Inverter Transformer 2200 Series Oscilloscopes, primary resistance

[THM60]

Hi,

I suspect the primary winding of the Inverter Transformer in my Tek 2230 is shorted. When measuring its resistance between terminals 1 & 2 with my DVM, I find 0,7R. What do you think ?

Part number is 120-1439-01 (photo attached). In the worst situation, is this transformer on the unobtainable parts list ?

Thanks !

[TheMG]

Not impossible but rather unlikely.

A low DC resistance is normal for such transformers. Since they operate at high frequencies the number of turns is small when compared to a 50/60Hz transformer, so the DC resistance being less than 1 ohm is actually not unexpected.

[WattsThat]

<1 ohm is expected, not shorted. Do waveforms 42/43/44/45 match what is shown in the service manual?

[THM60]

Thanks for responses.

<1 ohm is expected, not shorted. Do waveforms 42/43/44/45 match what is shown in the service manual?

I can't check that for the time being as the fuse keeps blowing. Two of the three neon bulbs flash (DS858,DS870) and fan shudders one or two times but scope doesn't turn on. 

[jonpaul]

get service manual follow PSU tests and troubleshooting flow chart

j

[floobydust]

From my notes, Pre-regulator transformer T906 (120-1439-01) readings:
T906 1,2  3.50mH 2.05 ohms Primary Winding
T906 4,5  3.75mH 1.57 ohms Reset Winding
T906 9,10 4.50uH 0.22 ohms Tank Winding
T906 6,7  452uH  2.00 ohms Aux Winding
another person's measurements: https://www.eevblog.com/forum/repair/tektronix-2213a-scope-exploding-power-supplies!/msg864495/#msg864495

I say don't run the scope if DS870 (CRT cathode-grid protection neon) is lit steady. You can see polarity by which pole (-) is lit.
I'd suspect the -2kV rail, it might have a heavy load (cooked focus divider resistors) or that output on the HV multiplier (rectifier) has failed where it outputs AC.

[THM60]

Thank you so much, I'm going to investigate further with the figures you indicated in hand

[marcumr]

Hello.

Check out that yellow tantalum, mine had a hole in the bottom and shorted out

[THM60]

Hi again Floodybust,

I've removed T906 from the main board (pain in the back) for measurements. Inductance and resistance as follow.