My new beeb - A to B? But why no analogue?

discuss both original and modern hardware for the bbc micro/electron
iamaran
Posts: 354
Joined: Tue Mar 14, 2006 8:08 pm
Contact:

My new beeb - A to B? But why no analogue?

Post by iamaran » Sat Feb 16, 2019 1:21 am

Back in the day I had an Issue 7 Model B (presumably in silicon heaven as I sadly sold it to fund an Amiga). Now I'm the proud owner of an Issue 3 ICL built model.

My first impression of my new Beeb is that it is a Model A upgraded to B spec because 8 of the 16 RAM chips are clearly different.

The RS423 and RGB are present but the analogue isn't. The tube, user port, etc underneath are all there so my question is: this "Why would a Model A be upgraded to a B spec in every respect I can think of, except for the analogue port?"

Or did ICL do it differently? Am I missing something obvious? Or... ?

I can't/won't power it on until I replace the PSU caps or pay for that to be done for me.

Quick snaps attached, better photos can be taken this weekend.

Thanks for any input everyone.
Attachments
rear.jpg
under.JPG
ram.JPG
Last edited by iamaran on Sat Feb 16, 2019 1:34 am, edited 1 time in total.

duikkie
Posts: 2986
Joined: Fri Feb 07, 2014 3:28 pm
Contact:

Re: My new beeb - A to B? But why no analogue?

Post by duikkie » Sat Feb 16, 2019 6:51 am

Take a picture of thee pcb board in totale The bbc was a learning computer and te analoge port was for. Play ing :)
Last edited by duikkie on Sat Feb 16, 2019 6:51 am, edited 1 time in total.

User avatar
tricky
Posts: 4364
Joined: Tue Jun 21, 2011 9:25 am
Contact:

Re: My new beeb - A to B? But why no analogue?

Post by tricky » Sat Feb 16, 2019 8:10 am

I've come across a couple where the connector has been hanging off and one where the d7002 was toast!

User avatar
1024MAK
Posts: 10009
Joined: Mon Apr 18, 2011 5:46 pm
Location: Looking forward to summer in Somerset, UK...
Contact:

Re: My new beeb - A to B? But why no analogue?

Post by 1024MAK » Sat Feb 16, 2019 9:15 am

It may help if you have a look at the underside/solder side. Look at the component and chip pads. Flow soldered pads are normally clean and very consistent. If you see any flux (black/brown/tan coloured deposits) around solder joints / pads, or the solder joints are not consistent (varying amounts of solder on each pin/pad), these are signs of hand soldering.

As to why the analogue port connector was not fitted, we can only speculate. Are you sure it was never fitted? Or was it broken off? Is the analogue to digital converter (ADC) chip fitted?

It may be the owner at the time was not a game player, or maybe they hated joysticks. Or maybe the machine was only intended for serious use.

Mark
Last edited by 1024MAK on Sat Feb 16, 2019 10:42 am, edited 1 time in total.

cmorley
Posts: 1260
Joined: Sat Jul 30, 2016 8:11 pm
Location: Oxford
Contact:

Re: My new beeb - A to B? But why no analogue?

Post by cmorley » Sat Feb 16, 2019 10:00 am

Probably just cost. Why pay for it if you're not going to use it?

As Mark says some photos of the area and solder side might hint to the history of this machine.

iamaran
Posts: 354
Joined: Tue Mar 14, 2006 8:08 pm
Contact:

Re: My new beeb - A to B? But why no analogue?

Post by iamaran » Sat Feb 16, 2019 10:12 am

Thanks all. Now I look with eyes that aren't tired...
Attachments
P1120078.JPG

User avatar
1024MAK
Posts: 10009
Joined: Mon Apr 18, 2011 5:46 pm
Location: Looking forward to summer in Somerset, UK...
Contact:

Re: My new beeb - A to B? But why no analogue?

Post by 1024MAK » Sat Feb 16, 2019 10:31 am

So the ADC chip is fitted :?

Mark

cmorley
Posts: 1260
Joined: Sat Jul 30, 2016 8:11 pm
Location: Oxford
Contact:

Re: My new beeb - A to B? But why no analogue?

Post by cmorley » Sat Feb 16, 2019 10:34 am

The chip is there. Perhaps the socket got corroded and was removed...

User avatar
tricky
Posts: 4364
Joined: Tue Jun 21, 2011 9:25 am
Contact:

Re: My new beeb - A to B? But why no analogue?

