Master ET (Econet Terminal)

discuss both original and modern hardware for the bbc micro/electron
Post Reply
Ottly
Posts: 152
Joined: Tue Jun 10, 2014 11:34 am
Contact:

Master ET (Econet Terminal)

Post by Ottly » Fri Nov 02, 2018 1:52 am

Hi All,

I have a Master ET workstation that was working but now is giving me the continuous beep of death. I know a dodgy ROM can cause this and given the current ROM in the machine is an EPROM I'm wondering if its failed. I have a Master 128 and was wondering are the OS ROMS compatible between the 2 machines? I've tried the Master ET ROM in my Master 128 and it doesn't work. But I've also tried the working ROM in my Master 128 in the Master ET and its not working there either.

Thanks, Scott.

User avatar
jgharston
Posts: 4008
Joined: Thu Sep 24, 2009 12:22 pm
Location: Whitby/Sheffield
Contact:

Re: Master ET (Econet Terminal)

Post by jgharston » Fri Nov 02, 2018 9:03 am

Ottly wrote:
Fri Nov 02, 2018 1:52 am
I have a Master 128 and was wondering are the OS ROMS compatible between the 2 machines? I've tried the Master ET ROM in my Master 128 and it doesn't work. But I've also tried the working ROM in my Master 128 in the Master ET and its not working there either.
The machine is nearly identical. The Master ET ROM is 4x16K instead of 8x16K, so to use the Master 128 MOS you need to change LINK 9 from 64K to 128K.

Code: Select all

$ bbcbasic
PDP11 BBC BASIC IV Version 0.32
(C) Copyright J.G.Harston 1989,2005-2020
>_

User avatar
danielj
Posts: 8165
Joined: Thu Oct 02, 2008 5:51 pm
Location: Manchester
Contact:

Re: Master ET (Econet Terminal)

Post by danielj » Fri Nov 02, 2018 9:05 am

First port of call when this happens is always the System VIA (6522)...

d.

Ottly
Posts: 152
Joined: Tue Jun 10, 2014 11:34 am
Contact:

Re: Master ET (Econet Terminal)

Post by Ottly » Fri Nov 02, 2018 10:18 am

jgharston wrote:
Fri Nov 02, 2018 9:03 am
The machine is nearly identical. The Master ET ROM is 4x16K instead of 8x16K, so to use the Master 128 MOS you need to change LINK 9 from 64K to 128K.
Thanks Jonathan.
danielj wrote:
Fri Nov 02, 2018 9:05 am
First port of call when this happens is always the System VIA (6522)...

d.
Thanks Daniel, does that mean de-soldering the chip and swapping it out or are there some tests I can do prior to this? I have a oscilloscope if that helps.

Scott.

User avatar
danielj
Posts: 8165
Joined: Thu Oct 02, 2008 5:51 pm
Location: Manchester
Contact:

Re: Master ET (Econet Terminal)

Post by danielj » Fri Nov 02, 2018 10:27 am

Swapping it for a known good one is the usual method. I'm not quite sure how a mucked up 6522 in a master would manifest when looking at signals. On the beeb I think if you remove the dead one you can get it to boot (although obviously the keyboard won't work), but not sure about the master.

d.

User avatar
geraldholdsworth
Posts: 626
Joined: Tue Nov 04, 2014 9:42 pm
Location: Inverness, Scotland
Contact:

Re: Master ET (Econet Terminal)

Post by geraldholdsworth » Fri Nov 02, 2018 11:20 am

Couldn't you swap the two VIAs in a Master?
Annoying that they need to be desoldered - as this has the possibility of damaging them.
Gerald Holdsworth
Repton Resource Page
www.reptonresourcepage.co.uk

User avatar
danielj
Posts: 8165
Joined: Thu Oct 02, 2008 5:51 pm
Location: Manchester
Contact:

Re: Master ET (Econet Terminal)

Post by danielj » Fri Nov 02, 2018 11:28 am

The econet terminal only has a system via, no user via :(

d.

User avatar
jgharston
Posts: 4008
Joined: Thu Sep 24, 2009 12:22 pm
Location: Whitby/Sheffield
Contact:

Re: Master ET (Econet Terminal)

Post by jgharston » Fri Nov 02, 2018 8:23 pm

danielj wrote:
Fri Nov 02, 2018 11:28 am
The econet terminal only has a system via, no user via :(
Yes, from memory the ET is missing:
* user port/printer port (user VIA)
* analogue port
* Tube buffers
* disk interface
and has a 4x16K system ROM: MOS, Utils, ANFS, BASIC instead of the
8x16K system ROM: MOS, Utils, View, ADFS, BASIC, ViewSheet, Edit, DFS
The system ROM is almost the same as the Compact: MOS, Utils, ADFS, BASIC.

