issue 4

Post by DaveLecky » Sun Sep 29, 2019 8:33 am

Hi Kazzie,

I will take the voltage readings later this morning, thanks for the encouragement.

I have ordered a logic probe from eBay, just in case, but won’t arrive until Thursday

Here are some screens displayed with S25 north, repeatedly pressing Break....
4E7B69AC-7A97-4D34-AF4F-FDFB653CCA60.jpeg
BC1089D8-7CF7-4796-93C4-C23E3F6E9C89.jpeg
343B01F8-1E53-49DA-A526-09C0C9907808.jpeg
9942E128-308D-4913-B044-1C5DC3B822E9.jpeg
90B88F99-A55D-4AC6-9CA6-343FFBDAF6AB.jpeg

Dave
Last edited by DaveLecky on Sun Sep 29, 2019 8:36 am, edited 1 time in total.
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Re: Problems booting beeb issue 4

Post by DaveLecky » Sun Sep 29, 2019 10:06 am

Hi Kazzie,

With S25 North, beep bop, keyboard not working.
515CB8B1-15C8-4FA5-84EA-4C6060900493.jpeg
IC 12
1= 3.92 2= 3.52 3= 2.9 4= 3.38 5= 3.01 6= 3.4 7= 3.1 8= 3.2 9= 2.8 10= 0.05

11= 2.8 12= 2.99 13= 2.77 14= 3.38 15= 3.01 16= 3.42 17= 3.64 18= 4.66 19= 3.8 20= 4.68

IC 13
1= 4.2 2= 3.58 3= 3.01 4= 3.57 5= 3.16 6= 3.62 7= 3.2 8= 3.57 9= 2.91 10= 0.04

11= 2.88 12= 3.56 13= 2.87 14= 3.56 15= 3.1 16= 3.57 17= 3.49 18= 3.89 19= 4.2 20= 4.6

Switching on/off sometimes gives... 32k, nothing, once got 33k then after a delay of a few seconds a click of a relay.

Pressing break gives various outputs to screen, some coloured.
073DE69A-CA44-43AA-87BB-ECABC4C00A0D.jpeg
5F4FB0BA-9531-4922-BEBA-314D6985FF20.jpeg
45DC9D1F-C47E-4A7B-9D76-6487971935D6.jpeg
1D2E8F7B-4571-4FB8-AF53-9EF0B6A5D97C.jpeg
3B69D2EC-7D4B-42AF-ACE6-45C19E72BA58.jpeg
Dave
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Re: Problems booting beeb issue 4

Post by Kazzie » Sun Sep 29, 2019 3:56 pm

DaveLecky wrote:
Sun Sep 29, 2019 10:06 am
Hi Kazzie,

With S25 North, beep bop, keyboard not working.

515CB8B1-15C8-4FA5-84EA-4C6060900493.jpeg

IC 12
1= 3.92 2= 3.52 3= 2.9 4= 3.38 5= 3.01 6= 3.4 7= 3.1 8= 3.2 9= 2.8 10= 0.05

11= 2.8 12= 2.99 13= 2.77 14= 3.38 15= 3.01 16= 3.42 17= 3.64 18= 4.66 19= 3.8 20= 4.68

IC 13
1= 4.2 2= 3.58 3= 3.01 4= 3.57 5= 3.16 6= 3.62 7= 3.2 8= 3.57 9= 2.91 10= 0.04

11= 2.88 12= 3.56 13= 2.87 14= 3.56 15= 3.1 16= 3.57 17= 3.49 18= 3.89 19= 4.2 20= 4.6
That's a lot of good screenshots, thanks. The machine is clearly grumpy with S25 north. But first let's dig through the measurements:

Rearranging your measurements of IC12 and IC13 according to the values they're buffering:

Code: Select all

IC13 pin 18: 3.89      IC13 pin 17: 3.49
A13 (IC13p2): 3.58     RA6 (IC13p3): 3.01
A12 (IC13p4): 3.57     RA5 (IC13p5): 3.16
A11 (IC13p16): 3.57    RA4 (IC13p15): 3.1
A10 (IC13p5): 3.16     RA3 (IC13p7): 3.2
A9 (IC13p14): 3.56     RA2 (IC13p13): 2.87
A8 (IC13p8): 3.57      RA1 (IC13p9): 2.91
A7 (IC13p12): 3.56     RA0 (IC13p11): 2.88
Gate pin 1: 4.2        
Gate pin 19: 4.2       