Post by tricky » Sat Feb 16, 2019 10:37 am

As it has the A2D chip, I suspect it has been worked loose/broken and was there at some point.
Some beebs seem to have the 15pin connector "push" fit to the board, held in by the two screws.
I don't know if this is how they were supposed to be or if the pins have all broken off leaving little stubs, but either way over-tighten the screws a few times and you'll strip the threads and have no analogue port.

User avatar
1024MAK
Posts: 10009
Joined: Mon Apr 18, 2011 5:46 pm
Location: Looking forward to summer in Somerset, UK...
Contact:

Re: My new beeb - A to B? But why no analogue?

Post by 1024MAK » Sat Feb 16, 2019 10:48 am

Some have a 15 way D connector that has solder tabs to secure it to the PCB rather than screws or machine screws/bolts and nuts.

Mark

johnkenyon
Posts: 242
Joined: Wed Jul 20, 2011 3:21 pm
Location: Coventry
Contact:

Re: My new beeb - A to B? But why no analogue?

Post by johnkenyon » Sat Feb 16, 2019 12:17 pm

The ADC socket looks like it's been installed and removed.
It's also got a speech synth upgrade installed - TMS5220 + TMS6100.

User avatar
tricky
Posts: 4364
Joined: Tue Jun 21, 2011 9:25 am
Contact:

Re: My new beeb - A to B? But why no analogue?

Post by tricky » Sat Feb 16, 2019 12:41 pm

I've replaced the resistor with a variable one on a couple of my issue 3 beebs where the speech frequency was too far off, but yours is probably fine if it was done by a dealer, also they don't have to be spot on, the pitch just sounds a bit off.

iamaran
Posts: 354
Joined: Tue Mar 14, 2006 8:08 pm
Contact:

Re: My new beeb - A to B? But why no analogue?

Post by iamaran » Sat Feb 16, 2019 12:46 pm

Right, thanks everyone. Replacing it will be beyond my skills! I will get the PSU done (though it does look ok to this novice) and see whether it powers on.
Attachments
P1120081.JPG

cmorley
Posts: 1260
Joined: Sat Jul 30, 2016 8:11 pm
Location: Oxford
Contact:

Re: My new beeb - A to B? But why no analogue?

Post by cmorley » Sat Feb 16, 2019 12:58 pm

It's the orange/yellow translucent RIFA caps that fail with the burning paper smell. They die with age so replacing them saves setting off your smoke alarm and so popping/fizzing noises + the lingering stench!

You can see one in the photo and the other is hiding under the mains wiring.

I replace them with Kemet poly caps which don't fail by way of fire and smoke. Others replace like for like but they will fail again given time.

They are easy to replace.

iamaran
Posts: 354
Joined: Tue Mar 14, 2006 8:08 pm
Contact:

Re: My new beeb - A to B? But why no analogue?

Post by iamaran » Wed Feb 27, 2019 8:40 pm

It lives!

BBC Computer 32K
Acorn DFS
BASIC

*H.
WORDWISE-PLUS 1.48
DFS 0.9H
DFS
UTILS
OS 1.20

The 5 ROMs are (I think):
IC51 HN613128PB04 OS 1.2
IC52 Torch Computers (but would appear to be Acorn) DFS .9H
IC88 Wordwise Plus 1.48
IC100 HN613128PB05 BASIC II
IC101 HN613128PB01 BASIC I

And Kenneth Kendal talks perfectly!

I'm sorry for all the questions that will surely follow, but it's been a very long time since I owned an issue 7.

Q1: Are my ROM assumptions correct from the photo? I do miss the *ROMS command!
Q2: Why two BASIC ROMs? REPORT replies 1981 suggesting BASIC I.

Thanks everyone.
Attachments
IMG_6690.JPG

User avatar
Pernod
Posts: 2034
Joined: Fri Jun 08, 2012 11:01 pm
Location: Croydon, UK
Contact:

Re: My new beeb - A to B? But why no analogue?

Post by Pernod » Wed Feb 27, 2019 9:08 pm

iamaran wrote:
Wed Feb 27, 2019 8:40 pm
Q1: Are my ROM assumptions correct from the photo? I do miss the *ROMS command!
Correct, though I would like to see a dump of the DFS 0.9H.
iamaran wrote:
Wed Feb 27, 2019 8:40 pm
Q2: Why two BASIC ROMs? REPORT replies 1981 suggesting BASIC I.
You don't need both. It's finding BASIC1 first, simply remove it and REPORT will reply 1982.
- Nigel

BBC Model B: ATPL Sidewise, Acorn Speech, 2xWatford Floppy Drives, AMX Mouse, Viglen case, BeebZIF, etc.

iamaran
Posts: 354
Joined: Tue Mar 14, 2006 8:08 pm
Contact:

Re: My new beeb - A to B? But why no analogue?