Code: Select all

$ bbcbasic
PDP11 BBC BASIC IV Version 0.32
(C) Copyright J.G.Harston 1989,2005-2020
>_

User avatar
BeebMaster
Posts: 3311
Joined: Sun Aug 02, 2009 5:59 pm
Location: Lost in the BeebVault!
Contact:

Re: Master ET (Econet Terminal)

Post by BeebMaster » Sat Nov 03, 2018 1:19 pm

For what it's worth pictures of my Master ET are here, although they are chronic and I can't find the original camera images to re-process the set.

That machine came from a STH member who had upgraded it for use as a Level 3 File Server station.
Image

User avatar
BeebMaster
Posts: 3311
Joined: Sun Aug 02, 2009 5:59 pm
Location: Lost in the BeebVault!
Contact:

Re: Master ET (Econet Terminal)

Post by BeebMaster » Sat Nov 03, 2018 1:46 pm

Found them now, here is the best picture of the board.
HPIM1227.JPG
Image

Ottly
Posts: 152
Joined: Tue Jun 10, 2014 11:34 am
Contact:

Re: Master ET (Econet Terminal)

Post by Ottly » Sun Nov 04, 2018 5:56 am

Thanks everyone for your help.

My master ET is about to go under the knife now and extract the 6522.

I tried LK9 and the ROM from my master 128 with no luck.

Its weird how its just died. I haven't used this machine much at all.
Master ET.jpg
Last edited by Ottly on Sun Nov 04, 2018 7:46 am, edited 3 times in total.

Ottly
Posts: 152
Joined: Tue Jun 10, 2014 11:34 am
Contact:

Re: Master ET (Econet Terminal)

Post by Ottly » Sun Nov 04, 2018 7:09 am

Ok, i've successfully extracted the 6522 from IC8 on the Master ET. I put the extracted 6522 into my model B and its working fine. I've tried the working 6522 from the Model B and tried it in the Master ET. Still have beep of death. What are the next steps with troubleshooting this one?

Each time I power the machine on the beep of death sounds different. Sometimes loud, other times soft. Don't know if this helps with pin pointing the issue?

Power supply is outputting 5.1V and -5.1V.
Last edited by Ottly on Sun Nov 04, 2018 7:30 am, edited 2 times in total.

Ottly
Posts: 152
Joined: Tue Jun 10, 2014 11:34 am
Contact:

Re: Master ET (Econet Terminal)

Post by Ottly » Sun Nov 04, 2018 12:44 pm

Ok I've made some progress. I noticed the Reset line being held LOW on the 6502. I traced this back on the schematic to IC39 then back to IC19.

If I hold PIN 12 low on IC39 the machine boots to the ACORN MOS this is not a language. So I need to find out whats holding the reset line LOW. Schematic says KBD SW to sheet2. so trying to work out where that is and whats causing it.
Last edited by Ottly on Sun Nov 04, 2018 12:47 pm, edited 1 time in total.

Ottly
Posts: 152
Joined: Tue Jun 10, 2014 11:34 am
Contact:

Re: Master ET (Econet Terminal)

Post by Ottly » Sun Nov 04, 2018 1:41 pm

Ok, so it looks like its either a faulty resistor R53 10K, a faulty diode D13 1N4148 or a faulty capacitor C22 100nf. These are used to hold the reset line HIGH and will only go low when the break key is pressed on the keyboard performing a reset of the 6502 CPU.

So which component would you swap out and replace first?

The resistor and diode are connected to +5V, the capacitor to ground.

My guess is the capacitor as that's the only way to ground for the current to flow other then the break key being pressed which I know isn't at fault.

Is my logic on track here? Although I find it a little odd that any of these discrete components would fail. It is a ceramic capacitor.

If I apply 5V to the circuit it jumps up to 5V and slowly drops down (sometimes a big drop down to 1V or .5V), once below 1.3V the machine fails to respond to any keystrokes. Just like holding down on the break key.
Last edited by Ottly on Sun Nov 04, 2018 2:02 pm, edited 5 times in total.

Kazzie
Posts: 1592
Joined: Sun Oct 15, 2017 8:10 pm
Location: North Wales
Contact:

Re: Master ET (Econet Terminal)

Post by Kazzie » Sun Nov 04, 2018 7:29 pm

Have you checked the voltage either side of R48 (which leads to the keyboard connector)? If the keyboard side of it is low, then the fault would seem to be on your keyboard.

You could check R53's health in-situ with a multmeter: check the voltage either side, and then measure the resistance across it. (Measure both ways round, as the diode should short the resistor in one direction.)
Ottly wrote:
Sun Nov 04, 2018 12:44 pm
Ok I've made some progress. I noticed the Reset line being held LOW on the 6502. I traced this back on the schematic to IC39 then back to IC19.

If I hold PIN 12 low on IC39 the machine boots to the ACORN MOS this is not a language.
I presume you meant pin 12 of IC19?
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

User avatar
1024MAK
Posts: 9988
Joined: Mon Apr 18, 2011 5:46 pm
Location: Looking forward to summer in Somerset, UK...
Contact:

Re: Master ET (Econet Terminal)

Post by 1024MAK » Sun Nov 04, 2018 9:48 pm

Lift one end of R48 :wink:

Mark

Post Reply

Return to “8-bit acorn hardware”