I'm new to this group. I'm a BS EE who's serviced electronic equipment most
of his life, so don't hesitate to get as technical as you like.

When I reviewed the NAD MR-20 for Stereophile 20+ years ago, I was so
impressed I bought one. It's given me yeoman service; I suspect it has 20K
hours on it. Until now, the only problem was some bad electrolytics on the
video driver board.

The current problem is intermittent loss of brightness accompanied by loss
of focus. Adjusting the Screen and Focus controls improved things, and
removing the back greatly reduced the frequency of the problem (presumably
because the set runs cooler).

This might be the CRT, but I suspect it's the HV rectifier. (Tapping the
neck of the CRT has no effect, but that's not a definitive test.)

The problem is that the HV rectifier appears to be potted within the flyback
transformer assembly. The transformer is no longer available (nor is the
CRT). Before I yank the transformer (it's not easily removed), I need to
know whether the HV rectifier is accessible. And, of course, I'd appreciate
_any_ thoughts on servicing this set.

Thanks in advance.

On Sat, 1 Sep 2007 05:46:23 -0700, "William Sommerwerck"
wrote:

I'm new to this group. I'm a BS EE who's serviced electronic equipment most
of his life, so don't hesitate to get as technical as you like.

When I reviewed the NAD MR-20 for Stereophile 20+ years ago, I was so
impressed I bought one. It's given me yeoman service; I suspect it has 20K
hours on it. Until now, the only problem was some bad electrolytics on the
video driver board.

The current problem is intermittent loss of brightness accompanied by loss
of focus. Adjusting the Screen and Focus controls improved things, and
removing the back greatly reduced the frequency of the problem (presumably
because the set runs cooler).

This might be the CRT, but I suspect it's the HV rectifier. (Tapping the
neck of the CRT has no effect, but that's not a definitive test.)

The problem is that the HV rectifier appears to be potted within the flyback
transformer assembly. The transformer is no longer available (nor is the
CRT). Before I yank the transformer (it's not easily removed), I need to
know whether the HV rectifier is accessible. And, of course, I'd appreciate
_any_ thoughts on servicing this set.

Thanks in advance.



The HV rectifier is in the flyback assembly. As a side note, I
purchased the last flyback NAD had in stock about 7 years ago. It was
the second most likely part to fail. The first being the electrolytic
capacitor on the crt board. This set was actually made by Sampo but I
don't believe any set made under their name used this flyback. Chuck

"Chuck" wrote in message
...

The HV rectifier is in the flyback assembly.

Thanks for the info. I won't be rushing to remove the flyback.


I purchased the last flyback NAD had in stock about 7 years ago.
It was the second most-likely part to fail...

If only I'd known... grin


...the first being the electrolytic capacitor on the CRT board.

I assume you mean C13. Electrolytics are cheap, so I ought to replace a
bunch.


This set was actually made by Sampo...

NAD's idea was, instead of designing a new color TV from scratch, they'd
pick a "good" existing model and improve it. The Sampo was their choice, but
it required more upgrading than they expected.