IC12 pin 18: 4.66      IC12 pin 17: 
A6 (IC12p2): 3.52      RA6 (IC12p3): 2.9
A5 (IC12p4): 3.38      RA5 (IC12p5): 3.01
A4 (IC12p16): 3.42     RA4 (IC12p15): 3.01
A3 (IC12p5): 3.01      RA3 (IC12p7): 3.1
A2 (IC12p14): 3.38     RA2 (IC12p13): 2.77
A1 (IC12p8): 3.2       RA1 (IC12p9): 2.8
A0 (IC12p12): 2.99     RA0 (IC12p11): 2.8
Gate pin 1: 3.92
Gate pin 19: 3.8

There's nothing sticking out like a sore thumb there. Though I suspect that the machine had crashed at this point; the keyboard wasn't working, and 3.5V is where the NMOS 6502 tends to leave it's address lines when it halts. This is one of those places where your logic probe will help give a clearer picture. :)



As for the screen captures you have, there's a lot going on:
  • There are some typical BASIC error messages (Division by zero, Syntax error, Type mismatch, etc) that are either being prompted by some phantom keyboard input, or are being shown by mistake
  • Some BASIC tokens are being printed onscreen; these must have come from the BASIC ROM (which would be at &8000-&BFFF in memory)
  • When trying to read the name of the current language from the ROM, the machine sometimes manages to miss and print parts of the nearby copyright string instead:
BASIC-ROM-hex.png
Screenshot of the start of the BASIC 1.0 ROM in a hex editor
  • Some odd characters of the teletext screen are wrong: e.g. '3/4' shows up in one picture. A regular pattern of these (being 'n' values away from the correct character) can indicate a RAM fault, but there's nothing regular in these. Coloured characters indicate that faulty values in (or coming from) the display RAM include the teletext control codes to change text colour. The background colour can likewise be changed to green by a combination of these commands, see page 152 of the user guide for some examples.
  • As for the screenfull of gingham pattern, I've no idea how your machine made that! :shock:
I've not thrown out a lot of answers there, I know. But writing it all out sometimes helps. And perhaps a different pair of eyes will spot something I didn't.


Given the extent to which the machine is misbehaving, it might be worth trying Tricky's Test OS ROM, which would replace the Acorn MOS ROM in IC51. It's specially written to avoid relying on being able to read and write values in RAM, so should run more reliably. The sequence of patterns it shows on screen, and any problems with them, may be a more reliable yardstick than the smorgasbord of faults we're seeing at the moment. Do you have the ability to burn EPROMs, perchance?
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Re: Problems booting beeb issue 4

Post by DaveLecky » Sun Sep 29, 2019 6:40 pm

Hi Kazzie,

I do have Tricky’s test rom and the service manual rom, given to me by Dave H.

I tried these in a beeb some time ago but couldn’t make any sense out of what I was looking at.

I found a video on YouTube but it didn’t enlighten me at all, so I disregarded them.

I’ll try again online for some instructions.

I take it you can interpret the images ?

Dave
Last edited by DaveLecky on Sun Sep 29, 2019 6:44 pm, edited 1 time in total.
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Re: Problems booting beeb issue 4

Post by Kazzie » Mon Sep 30, 2019 7:41 am

DaveLecky wrote:
Sun Sep 29, 2019 6:40 pm
Hi Kazzie,

I do have Tricky’s test rom and the service manual rom, given to me by Dave H.

I tried these in a beeb some time ago but couldn’t make any sense out of what I was looking at.

I found a video on YouTube but it didn’t enlighten me at all, so I disregarded them.

I’ll try again online for some instructions.

I take it you can interpret the images ?

Dave
There's a stroke of luck!
I made a video of the test ROM running in an emulator, It's uploaded as an attachment to this post. Most of the action is in the first few seconds: the ROM displays an example title screen from Frogger in mode 7, and plays some sounds, then switches to mode 0 (IIRC) to display the contents of the RAM, and flashes through all eight colours. The rest is displaying a series of patterns that can help indicate specific RAM faults. There's also some flashing LEDs on the keyboard, and clicking from the cassette relay, but these obviously aren't included in the emulator video.

On a simplistic level, we want to see how similar or different your images are. If you can take a nice clear video or sequence of pictures, I (or one of several others) can help interpret them. Take note of the presence or absence of activity on the LEDs and cassette relay, if they aren't apparent on a video.
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Re: Problems booting beeb issue 4

Post by DaveLecky » Mon Sep 30, 2019 7:48 am

Thanks Kazzie, I’ll try to do that today.

