Master 128 CMOS Fault - SOLVED

discuss both original and modern hardware for the bbc micro/electron
Post Reply
User avatar
DaveLecky
Posts: 283
Joined: Mon Jul 08, 2019 7:52 am
Location: Airdrie, Scotland
Contact:

Master 128 CMOS Fault - SOLVED

Post by DaveLecky » Fri Sep 18, 2020 9:12 pm

Hi Folks,

I was given this master 128 and can’t find a solution to the problem, can anyone help please.

It appears that the configure settings are scrambled and won’t reset.

I have checked the keyboard and MOS 3.2 chip on working 128, a new backup battery has been fitted, the voltages are ok when switched on or off.

Switching power on I get a lot of bagpipe tones and,
TERMINAL
=
Power light and Caps Lock on, keyboard is mainly inactive, except for Ctrl Break, so nothing changes with the usual resets, Ctrl F break etc.
On occasion Ctrl Break has a reaction which gives , Acorn MOS, Acorn ADFS/DFS and flashing cursor. If I connect a disc drive it attempts to read it, displaying,
**BASIC
Bad Command
**LIB $.Library
**DIR $.Welcome
*CHAIN “Init”
Bad Command
*
Keyboard won’t function other than Ctrl Break which takes me back to TERMINAL =

Switching on with R pressed I get Acorn MOS, Acorn ADFS/DFS etc again as above, and reads the disc again.
Sometimes it refers to Acorn MOS, Acorn 1770 DFS with cursor.
While Ctrl Breaking, the screen mode sometimes changes too.
Can display *this is not a language

I have been searching the forum and got some pointers,
IC 11 CMOS/RTC
IC10 which was the solution for one member
IC8 VIA
But which one should I change first.....?
My soldering skills are very basic, I have changed IC’s before but I’m not exactly a pro, so don’t want to change too many unnecessarily.

Another question, I have sourced these three ic’s , but IC11 on the pcb is HD146818P, the one I have sourced is HD146818AP, is this Ic ok to use.

Any hints/tips will be appreciated.

Thanks

Dave
Last edited by DaveLecky on Thu Sep 24, 2020 9:09 am, edited 1 time in total.
Electron Plus 3 and plus 1, AP6 and Home made MMFS PP SD interface
Electron Plus 1 Pres AP3/4
Beeb issue 7 with IFEL 16 socket Rom/Ram board
Master 128, BooBip multi OS,IFEL SD card
StrongA RPC, A3020
Atom

User avatar
8271
Posts: 95
Joined: Sun May 24, 2020 1:20 pm
Contact:

Re: Master 128 CMOS Fault

Post by 8271 » Fri Sep 18, 2020 9:35 pm

You might not need to replace the ICs. On all the masters with dodgy CMOS I have been able to fix them by removing the 3 pin header from the MB and soldering a new one in. The original battery (the 3 AA cell type wrapped in cellophane) sometimes leaks and the electrolyte tracks up the wires and corrodes the connector and board.

If you take the header off and replace and reflow the solder around the resistors closest to the header. I would try that before replacing ICs.

Then if you can get to a star prompt you can reconfigure the machine.

*configure mode 7
*configure file 9
*configure lang 12
*configure noboot

You may also need to check the roms are inserted - try

*insert 9
*insert 10
*insert 11
*insert 12
*insert 13
Serial computer hoarder & econetophile
2 x BBC-B, 4 x Master128, Master Viglen, Master Domesday, A310, A4, A5000, RiscPC700 Level 4 Server, RPC_SA233 & RPC_SA200, RiscOS_Pi, Econet & Ethernet

Coeus
Posts: 1892
Joined: Mon Jul 25, 2016 12:05 pm
Contact:

Re: Master 128 CMOS Fault

Post by Coeus » Fri Sep 18, 2020 9:43 pm

You probably do have rubbish in the CMOS RAM but I suspect the fault is not there. It may be with the KB or something else.

User avatar
DaveLecky
Posts: 283
Joined: Mon Jul 08, 2019 7:52 am
Location: Airdrie, Scotland
Contact:

Re: Master 128 CMOS Fault

Post by DaveLecky » Sat Sep 19, 2020 8:16 am

Thanks guys.....I’ll have a look at your suggestions this morning.

Dave
Electron Plus 3 and plus 1, AP6 and Home made MMFS PP SD interface
Electron Plus 1 Pres AP3/4
Beeb issue 7 with IFEL 16 socket Rom/Ram board
Master 128, BooBip multi OS,IFEL SD card
StrongA RPC, A3020
Atom

User avatar
DaveLecky
Posts: 283
Joined: Mon Jul 08, 2019 7:52 am
Location: Airdrie, Scotland
Contact:

Re: Master 128 CMOS Fault

Post by DaveLecky » Sat Sep 19, 2020 6:45 pm

Hi folks,

I’ve checked the battery connections, belled out the tracks......all ok.

I’ve also swapped over the mainboard to my working master 128 and the problem is still present.

Is suppose I’ll have to replace the above IC’s one at a time.... :(

Dave
Electron Plus 3 and plus 1, AP6 and Home made MMFS PP SD interface
Electron Plus 1 Pres AP3/4
Beeb issue 7 with IFEL 16 socket Rom/Ram board
Master 128, BooBip multi OS,IFEL SD card
StrongA RPC, A3020
Atom

User avatar
MJS
Posts: 28
Joined: Sat Aug 01, 2020 12:36 pm
Contact:

Re: Master 128 CMOS Fault

Post by MJS » Sat Sep 19, 2020 7:28 pm

Mine did some of the symptoms you're having (no keyboard, often saw TERMINAL). I went straight for IC8 - the VIA that handles keyboard/sound etc and that was the culprit. I ordered a new, compatible, one here: https://www.ebay.co.uk/itm/164245883607
It's worth putting a socket in if you replace it or just test with an alternative one.
Model B Issue 7
Master128
Gotek, MMC, Pi Tube, MD220 disc drive

User avatar
DaveLecky
Posts: 283
Joined: Mon Jul 08, 2019 7:52 am
Location: Airdrie, Scotland
Contact:

Re: Master 128 CMOS Fault

Post by DaveLecky » Sun Sep 20, 2020 8:27 am

Thanks for the info MJS,

I’ll be checking what I need and ordering bases to suit.

I may try reflowing, just in case I’m lucky, then change them one by one.

Dave
Electron Plus 3 and plus 1, AP6 and Home made MMFS PP SD interface
Electron Plus 1 Pres AP3/4
Beeb issue 7 with IFEL 16 socket Rom/Ram board
Master 128, BooBip multi OS,IFEL SD card
StrongA RPC, A3020
Atom

User avatar
DaveLecky
Posts: 283
Joined: Mon Jul 08, 2019 7:52 am
Location: Airdrie, Scotland
Contact:

Re: Master 128 CMOS Fault

Post by DaveLecky » Wed Sep 23, 2020 7:56 am

SOLVED....

I decided to socket and change IC8 first and BINGO......IT WORKED.

Thanks everyone for your suggestions and help.

Another Master 128 lives to fight another day.

Dave.
Electron Plus 3 and plus 1, AP6 and Home made MMFS PP SD interface
Electron Plus 1 Pres AP3/4
Beeb issue 7 with IFEL 16 socket Rom/Ram board
Master 128, BooBip multi OS,IFEL SD card
StrongA RPC, A3020
Atom

Post Reply

Return to “8-bit acorn hardware”