AVO Digital System DS109 with Multimeter Module MM110

[factory]

I've posted a few pictures of these in the AVO multimeter survey thread a while back, but they really deserve a thread of their own.

I now have two of these early digital AVO multimeters, they comprise of a digital system mainframe type D.S.109 with a multimeter module type M.M.110, the multimeter modules both have the optional AC board fitted AC.111.
There is an advert in the May 1969 wireless world here (page 3/A1); https://worldradiohistory.com/UK/Wir...ld-1969-05.pdf
Other modules were apparently available for using the system as a timer counter and a low frequency generator, but I can't find any other information about those.

The first mainframe has an early serial number of PP003, but the multimeter module is a bit later serial no. 205, this module also has a redesigned mixer/trigger board (more on that later). I suspect this originally had a LF Gen module fitted, as the plug is marked.
It was completely dead when it arrived last year, but re-soldering some bad joints on the +/-12V supply PCB has got it going again in manual mode, internal trigger was not working, the internal Muirhead reference cell is almost completely dead too.


The second mainframe is serial no. 239 with multimeter module serial no. 249, this has the original single sided mixer/trigger board.
I bought this one locally in October last year, it was upside down when I collected it, the reference cell wasn't completely dead this time, it was down to around 960mV from the 1.01925V on the Muirhead paperwork inside (this has since fully recovered). This one was only displaying zeros when tested.


Since then I have retrieved the first one from storage, to work out which parts are faulty and have started repairs.

David

[pmmunro]

David,

This a very interesting digital instrument system. In 1969 it would have been a very advanced design with considerable potential in a market where no-one could be certain how electronic instrumentation of the type might develop.

It also came around the time that AVO was acquired by the Thorn Group. I don't know much about Thorn but in a much later discussion with one of AVO's senior staff who was there at the time, I was told that Jules Thorn was in no mood to indulge anyone after the take over and was principally interested in cutting costs. One consequence was the redesign of the Model 8 multimeter to produce the Mk IV version, possibly the least sucessful of all that series.

I would like to suggest that this post might usefully be transferred to the Avo Multimeter Survey thread where I would expect there would be great interest and it would possibly produce many informative comments.

PMM

[ChristianFletcher]

Ahhhh. I didn’t know they existed. Now I want one!

[factory]

Originally Posted by pmmunro

David,

This a very interesting digital instrument system. In 1969 it would have been a very advanced design with considerable potential in a market where no-one could be certain how electronic instrumentation of the type might develop.

PMM

There are a couple of IC's in the input boards in amongst the transistors & other discrete components. The mixer/trigger card and the display counting section use a lot of DTL logic, but only two types of DTL. Oddly the highest count for the display is only 1999, the symbol tube does have a 1 inside but they choose not to use it.
I wouldn't be surprised if the development of this system went back a little further than 1969.

I've already posted both of these in the survey thread, there was a couple of replies including from Andy at Megger, sadly there isn't much in the archives about this apart from a few adverts and a drawing. This thread will be a more detailed look at all the parts & repair that would be lost amongst the survey thread.

Originally Posted by ChristianFletcher

Ahhhh. I didn’t know they existed. Now I want one!

Keep a lookout & hopefully you will find another, the first one was available for a very long time before I rescued it, I was surprised to find a second a few months later.
But do note that no service information exists (as far as I know).

David

[ChristianFletcher]

Thanks David good luck

[Dekatron]

Here's the unobtainable Operation and Maintenance manual for the DS109 & MM110 units!

Put all files in the same folder and rename the files as below:

"The AVO Digital System - DS109 and MM110 - OCR.z01.zip" to "The AVO Digital System - DS109 and MM110 - OCR.z01"

"The AVO Digital System - DS109 and MM110 - OCR.z02.zip" to "The AVO Digital System - DS109 and MM110 - OCR.z02"

"The AVO Digital System - DS109 and MM110 - OCR.z03.zip" to "The AVO Digital System - DS109 and MM110 - OCR.z03"

"The AVO Digital System - DS109 and MM110 - OCR.z04.zip" to "The AVO Digital System - DS109 and MM110 - OCR.z04"

"The AVO Digital System - DS109 and MM110 - OCR.z05.zip" to "The AVO Digital System - DS109 and MM110 - OCR.z05" (found in next post)

and the use Winzip to unzip the split archive into "The AVO Digital System - DS109 and MM110 - OCR.pdf"

[Dekatron]

Here's the last file!

[factory]

Thank you very much for scanning those manuals, I've managed to fix most of the faults without a manual, but the second analogue to digital board in one of them is proving more tricky with an intermittent fault, hopefully I'll be able to track it down now.