Dave
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Re: Problems booting beeb issue 4

Post by 1024MAK » Mon Sep 30, 2019 10:05 am

Before you fit the test ROM in the OS socket (IC51), can you please use your multimeter to carry out some tests. Please ensure the computer is switched off before you start. It is best if the ROM is removed from the socket.

Switch your multimeter to the continuity range, or the 200Ω resistance range.

Now test between the following pins:
IC51 pin 1 to IC1 pin 25 (6502 CPU A15)
IC51 pin 1 to IC51 pin 28 (+5V / VCC)
IC51 pin 27 to IC1 pin 24 (6502 CPU A14)
IC51 pin 27 to IC51 pin 28 (+5V / VCC)

Then post the results here.

Thanks

Mark

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Re: Problems booting beeb issue 4

Post by DaveLecky » Mon Sep 30, 2019 11:45 am

Hi 1024MAK,
here are the readings, taken twice to confirm.



IC51 pin 1 to IC1 pin 25 (6502 CPU A15) = 0.4
IC51 pin 1 to IC51 pin 28 (+5V / VCC) = 0. Open circuit
IC51 pin 27 to IC1 pin 24 (6502 CPU A14) = 0.4
IC51 pin 27 to IC51 pin 28 (+5V / VCC) = 0 open circuit

Dave
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Re: Problems booting beeb issue 4

Post by 1024MAK » Mon Sep 30, 2019 1:00 pm

DaveLecky wrote:
Mon Sep 30, 2019 11:45 am
Hi 1024MAK,
here are the readings, taken twice to confirm.

IC51 pin 1 to IC1 pin 25 (6502 CPU A15) = 0.4
IC51 pin 1 to IC51 pin 28 (+5V / VCC) = 0. Open circuit
IC51 pin 27 to IC1 pin 24 (6502 CPU A14) = 0.4
IC51 pin 27 to IC51 pin 28 (+5V / VCC) = 0 open circuit

Dave
These results indicate that the wiring to pins 1 and 27 of the OS ROM socket (IC51) has not been modified since the board was manufactured. So at the moment, this socket is not fully compatible with a EPROM chip.

It is possible that an EPROM may work, but it may not, and that is a pain, as working out what is going on in a machine that is faulty is hard work.

[I have not fully investigated this yet, but what I think happens is that in some EPROMs, as pin 1 is a power input pin, the EPROM may draw power from the CPU address line A15 and exceed the drive current of the relevant CPU pin, dragging the voltage on this line down below the logic high level. The Beebs address decoder circuitry then deselects the ROM...]

There are a number of options:
  1. Use a couple of DIL sockets so that you make an adapter, you can use an EPROM in the top of the stack of sockets. See below.
  2. Bend pin 1 and pin 27 of the EPROM out, so they don’t make contact with the socket, then use some fine wire to link the EPROM pins 1, 27 and 28 together.
  3. Modify the PCB tracks and add suitable wiring to the Beebs PCB so that IC51 socket is compatible with EPROMs. I can show you some pictures taken from a board that was modified (I think) at time of manufacture showing what needs to be done.
DIL sockets adapter
If you choose option 1, please read through all these instructions at least twice before attempting this.

First, put a new stamped pin socket in the main board IC51 socket. Now test (continuity or resistance range again) to make sure that every pin of the top (new) socket is making electrical contact with the relevant pin on the original soldered in socket. If yes, continue.

Now remove the new socket. Then using some suitable fine/narrow long nose pliers, get hold of pin 1 on the socket and push it out of the plastic. Do the same for pin 27. The objective is to provide electrical separation between pin 1 of the main board socket and that of the second socket that you are going to plug the EPROM into. Same reason also applies to pin 27.
Now refit it into the original socket for IC51 on the main board.

Grab another new DIL socket. You will also need some very, very fine copper wire. Use the fine wire to link pins 1, 28 and 27 together. Your solder connections have to be as close as possible to the plastic body of the socket. Now cut off the remainder of pins 1 and 27. Do NOT cut off any other pins. Pin 28 is the +5V/VCC supply pin, and the objective is to feed +5V from pin 28 to both pin 1 and pin 27 of the EPROM that you can then fit into this socket. There is no need to bend the legs of the EPROM.

Now you can fit this socket complete with EPROM into the modified socket you have already fitted in the original IC51 socket. You should now have an EPROM on top of a stack of three sockets! Make sure that they are all firmly pushed together. Now power up ;-)

Mark
Last edited by 1024MAK on Mon Sep 30, 2019 1:21 pm, edited 1 time in total.

