Archie Noob. Completed Restoration and could use some help

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1024MAK
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Re: Archie Noob. Completed Restoration and could use some help

Postby 1024MAK » Tue Sep 05, 2017 6:56 am

Schematic diagram:-Image

IC18 is the sound generator chip, a 76489.

See the photo of the Beeb's PCB complete with details of what each chip is on 8bs :wink:

What test equipment do you have?

Mark
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BradBrad
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Re: Archie Noob. Completed Restoration and could use some help

Postby BradBrad » Thu Sep 07, 2017 12:01 am

1024MAK wrote:
What test equipment do you have?

Mark


Cheers Mark, I reflowed that chip, reflowed the pins that connect to the speaker cable, tested with another speaker and tested the speaker cable. No difference. :?

I have a DMM, an old 20MHz Hameg scope (which I am a novice with), a variable bench power supply with current limit and a usb microscope.

Should I just socket and swap out IC18? It doesnt look damaged. I didn't check pinout yet.

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1024MAK
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Re: Archie Noob. Completed Restoration and could use some help

Postby 1024MAK » Thu Sep 07, 2017 7:38 am

If you have a 'scope, now is the time to learn how to use it to fault find :wink:

But before we get that far, with the computer switched off, measure the resistance of the speaker coil using the resistance range of your meter.

If okay, switch on and using BASIC or a music playing program, get the Beeb to output continuous sound.
In BASIC use:
SOUND 1,-15,184,-1
Press the ESCAPE key to shut it up! (Okay, once you have sound... :lol: ).

On IC18 (76489 the sound generator) pin 7 is the audio output. This is a good place to test.

If you can see a signal there, skip forward to IC17 (LM324) and test on pin 8.

Then if you get a signal, test on IC19 (LM386) pin 3 (input) and pin 5 (output). If you get a good audio signal here, it only leaves C16 (47uF) and the speaker.

In all cases, use AC coupling, the 'scope won't lock on (trigger and give a stable display) to a audio frequency if the frequency (note) is changing. So set the trigger to AUTO. The voltage level varies but is always below 5V. The frequency range is approximately the normal audio band. But if you find a 50Hz signal, that's the pick-up of the mains!

Mark
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1024MAK
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Re: Archie Noob. Completed Restoration and could use some help

Postby 1024MAK » Thu Sep 07, 2017 10:21 am

Here are some 'scope waveforms from my BBC B. Note that the 'scope I used is a PicoScope 3206MSO. Also note that these waveforms are a bit electrically noisy, both because the Beeb is electrically noisy and this 'scope does pick up some of the noise from the connected Laptop and adjacent gear.

BBC Model B, IC18 (76489) pin 7.PNG
IC18 (76489) pin 7

BBC Model B, IC17 (LM324) pin 8.PNG
IC17 (LM324) pin 8

BBC Model B, IC19 (LM386) pin 3.PNG
IC19 (LM386) pin 3

BBC Model B, IC19 (LM386) pin 5.PNG
IC19 (LM386) pin 5


Mark
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Re: Archie Noob. Completed Restoration and could use some help

Postby BradBrad » Thu Sep 07, 2017 3:28 pm

1024MAK wrote:If you have a 'scope, now is the time to learn how to use it to fault find :wink:

Mark



Wow, that is detailed! Thanks for taking the time with that. :D

So far, I have always restriced myself to using the 'scope on things that have no earth pin connection. So ground the scope to a nearby negative on a cap or something?

Scared myself watching vids about things being mains earth referenced and earth being linked to ground etc.

Cheers.

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danielj
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Re: Archie Noob. Completed Restoration and could use some help

Postby danielj » Thu Sep 07, 2017 6:08 pm

Indeed, negative from a capacitor or anywhere else near where you're measuring a signal. Failing that from anything else on ground - big metal bits etc... An oscilloscope is measuring relative to your ground connection.

d.

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Re: Archie Noob. Completed Restoration and could use some help

Postby BradBrad » Thu Sep 07, 2017 7:48 pm

danielj wrote:Indeed, negative from a capacitor or anywhere else near where you're measuring a signal. Failing that from anything else on ground - big metal bits etc... An oscilloscope is measuring relative to your ground connection.

d.


Thanks Daniel. I don't have an isolation transformer. Is that still OK? Sorry to bang on a bit :lol:

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Re: Archie Noob. Completed Restoration and could use some help

Postby danielj » Thu Sep 07, 2017 7:55 pm

Nope, I think you're fine :) Just be aware that you might see a 50Hz bit of interference here or there :D

d.

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1024MAK
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Re: Archie Noob. Completed Restoration and could use some help

Postby 1024MAK » Thu Sep 07, 2017 8:47 pm

The Beeb PSU connects it's output 0V rail to mains earth. A mains powered 'scope does the same. So as long as they are both plugged into the same ring main socket (or spur / radial circuit socket) there is no safety problem.