Post by iamaran » Wed Feb 27, 2019 9:37 pm

Pernod wrote:
Wed Feb 27, 2019 9:08 pm
iamaran wrote:
Wed Feb 27, 2019 8:40 pm
Q1: Are my ROM assumptions correct from the photo? I do miss the *ROMS command!
Correct, though I would like to see a dump of the DFS 0.9H.
As soon as I'm in a position to do so, I promise to do this.
Last edited by iamaran on Wed Feb 27, 2019 9:38 pm, edited 1 time in total.

iamaran
Posts: 354
Joined: Tue Mar 14, 2006 8:08 pm
Contact:

Re: My new beeb - A to B? But why no analogue?

Post by iamaran » Wed Feb 27, 2019 9:39 pm

Pernod wrote:
Wed Feb 27, 2019 9:08 pm
iamaran wrote:
Wed Feb 27, 2019 8:40 pm
Q2: Why two BASIC ROMs? REPORT replies 1981 suggesting BASIC I.
You don't need both. It's finding BASIC1 first, simply remove it and REPORT will reply 1982.
Yep, that works. Thanks! Odd, because the previous owner was savvy and has 3 or 4 in his (now my) collection (DiscDoctor, Exmon etc) that he could have replaced it with.
Last edited by iamaran on Wed Feb 27, 2019 9:45 pm, edited 2 times in total.

smokey
Posts: 19
Joined: Mon Mar 04, 2019 5:52 pm
Contact:

Re: My new beeb - A to B? But why no analogue?

Post by smokey » Mon Mar 04, 2019 8:34 pm

to me. it looks like an "upgraded" Model A

BUT i might be very wrong.

If i am wrong why would a model b be missing ports.

James

iamaran
Posts: 354
Joined: Tue Mar 14, 2006 8:08 pm
Contact:

Re: My new beeb - A to B? But why no analogue?

Post by iamaran » Fri Mar 08, 2019 8:01 pm

iamaran wrote:
Wed Feb 27, 2019 9:37 pm
Pernod wrote:
Wed Feb 27, 2019 9:08 pm
iamaran wrote:
Wed Feb 27, 2019 8:40 pm
Q1: Are my ROM assumptions correct from the photo? I do miss the *ROMS command!
Correct, though I would like to see a dump of the DFS 0.9H.
As soon as I'm in a position to do so, I promise to do this.
ROM dumped. Will post in Archive Submissions.

iamaran
Posts: 354
Joined: Tue Mar 14, 2006 8:08 pm
Contact:

Re: My new beeb - A to B? But why no analogue?

Post by iamaran » Sun Feb 16, 2020 7:06 pm

Hi all. Exactly one year after I got it, it has stopped working :(

It has been behaving badly recently, often displaying 16K instead of 32 and also the common graphics corruption - Ferranti 5C094E-3 ULA (1982). So today I decided to clean up the ULA by removing the decades old thermal porridge and using some Arctic Silver 5 with the original heatsink.

It now powers up (as in caps lock is lit) but there is no beep and no display. There is a noise from the speaker, but that's just static.

Any ideas gratefully received. Thanks.

Kazzie
Posts: 1618
Joined: Sun Oct 15, 2017 8:10 pm
Location: North Wales
Contact:

Re: My new beeb - A to B? But why no analogue?

Post by Kazzie » Mon Feb 17, 2020 6:24 am

iamaran wrote:
Sun Feb 16, 2020 7:06 pm
Hi all. Exactly one year after I got it, it has stopped working :(

It has been behaving badly recently, often displaying 16K instead of 32 and also the common graphics corruption - Ferranti 5C094E-3 ULA (1982). So today I decided to clean up the ULA by removing the decades old thermal porridge and using some Arctic Silver 5 with the original heatsink.

It now powers up (as in caps lock is lit) but there is no beep and no display. There is a noise from the speaker, but that's just static.

Any ideas gratefully received. Thanks.
The fact that your machine had started forgetting whether it had 16k or 32k of RAM suggests that its fault may be either in one of the RAM banks, or in the support circuitry around it. The lack of noise from the speaker is a bit unusual, as the sound chip defaults to making noise when it's powered up - that's what causes the first beep. (Are you confident you've got the speaker plugged into the board correctly)

:arrow: Have you tried booting the machine with jumper S25 moved to the South position, or Removed altogether? These configurations force the machine to use only one 16K RAM bank. (See this post on the fault-finding thread for a detailed explanation.)