David

[Dekatron]

Thanks, I hope they will be of some use finding that intermittent error you have.

If possible please post more photos of the insides and of the circuit boards as that might help other people who own one of these if they need to repair them.

[Vintage_RC]

I joined Aladdin Components back in 1969 as a young recently graduated R&D engineer to work in the lab of their new Aladdin Instruments division. As a new division all the test equipment was brand new and we had an AVO DS109. It needed regular calibration against the internal reference cell, this had to be done for both positive and negative voltages. At the time it seemed a very advanced piece of equipment but of course today you can buy a multi meter which can do all of this for a few pounds. It has always intrigued me how this piece of AVO equipment seemed to vanish into obscurity. I will be following this thread with interest.

[Vintage_RC]

I'm having problems opening the zip archives, anyone else tried opening and viewing them?

[factory]

Yes you maybe be able to buy a DMM for a few pounds, but it won't have the higher voltage ranges that the MM110 has, it's supposed to be usable to 2000V AC or DC, not quite as high as the analogue AVO's it was presumably meant to replace (but never did).

David

Edit: You have to right click and save each file to the same folder, then rename to remove the .zip from the five files (z01 to Z05) as mentioned, before trying to open & combine them.

[factory]

Here are some pictures of the DS109 mainframe, as the module has the power switch you can't power up the display section without one fitted, also mains voltage is present on two pins of the right hand connector, something to be aware of if working on one of these. I had to trace this out as the first one didn't work at all until I had found the mains fuse in the MM110 module was blown.


An overview of the inside of the DS109 mainframe (sn. PP003) you will notice this early one has no markings on any of the boards, the module that came with it is later and does have board markings.


Power supply section that provides a regulated +6V supply to the DTL logic IC's in both the display section & an extra (fused) feed to the module and +250V unregulated for the display readouts & decimal point indicators.


The 1MHz crystal frequency reference is on the last display board, as I already mentioned the fourth readout only displays 0 or 1 and the symbol readout display the +/-polarity and X for overrange (the 1 is not used).


David

[gingpeakin]

I've got one of these in storage but I'm struggling to open the zipped files. I remember now why I hate winzip and most of the free alternatives. Can anyone point me in the right direction - I think I followed the instruction correctly but I keep getting error messages along the lines of 'does not appear to be a valid archive'

Ging

[factory]

The decade divider board, all the IC's are Mullard FCJ 101 JK flip flops to divide the 1MHz refencence input in six divide-by-ten stages from 100kHz down to 1Hz.


There are three identical display boards using more FCJ 101 IC's for the dividers and diodes to decode the BCD output from those for the decimal readout, the divide-by-ten output goes to the next readout card.


Need to take some pictures of boards from the later DS109.

David

[factory]

Originally Posted by gingpeakin

I've got one of these in storage but I'm struggling to open the zipped files. I remember now why I hate winzip and most of the free alternatives. Can anyone point me in the right direction - I think I followed the instruction correctly but I keep getting error messages along the lines of 'does not appear to be a valid archive'

Ging

Well that's at least four of these AVO digital systems that have survived.

I don't have Winzip installed as far as I know, once all the files were in the same folder & renamed, I used right click and extract all on the remaining zip file (I'm using Windows 10).

David

[pmmunro]

David,

Many thanks for taking the trouble to post all this information. The photographs show a very high standard of construction which would have determined the final price. Had a later version been made and sales predictions justified it, that later version would probably have used construction techniques more suited to volume production.

I don't think this system would have been intended to replace the conventional multimeters, at least certainly not at the time of the DS109 being introduced.

In the late 1960s the British instrument market was still a very conservative one. AVO produced several designs which were more modern than the familiar Models 7, 8 and 40 but they do not seem to have been widely offered on the home market. For example, the Model 10, and the Models 14, 15, 16, 20/21 and EA113.

PMM

[Dekatron]

Thanks for the photos!

[TonyDuell]

I can't extract that archive either

I'm still running Windows 8.1 and the program that is trying to make sense of it seems to be called 7-Zip. It claims it is not a valid archive.

Is there any way some kind person could put a single file (either a .pdf or a normal .zip) somewhere to download, please

[Dekatron]

I just downloaded them, se picture 1, then renamed them, se picture 2, and then just doubleclicked the file named "The AVO Digital System - DS109 and MM110 - OCR.zip" and Windows 10 offered to unpack them, but I could also use Winzip, 7-Zip and WinRAR to unzip the archive without problem - all running on Windows 10, so the archive is not damaged, see picture 3.

Maybe your operating system or zip-programs aren't compatible.