Tascacm/Teac Portastudio Pwr XFMR

looks like we finally hit rock bottom with this tear-down,

this is a 120 to 11.5 x 2 VAC job, aka, wall wart,

evilbay wants 70 bucks when you can find them, has a weird plug so hard to cross ref,

used one probably will blow up too,

since this thing is screwed and not glued, we can do a 3 day rehab,



where are the specs?    right on the boiler plate, menso,  ;D

hippies out in San Francisco would probably just trash it and watch Manix on the tele,

because they have a life,

man this makes my eyes squint,

has a glass fuse on the circuit board and another thermal hidden in the winds,

these cheap imports get on the fightin side of me,

scatter winding #24 all day will give you the workin man's blues, thats fo sho,

bobbin and fuse ,

that's about as exciting as it gets around here,

and finally the print,

how do i feel about this transformer? better than misery and gin,

it's not love, but it's not bad, if it makes it thru December, i'll be happy,

Tascam 424 MKII?  Just built a power supply (torroid in a metal case with cables) for a client. Uses a DIN plug, not that hard to source.

you got the pinout on the DIN plug?

Hi CJ, can't find my notes at the moment, but it was the MKIII, not MK2.  The DIN pins are paired up, two ground and two each 11.5vac.  There is a photo of how they are grouped at the bottom of this link: https://www.gearslutz.com/board/low-end-theory/816449-modding-tascam-424-mkiii-portastudio.html  Find ground in the unit and put AC on the others!  I used a torroid with dual 12v windings because it's getting rectified and regulated anyhow and either a 5 pin or 3 pin DIN - whichever fit.  Sorry for my crappy memory  :-\

did you bother figure out what was wrong (thermal fuse?).

Those split bobbin transformers are a pretty good way to insure high insulation resistance between primary and secondary.

Do you hi-pot your transformers?

JR

this guy was overheated,

maybe a problem with the Mixer itself

bobbin was melted

both pri and sec were scatter wound with no insl.

we wound  smooth layers and used interlayer insl, no i do not get hi on pot anymore,

DIY hi  potter would be a cool project, can you draw me a quick circuit? 

CJ said:

no i do not get hi on pot anymore,

DIY hi  potter would be a cool project, can you draw me a quick circuit? 

Click to expand...

Here is a DIY rig I whipped up to make (almost) 500V to test the insulation resistance of my outlet tester before I darkened UL's door. They require 100M @ 500V.

The rig is simple, 4 identical transformers with all the secondaries connected in parallel. 120 VAC is fed into the first primary, and the other three primaries are stacked in series, making an auto-former with roughly 4x mains voltage (confirmed)

To measure my 100M input resistor I used a VOM in current mode, and calculated backwards to impute the resistance. Using this Rube Goldberg test rig, I estimated my 100M input resistor was only delivering about 50M of insulation. 

I did not have much faith in my test rig, but luckily a friend had a megger laying around that he wasn't using and lent it to me.

Surprisingly the fancy fluke tester confirmed my crude measured short fall in insulation resistance.

Once I trusted the measurement data I dug deeper to discover why my 100M resistors were not behaving and got a little quick education about SMD resistor voltage.

Small SMD resistors are only rated for 50-100V.  At 500V stuff happens. To get 600V rated SMD resistors involves going up to 2012 or larger smd packages. 

JR

PS: I am not comfortable with 500V diy, but if careful you should be OK. I put a small fuse between the first secondary and the other three, but it could still easily kill me long before that fuse blew. 

here is the DIN pinout for this Tascam supply,

and we had a color code wrong on the print which has been fixed, thanks to the Gearslutz link,