:arrow: If we need to start poking and measuring bits of your machine, what testing equipment (e.g. multimeter, logic probe, oscilloscope) do you have available?
BBC Model B 32k issue 7, Sidewise ROM board with 16K RAM
Archimedes 420/1 upgraded to 4MB RAM, ZIDEFS with 512MB CF card
Acorn System 1 home-made replica

iamaran
Posts: 354
Joined: Tue Mar 14, 2006 8:08 pm
Contact:

Re: My new beeb - A to B? But why no analogue?

Post by iamaran » Mon Feb 17, 2020 8:07 pm

Thanks for the reply Kazzie, you’re always helping me out!

Yes the speaker is definitely connected correctly.

Yes I have tried booting with the jumper on S25 moved and also with the jumper removed.

I can borrow a multimeter, but if you remember last time was the first time I’ve used in all my 48 years!

Small update, I am getting a very short beep approximately every 5 or so times I switch it on. Wav and mp3 attached (first noise is switch with no beep, second is switch and short "bip").
Attachments
Bip.mp3
(64.9 KiB) Downloaded 10 times
Bip (wav).zip
(165.76 KiB) Downloaded 9 times

Kazzie
Posts: 1618
Joined: Sun Oct 15, 2017 8:10 pm
Location: North Wales
Contact:

Re: My new beeb - A to B? But why no analogue?

Post by Kazzie » Mon Feb 17, 2020 9:33 pm

You had me racking my brains there... I couldn't recall helping you with your Beeb before, then a quick forum search reminded me that our last patient was a floppy drive! :)

The 76489 sound generator chip used in the Beeb (IC18) is "on" (generating random noise) when powered up, as that's what causes the first "booo" when you flick the switch: that's the time the chip is powered before the OS gets around to giving it a "mute" instruction. As your chip isn't making any noise (or hardly any), I'm wondering if it's being powered properly. You have a keyboard LED lit, but red LEDs will light up with as little as 2V over them; integrated circuits are typically a bit pickier.

Could you use a voltmeter to check the voltage being supplied to the mainboard by the power supply? There are three pairs of red and black cables (5V and ground, respectively) that are attached to the board with spade connectors. Set your voltmeter to a suitable voltage range, and measure the voltage between each pair of connectors. Try to make sure the meter probes are touching the mainboard's connector rather than the cable's connector: we want to be sure we're measuring the voltage that the board is actually getting. You'd expect to get a value between 4.75V and 5.25V.

The purple cable carries -5V to the board. The audio amplifier is one of the few bits of the Beeb that needs this negative voltage, so it's worth checking this too. Measure the voltage between the -5V connector and any nearby Ground connector, using the same technique as above. If you need any further guidance, just ask.

(What issue board do you have? Earlier boards have the +5V connectors supplying separate portions of the board; later boards have the +5V connected together on the board.)

If the voltages are all fine, the next possibility that springs to mind is a lack of a 4MHz clock signal being fed to the 76489. If that's missing on the sound chip, it's probably indicative of a fault with the clock generation circuitry. We can do some basic tests with a voltmeter, but we'll look at that after making sure our power supply is healthy.
BBC Model B 32k issue 7, Sidewise ROM board with 16K RAM
Archimedes 420/1 upgraded to 4MB RAM, ZIDEFS with 512MB CF card
Acorn System 1 home-made replica

iamaran
Posts: 354
Joined: Tue Mar 14, 2006 8:08 pm
Contact:

Re: My new beeb - A to B? But why no analogue?

Post by iamaran » Mon Feb 17, 2020 11:01 pm

Thanks Kazzie, I will certainly do that asap. It’s an Issue 3 board.

I do have another self-inflicted problem now though – I’ve broken one of the male terminal posts at VCC3. The spade connector was stiff but I did think I was being relatively gentle!

User avatar
1024MAK
Posts: 10009
Joined: Mon Apr 18, 2011 5:46 pm
Location: Looking forward to summer in Somerset, UK...
Contact:

Re: My new beeb - A to B? But why no analogue?

Post by 1024MAK » Tue Feb 18, 2020 1:23 am

On an issue 3 board, if one of the VCC (+5V) connections is faulty or open circuit, one third of the board will not be powered...

You still need to carry out the voltage tests to confirm if the PSU is working correctly.

Mark

iamaran
Posts: 354
Joined: Tue Mar 14, 2006 8:08 pm
Contact:

Re: My new beeb - A to B? But why no analogue?

Post by iamaran » Tue Feb 25, 2020 8:48 pm

Hi again, and thanks Kazzie and 1024MAK. I am so sorry for the delay, life keeps getting in the way.
So, with the multimeter set to 20V DC range, I am getting the following healthy looking values:

VCC1: 5.06
VCC2: 5.03
VCC3: Can’t measure due to me having broken a post
-5V: -4.83

I wasn’t rough with the post that I broke, and I’ll probably end up soldering the wire directly on.