Just be careful that you don't accidentally short anything out with either the grounding lead or the 'scope probe.

Mark
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Re: Archie Noob. Completed Restoration and could use some help

Postby danielj » Thu Sep 07, 2017 9:48 pm

What's a little short between friends? It's how to test your fuses/RCDs are working :D

d.

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Re: Archie Noob. Completed Restoration and could use some help

Postby BradBrad » Thu Sep 07, 2017 11:53 pm

Cool guys. Thanks. Will try the suggested tests and see what I can find.... :D

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Re: Archie Noob. Completed Restoration and could use some help

Postby BradBrad » Fri Sep 08, 2017 3:28 pm

Quick update on the Archimedes. Bought a game on floppy (new and boxed :shock: ) Magic Pockets. Runs and plays fine (pic attached). Just have to figure out why the scart cable shifts everything on screen to the right a bit but the composite doesn't.

Still waiting for the IDE to SD card adapter. Wondering if it would take a Gotek as a second floppy drive? That would solve a lot of file transfer issues and, seeing as how the floppy drive works fine and is in really good condition, it seems a shame it swap it out.

Scoping the Beeb later... [-o<
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20170908_162119.jpg

BradBrad
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Re: Archie Noob. Completed Restoration and could use some help

Postby BradBrad » Fri Sep 08, 2017 3:29 pm

Of course, I'll have to build a joystick for it now too :shock:

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Re: Archie Noob. Completed Restoration and could use some help

Postby BradBrad » Sat Sep 09, 2017 7:10 pm

1024MAK wrote:Here are some 'scope waveforms from my BBC B.

Mark



Thanks Mark.

I finally dug out my 'scope and my old 10x probe. I can see what looks like 500mv peak to trough at 1mhz on pin 7 of IC18 (I see that whether or not I issue the SOUND command) :lol:
20170909_190011.jpg


I get complete garbage on pin 8 of IC 17 (the brand new and known working LM324.) Like I said. Not much of an expert :lol: . Think I'll swap out and socket IC18 and see how that goes.

20170909_194426.jpg

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1024MAK
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Re: Archie Noob. Completed Restoration and could use some help

Postby 1024MAK » Sun Sep 10, 2017 3:56 am

You need to be looking at frequencies only in the audio range (upto 20kHz). Not in the MHz range!

A 'scope will pick up higher frequencies that we are not interested in. So change your timebase setting. If your 'scope has a trigger setting that filters out high frequencies, use that setting (it won't filter out high frequencies from the displayed trace, but reduces the sensitivity of the trigger circuit to high frequency signals).

You can check the analogue side (LM324 and LM386) by using a short length of thin solid core wire (with the ends stripped) so that when you touch one end with your hand and touch it on the input pins of LM324 and LM386, if they are working, you should hear mains hum from the loud speaker.

Mark
For a "Complete BBC Games Archive" visit www.bbcmicro.co.uk NOW!
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BradBrad
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Re: Archie Noob. Completed Restoration and could use some help

Postby BradBrad » Thu Sep 14, 2017 1:18 pm

Thanks for all the help.

It was IC18. Replaced and working fine. Now just to replace the missing key...

I designed the best approximation as I could in sketchup anf 3d Printed it in black PLA. The switch from EBay just arrived too :D

Do you retrobrite these cases or just use bleach?
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20170914_141314.jpg

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Re: Archie Noob. Completed Restoration and could use some help

Postby jms2 » Thu Sep 14, 2017 5:05 pm

Opinions differ on the use of Retrobrite. I've used it, and it seems to work OK. I have not tried bleach - not sure whether that works.

Some people prefer to keep their Beeb in an authentic yellowed state though.

BradBrad
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Re: Archie Noob. Completed Restoration and could use some help

Postby BradBrad » Thu Sep 14, 2017 8:34 pm

Thanks. Think i'll give it a go anyway. It is much better now than when I received it but that isn't saying much :lol: Still very grubby.

Filled the hole in the keyboard with a 3d printed part and put the 3d printed key on the new keyswitch. At least it is all in one piece now. Pics attached. If anyone wants the Sketchup and STL files for the keycap then let me know. Maybe somebody can improve it. Better than having a hole there :shock:

Just need to get some software onto it now. The only thing that will load via my Heath Robinson Tapdancer setup is Chuckie Egg. :roll:

Still waitin on parts for the Archy.
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20170914_212309.jpg

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Re: Archie Noob. Completed Restoration and could use some help

Postby jms2 » Sun Sep 24, 2017 6:11 pm

Brad asked me for a disc image of the !IDEmgr application. I found two, which might be identical... the first one is !IDEmgr v1.10, not sure what the other one is but it is labelled as being for the v5.00 rom.

idemgr.zip
(69.51 KiB) Downloaded 4 times

HCCS IDEMGR for V5_00.zip
(84.24 KiB) Downloaded 2 times


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