H7826 PSU, No Signal On Transformer Outputs

Brent Hilpert bhilpert at shaw.ca
Mon Nov 6 13:44:10 CST 2017

On 2017-Nov-05, at 9:14 AM, Rob Jarratt via cctalk wrote:
> I have moved on with the work on the H7826 PSU in the TURBOchannel Extender.
> However I have found that there appears to be no signal at all on the output
> windings of the transformer. I have posted all the details of what I have
> been doing here
> http://robs-old-computers.com/2017/11/05/repair-progress-on-the-h7826-power-
> supply/, and I would welcome any suggestions as to what might cause this?

"I then checked the primary side of the transformer and I could see a signal."

You don't describe the nature of the signal, but regardless, seeing a voltage signal at some point on the primary
is not a guarantee that current is flowing through the primary, current being necessary for induction and getting anything out of the secondaries.

It depends on the primary side driver arrangement, (going by the H7861 schematic DEC used some funky arrangements, is the 7826 schematic available?),
For example you might see a voltage signal from the high-side driver, but the low-side driver could be faulty.

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