Kazzie
Posts: 1618
Joined: Sun Oct 15, 2017 8:10 pm
Location: North Wales
Contact:

Re: My new beeb - A to B? But why no analogue?

Post by Kazzie » Thu Feb 27, 2020 12:10 pm

Those voltages are all within specification. So for ther to be no sound at all, I suspect a lack of a clock signal.

Testing with a multimeter isn't as good as an oscilloscope for kooling at clock signals, but it can give some indication of whether there's any signal present. (I can't recall if you have a logic probe, if you do, then repeating the following tests with that will tell us if the voltage is fixed or strobing.)

Could you please take a DC voltage reading of the following pins:

:arrow: IC18 (76489) pins 8, 14, and 16
checking the power to the sound chip, and the clock input

:arrow: IC6 (video chip) pins 4, 5, 6, 7, 8
checking the 16MHz master clock, and the other clock signals derived from it

Take care to measure the voltage on the pin shoulders, rather than the socket contacts, to make sure you're reading what the chip sees.
BBC Model B 32k issue 7, Sidewise ROM board with 16K RAM
Archimedes 420/1 upgraded to 4MB RAM, ZIDEFS with 512MB CF card
Acorn System 1 home-made replica

iamaran
Posts: 354
Joined: Tue Mar 14, 2006 8:08 pm
Contact:

Re: My new beeb - A to B? But why no analogue?

Post by iamaran » Thu Feb 27, 2020 10:28 pm

Thank you Kazzie. I don't have probe, just a cheapy multimeter. DC voltages are as follows:

IC18
8 - 0
14 - 1.58
16 - 5.02

IC6
4 - 0.46
5 - 1.77
6 - 1.74
7 - 2.06
8 - 0.98

Kazzie
Posts: 1618
Joined: Sun Oct 15, 2017 8:10 pm
Location: North Wales
Contact:

Re: My new beeb - A to B? But why no analogue?

Post by Kazzie » Fri Feb 28, 2020 10:37 am

Your cheapy multimeter has given us useful measurements, no matter what its price was!

Pins 8 and 16 on IC18 show us that the sound chip is getting power correctly.

The 1.58V reading on the clock input (pin 14) isn't the expected value. An ideal square wave clock signal, that spends half its time at 5V and half its time at 0V, would give a DC average of 2.5V. Realistically, this average may be slightly lower, around 2.4V or 2.3V. But 1.58V is well off.

There are a few possible explanations for this lower average, including:
  • The voltage goes up to 5V, but for only half as long as it's at 0V (this can't be the case, as that would make the 76489 chip run and make noises)
  • The voltage only goes up as far as ~3V, before coming back down to 0V
  • The voltage isn't actually changing, and is fixed at 1.58V
Either way, the readings from IC6 indicate that this is a problem from the clock generation area:
BBC-clock.png
The crystal and three inverter gates from IC43 resonate at 16MHz, and the gate from IC40 tidies this clock signal up a bit. The video processor (IC6) then halves this clock signal repeatedly to generate the 8MHz, 4MHz, 2MHz and 1MHz clock signals.

A quick poke in my own Beeb this morning showed DC voltage readings of 2.5V - 2.3V for pins 4-7, with an input signal on pin 8 at around 1.8V. Your output voltages are well below this mark, but so is your input on pin 8. On that basis, IC6 is probably not to blame, rather it's getting a poor imitation of a 16MHz input signal from the oscillator.

We've narrowed the problem to a specific area, but nailing it down exactly will be difficult with just a voltmeter.

:arrow: You could measure the voltage at pins 11, 12 and 13 of IC40 (74s00), and pin 6 on IC43 (74s04), which may indicate if IC40 is faulty. (Measuring pins 1-5 of IC43 is unlikely to be useful, as the capacitance of a meter probe to the resonant circuit will probably alter its behaviour.)

After that, other options would include checking the area for any poor solder joints, and the speculative replacement of IC43, the 16MHz crystal, or the capcitors CC37, C40, or C42 to see if they're at fault.

Note that if replacing the 74xx ICs in this area, it's important that you replace them with equivalents from the 74s series, not 74ls or other varieties. Different varieties have varying timing characterisics, and timing is of course very important in a clock generation circuit. ;)
BBC Model B 32k issue 7, Sidewise ROM board with 16K RAM
Archimedes 420/1 upgraded to 4MB RAM, ZIDEFS with 512MB CF card
Acorn System 1 home-made replica

Post Reply

Return to “8-bit acorn hardware”