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Re: Problems booting beeb issue 4

Post by DaveLecky » Mon Sep 30, 2019 1:10 pm

Hi Kazzie / 1024MAK,

I couldn’t upload the files to the post.....too big.?

Try these links to my Dropbox.....

https://www.dropbox.com/s/1phh02el8xh47 ... 1.mp4?dl=0

https://www.dropbox.com/s/b37kmxb296h4e ... 2.mp4?dl=0

Dave
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Re: Problems booting beeb issue 4

Post by DaveLecky » Mon Sep 30, 2019 2:20 pm

Hi 1024MAK,

WOW, so the computer must have had a new IC51 eprom put in at some time, which would have rendered the comp useless.

I will go for solution No.1, but I will have to order some sockets in first.

Here is my mainboard

E9866351-DF53-462C-9066-789D83DC6955.jpeg
Thanks

Dave
Last edited by DaveLecky on Mon Sep 30, 2019 2:39 pm, edited 1 time in total.
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Re: Problems booting beeb issue 4

Post by Boydie » Tue Oct 01, 2019 6:40 pm

All those screenshots look *very* familiar to me. Could this be a variant of my problem, giving a clock skewed in a slightly different way? Mine started as innocuous and became progressively more blatant as the chip failed.
What happens if you leave the machine on for a few minutes, and don’t reset?
As a simple clock test, my faults all got worse when the crystal, or the resistors around it were touched (with a finger or even more so with a suitable metallic object).

I understand money’s tight, but speaking as a newcomer to this, I’ve found an oscilloscope to be essential. Looking at Amazon, there seem to be a number of cheap scope kits around for not a lot of money (some about £20). Does anyone think these are adequate for (very) basic investigation?

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Re: Problems booting beeb issue 4

Post by 1024MAK » Tue Oct 01, 2019 7:59 pm

Really cheap oscilloscopes just don’t have the required frequency bandwidth to be useful. The absolute minimum bandwidth is 20MHz, but really it’s better to have 40MHz or higher. Similarly, the sampling rate of a digital ‘scope has to be fast enough to pick up the details of the signal.

Mark

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Re: Problems booting beeb issue 4

Post by Elminster » Tue Oct 01, 2019 10:10 pm

Some of the PC based scopes top out around 30 or 40Mhz and people have usable results with them. Not tried one myself, but Tricky has one.

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Re: Problems booting beeb issue 4

Post by DaveLecky » Thu Oct 03, 2019 2:25 pm

Hi there,

I made up the adapter as per instructions...

AE451FC7-E18E-4320-912F-B1F42B7C3FE5.jpeg

I tested continuity between 27,28 and 1......ok......(edited.)

Inserted the OS rom and pressed it firmly into the socket.

Switched on and got a continuous tone but nothing on screen.

I removed the adapter and replaced the OS rom...no change.

I checked the 5v from the power supply.....ok

I then placed Trickys test rom into socket and still no change.

I tried the above firstly with S25 north, then south then removed...no change.

Not sure where to go now....

Dave
Last edited by DaveLecky on Thu Oct 03, 2019 5:47 pm, edited 1 time in total.
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Re: Problems booting beeb issue 4

Post by DaveLecky » Thu Oct 03, 2019 2:28 pm

I’m now the proud owner of a logic probe.

0318C32A-7D78-4827-A475-6B424CB2F4E9.jpeg
49362C0B-1C06-4B81-84B1-2B32BC6FCB45.jpeg

Any good...?

Dave
Electron Plus 3 and plus 1, AP6 and Home made MMFS PP SD interface
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Beeb issue 7 with IFEL 16 socket Rom/Ram board, IFEL SD card, Floppy interface
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Wheel_nut
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Re: Problems booting beeb issue 4

Post by Wheel_nut » Thu Oct 03, 2019 3:56 pm

Looks good and should go the job for you. Like you, I needed one to diagnose the fault on my Beeb and bought one of these https://www.ebay.co.uk/itm/High-Logic-P ... 2749.l2649
Yours looks to be a lot more compact and has similar spec with the addition of the "buzzer".
#1 BBC Model B Issue 7 + 1770 DFS + Dual TEAC Floppy
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Elminster
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Re: Problems booting beeb issue 4

Post by Elminster » Thu Oct 03, 2019 4:37 pm

DaveLecky wrote:
Thu Oct 03, 2019 2:28 pm
I’m now the proud owner of a logic probe.

Any good...?

Dave
Looks identical to the one I got from RS, except that one is grey. And that one certainly does the job.

