Osborne Vixen - Zenith 7" display t-shooting issues

drlegendre . drlegendre at gmail.com
Mon Nov 3 21:38:50 CST 2014

Chuck, my friend...

On Mon, Nov 3, 2014 at 3:59 PM, Chuck Guzis <cclist at sydex.com> wrote:

> I've got the service manual to the Zenith DT2 display (includes a linear
> PSU); dated 1979 and identified as part of the D12 series of monitors.
> The HOT is a Zenith 121-1039, which, according to NTE is replaceable by
> NTE 379.
> http://www.vetco.net/catalog/product_info.php?
> manufacturers_id=14&products_id=3504
> Dunno if that helps or not.
You may have cracked one of the tougher nuts, sir! Now check this out..

When you quoted the HOT for the DT12 chassis as part # 121-1039, that 1039
seemed an awful lot like 1070 to me. So on a hunch, I punched "zenith
121-0170" into Google - and guess what?

The Zenith 121-1070 is in fact a high voltage, high-speed switching
transistor. As mentioned previously, it's an in-house Zenith part number,
which probably includes several different but similar devices that all fall
within the same specs. Per the manufacturer, it is suitable (among other
apps) for deflection circuits. A little more searching (eBay helped) turned
up that it crosses to the NTE 379 - just as does the HOT in your Zenith

I think it's safe to say that the HOT in the Osborne Vixen Zenith display
is a "Zenith 121-1070".. which apparently subs to the same NTE / ECG 379
part. Very slick..

Data sheet for the 121-1070 / NTE 379 calls out a beta of 8-10 min. and
30-40 max. So that leads me to believe that the original 1070 HOT may, in
fact, be OK - and the issue is to be found elsewhere in the circuit. It's
not a for-sure, as the part might be misbehaving under actual circuit
conditions - but at least I have some confidence that we know what it's
supposed to be. Thank you..


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