Fitting a BT Viscount MF circuit board into a Viscount pulse dialling phone
 

Hi. I recently bought a BT Viscount pulse dialling telephone in very nice condition and was considering replacing the circuit board with the MF circuit board from another Viscount.

Question is, would the MF circuit board from the more recent Viscount fit inside the body of the older Viscount and would the MF/LD pulse switches underneath prevent the circuit board from sitting properly inside the case of the older Viscount?

Thanks for your help.

Re: Fitting a BT Viscount MF circuit board into a Viscount pulse dialling phone
 

Hello, and welcome to the forum! The only Viscounts I have seen have the switches for LD or MF and TB, sat in a recess behind a clip-on plastic cover on the LHS as looking at the base of the telephone.

Has your model got this recess in the case and two holes where the switches go? If so, there's a chance the board will fit.

Re: Fitting a BT Viscount MF circuit board into a Viscount pulse dialling phone
 

Thank you. Yes, I can see 2 recesses. The underside of my Viscount 9521AR looks exactly the same as a photo of an MF version I've seen. Looking through the holes I can see the back of the brown circuit board, nothing else. Strange that BT would design the body to accommodate MF switches but then fit a Pulse only circuit board.

I can't see any screws underneath so it looks like the case needs to be unclipped to open it up.

Re: Fitting a BT Viscount MF circuit board into a Viscount pulse dialling phone
 

Just noticed the single screw underneath where the handset goes.

It seems to come off easiest if it's held upright and then gradually pulled away from the base from left to right, pushing the hook switch in as you move across.

Re: Fitting a BT Viscount MF circuit board into a Viscount pulse dialling phone
 

What will you do about the * and # keys? Does your LD-only phone have holes for them with 'blank' (non-functioning) buttons in there?

You beat me to it about the screw beneath the handset rest. The telephones were made by ST&C and would be made with economy and versatility in mind. It's interesting to note that the 'InDEX' digital PABX telephone system used instruments with cases and handsets that were obviously based upon the Viscount, but not quite the same.

Re: Fitting a BT Viscount MF circuit board into a Viscount pulse dialling phone
 

Here's what I mean... Viscount MF / LD from 1980s against an InDEX DT3, late 1990s.

Re: Fitting a BT Viscount MF circuit board into a Viscount pulse dialling phone
 

I've seen those before and noticed the similarity.

But I have to say that the cleaner lines of the ~15 year older original get my vote. The InDEX looks cheap and fussy in comparison.

Re: Fitting a BT Viscount MF circuit board into a Viscount pulse dialling phone
 

I agree, Nick. The InDEX system worked very well and the DT1 instruments (later provided by Avaya) were great. But the basic DT3 instruments, as shown, were prone to failure. Not due to the complexities of the circuitry within, but simple things like mic failure, switch failure and poor cordage.

I had a Viscount for years (not the one shown) and ultimately it suffered from keypad intermittency, but this was rectified by cleaning. The weakest point was severe discolouration. A nice telephone all the same. I still have it so may try dunking the case in 'Oxy Action' in sunlight (a cheap 'Retrobright' process).

Re: Fitting a BT Viscount MF circuit board into a Viscount pulse dialling phone
 

Are you sure that your Viscount is a 9521R or 9525AR? Telephones UK lists them as LD/TD switchable models.

I wonder if the board has been replaced with an LD board at some point in the past.

The 9521AR has the same number of buttons as the MF version though * and # are replace with buttons that have . and .. on them.

This is the thing I was worried about. The phone I have is new/old stock so I was originally reluctant to fit an old circuit board into it just in case the keypad membrane proved un-reliable.

I was hoping the website was correct though the manual confirms that it is LD/Pulse only.