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1024MAK
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Re: Problems booting beeb issue 4

Post by 1024MAK » Thu Oct 03, 2019 5:05 pm

DaveLecky wrote:
Thu Oct 03, 2019 2:25 pm
I made up the adapter as per instructions...
DaveLecky wrote:
Thu Oct 03, 2019 2:25 pm
I tested continuity between 17,18 and 1.....ok
? :?:

Pin 1 on the top socket should be linked (and have continuity) to pins 27 and 28.
A OS ROM chip (no window and marked with an Acorn or IC manufacturers part number) and an EPROM with the Acorn OS code should both work correctly in the adapter.
DaveLecky wrote:
Thu Oct 03, 2019 2:25 pm
I then placed Trickys test rom into socket and still no change.

I tried the above firstly with S25 north, then south then removed...no change.
By no change, do you mean you still get a continuous tone and a blank screen?

Tricky’s test ROM does not care about the amount of working RAM, so it is best to configure the machine for both banks, 32K, S25 north.

Mark

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DaveLecky
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Re: Problems booting beeb issue 4

Post by DaveLecky » Thu Oct 03, 2019 5:44 pm

Hi 1024MAK,

Tested continuity between, 27,28 and 1......typo

No change to the single continuous tone and no screen output in any configuration I detailed.

I removed the adapter when I tried the original chip and Trickys in ic51.

Tried north, south and none to no avail.

Dave
Electron Plus 3 and plus 1, AP6 and Home made MMFS PP SD interface
Electron Plus 1 Pres AP3/4 with drive
Beeb issue 7 with IFEL 16 socket Rom/Ram board, IFEL SD card, Floppy interface
Master 128, BooBip multi OS,IFEL SD card
Cumana drives,Adder Programmer

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Re: Problems booting beeb issue 4

Post by Boydie » Thu Oct 03, 2019 6:43 pm

Dodgy OS rom socket? If it’s anything like the quality of the speech ones...
I’ve had this a few times. With a rom in the socket, try continuity testing between the shoulders of the rom and the soldered pin on the other side on the board.

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Re: Problems booting beeb issue 4

Post by Wheel_nut » Thu Oct 03, 2019 6:57 pm

Boydie wrote:
Thu Oct 03, 2019 6:43 pm
Dodgy OS rom socket? If it’s anything like the quality of the speech ones...
I’ve had this a few times. With a rom in the socket, try continuity testing between the shoulders of the rom and the soldered pin on the other side on the board.
I found this in a list of Beeb faults and solutions that I copied from a website.... I can't remember the source but this is #16 of about 60 items listed:

16. Poor Quality IC sockets with thin pins were used on Issue 4 boards. The pins snap off inside the socket housing - thus when re-soldered the broken pins drop out of the PCB.

Edit: Found the source : http://8bs.com/mag/37/bfaults.txt
Last edited by Wheel_nut on Thu Oct 03, 2019 7:08 pm, edited 1 time in total.
#1 BBC Model B Issue 7 + 1770 DFS + Dual TEAC Floppy
#2 BBC Model B Issue 7 + 8271 DFS + Dual Floppy + Speech + PiTubeDirect on KenLowe's Tube Level Shifter
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Re: Problems booting beeb issue 4

Post by DaveLecky » Thu Oct 03, 2019 7:05 pm

Yes I think it must be something like this..

My train of thought was cracked tracks on the reverse side of the board..it does seem to flex a bit...

I’ll try to check at least the os rom socket tonight.

Dave
Electron Plus 3 and plus 1, AP6 and Home made MMFS PP SD interface
Electron Plus 1 Pres AP3/4 with drive
Beeb issue 7 with IFEL 16 socket Rom/Ram board, IFEL SD card, Floppy interface
Master 128, BooBip multi OS,IFEL SD card
Cumana drives,Adder Programmer

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Re: Problems booting beeb issue 4

Post by DaveLecky » Thu Oct 03, 2019 7:32 pm

UPDATE.......UPDATE.......

Pins 27 and 28 are open circuit between the Ic leg and the solder joint on the rear of the board.

Looks promising... I just have to pluck up enough courage to desolder the little sucker...

Hints and tips gratefully accepted.

Dave
Electron Plus 3 and plus 1, AP6 and Home made MMFS PP SD interface
Electron Plus 1 Pres AP3/4 with drive
Beeb issue 7 with IFEL 16 socket Rom/Ram board, IFEL SD card, Floppy interface
Master 128, BooBip multi OS,IFEL SD card
Cumana drives,Adder Programmer

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