Dim display - UK Vintage Radio Repair and Restoration Discussion Forum

Linnovice · 24th Aug 2016, 7:00 pm

I'm not sure if this eligible for this forum but I've just bought a Tascam DA-20 MkII DAT machine. It's my first venture into this medium and I'm quite impressed with the quality of the sound. My only problem is with the display. It's very dim, almost invisible from a couple of feet away. Is there any way that it can be increased. There are no controls on the facia (that I can see) so I'm wondering if there is an adjustment pot inside.
Mike

peterpiper · 24th Aug 2016, 7:28 pm

Hi Mike, from looking at pictures of the DA20 the display is vacuum fluorescent display, VFD. they work by having a heated filament and the display characters are fed by about 100v DC. If cleaning the front face of the display (carefully) doesn't help, you could try increasing the supply to the filament slightly. I did this recently to a Quad 44 tuner that had been sitting in a BBC rack all its life and was getting a bit dull. Very effective and OK after a year. I don't know how Tascam feeds the filament, if its DC it should be easy to increase it. Some makers use AC from a low voltage winding on the tranny making it harder to modify. All is not lost, you could modify the feed to DC taken from another supply line.

Peter

vidjoman · 24th Aug 2016, 8:18 pm

I've come across several VFD displays in low voltage equipment (video recorders for example) where the high voltage is derived from a small oscillator and capacitors are usually the problem. I suspect increasing the heater voltage is a bodge rather than proper fault finding repair and may well lead to premature failure of the display.

Sideband · 24th Aug 2016, 8:24 pm

Quote:

Originally Posted by vidjoman

I've come across several VFD displays in low voltage equipment (video recorders for example) where the high voltage is derived from a small oscillator and capacitors are usually the problem.

Yes...agree with this. Very common in the days of VFD's and video recorders. Some manufacturers provided a small 'kit' consisting of several electrolytics and possibly even a couple of resistors to facilitate repair of the oscillator/voltage doubler...or whatever else was used to provide the HT supply.

I seem to recall that Akai were particularly prone but after a couple of cap changes, the display was good as new.

Michael Maurice · 25th Aug 2016, 9:22 am

I agree with Sideband and Vidjoman, make sure you use good quality low ESR capacitors rated at 105 degrees.

I get my capacitors from RS and usually get Nichicons or Panasoniics

Linnovice · 25th Aug 2016, 9:28 pm

Ok guys, thanks for the suggestions. I will have a look inside and try to fathom out which caps need changing. I've had a look at the SM on line but it's a bad copy and slightly distorted.
I too get my caps from RS and a very good service they offer. I'm in the process of totally recapping a Revox B77 MkII HS. A good learning curve. Perhaps the Tascam won't present too much of a challenge . . . hopefully.

24th Aug 2016, 7:00 pm	#1
Linnovice Hexode Join Date: Jun 2014 Location: Chelmsford, Essex, UK Posts: 386	Dim display I'm not sure if this eligible for this forum but I've just bought a Tascam DA-20 MkII DAT machine. It's my first venture into this medium and I'm quite impressed with the quality of the sound. My only problem is with the display. It's very dim, almost invisible from a couple of feet away. Is there any way that it can be increased. There are no controls on the facia (that I can see) so I'm wondering if there is an adjustment pot inside. Mike __________________ Small Scotch, New Aids and Happy Ears

24th Aug 2016, 7:28 pm	#2
peterpiper Tetrode Join Date: Jul 2016 Location: Renfrew, Renfrewshire, UK. Posts: 93	Re: Dim display Hi Mike, from looking at pictures of the DA20 the display is vacuum fluorescent display, VFD. they work by having a heated filament and the display characters are fed by about 100v DC. If cleaning the front face of the display (carefully) doesn't help, you could try increasing the supply to the filament slightly. I did this recently to a Quad 44 tuner that had been sitting in a BBC rack all its life and was getting a bit dull. Very effective and OK after a year. I don't know how Tascam feeds the filament, if its DC it should be easy to increase it. Some makers use AC from a low voltage winding on the tranny making it harder to modify. All is not lost, you could modify the feed to DC taken from another supply line. Peter

24th Aug 2016, 8:18 pm	#3
vidjoman Dekatron Join Date: Jun 2013 Location: East Sussex, UK. Posts: 3,326	Re: Dim display I've come across several VFD displays in low voltage equipment (video recorders for example) where the high voltage is derived from a small oscillator and capacitors are usually the problem. I suspect increasing the heater voltage is a bodge rather than proper fault finding repair and may well lead to premature failure of the display.

25th Aug 2016, 9:22 am	#5
Michael Maurice Moderator Join Date: Feb 2006 Location: Wembley, Middlesex Posts: 7,225	Re: Dim display I agree with Sideband and Vidjoman, make sure you use good quality low ESR capacitors rated at 105 degrees. I get my capacitors from RS and usually get Nichicons or Panasoniics __________________ Forum Moderator http://www.michaelmauricerepairs.co.uk/

25th Aug 2016, 9:28 pm	#6
Linnovice Hexode Join Date: Jun 2014 Location: Chelmsford, Essex, UK Posts: 386	Re: Dim display Ok guys, thanks for the suggestions. I will have a look inside and try to fathom out which caps need changing. I've had a look at the SM on line but it's a bad copy and slightly distorted. I too get my caps from RS and a very good service they offer. I'm in the process of totally recapping a Revox B77 MkII HS. A good learning curve. Perhaps the Tascam won't present too much of a challenge . . . hopefully. __________________ Small Scotch, New Aids and Happy Ears