Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
  #1   Report Post  
Posted to sci.electronics.repair
external usenet poster
 
Posts: 5
Default NAD317 Strange Oscillating PSU?

Hello All,
I hope someone may help me with fixing this NAD317 integrated
amplifier made in 1997.
The owner reported strange distortion only at low levels of output on
both channels.
Hook up a 'scope & feeding in a 1kHz sine wave shows intermittent high
frequency oscillation distorting the waveform. You can see the traces
on the link below:

http://personales.ya.com/cannet/

My first suspicion is the PSU electrolytic caps (6 off 4700uF 63V & 4
off 220uF 160V), when I tap around them sometimes the fault goes away
if present. Similarly I can sometimes cause the fault by tapping them.
But strangely I can see no sign of the oscillations on the power
supply rails to either pre or power amp (the distortion is present at
the pre amp output). Also strange is that sometimes just passing my
hand over the PSU board can cause or cure the fault. Perhaps this
could be a dry joint also?

Any tips on trouble shooting this are welcome.
Best regards,
Greg.
  #2   Report Post  
Posted to sci.electronics.repair
external usenet poster
 
Posts: 1,220
Default NAD317 Strange Oscillating PSU?

Greg wrote in message
...
Hello All,
I hope someone may help me with fixing this NAD317 integrated
amplifier made in 1997.
The owner reported strange distortion only at low levels of output on
both channels.
Hook up a 'scope & feeding in a 1kHz sine wave shows intermittent high
frequency oscillation distorting the waveform. You can see the traces
on the link below:

http://personales.ya.com/cannet/

My first suspicion is the PSU electrolytic caps (6 off 4700uF 63V & 4
off 220uF 160V), when I tap around them sometimes the fault goes away
if present. Similarly I can sometimes cause the fault by tapping them.
But strangely I can see no sign of the oscillations on the power
supply rails to either pre or power amp (the distortion is present at
the pre amp output). Also strange is that sometimes just passing my
hand over the PSU board can cause or cure the fault. Perhaps this
could be a dry joint also?

Any tips on trouble shooting this are welcome.
Best regards,
Greg.


About what frequency is the hf oscillation?
Can you make it change frequency by bringing your finger near anything.?
loose/broken ground connection somewhere between ps/prea/pa?


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/


  #3   Report Post  
Posted to sci.electronics.repair
bz bz is offline
external usenet poster
 
Posts: 314
Default NAD317 Strange Oscillating PSU?

"N Cook" wrote in :

Greg wrote in message
...
Hello All,
I hope someone may help me with fixing this NAD317 integrated
amplifier made in 1997.
The owner reported strange distortion only at low levels of output on
both channels.
Hook up a 'scope & feeding in a 1kHz sine wave shows intermittent high
frequency oscillation distorting the waveform. You can see the traces
on the link below:

http://personales.ya.com/cannet/

My first suspicion is the PSU electrolytic caps (6 off 4700uF 63V & 4
off 220uF 160V), when I tap around them sometimes the fault goes away
if present. Similarly I can sometimes cause the fault by tapping them.
But strangely I can see no sign of the oscillations on the power
supply rails to either pre or power amp (the distortion is present at
the pre amp output). Also strange is that sometimes just passing my
hand over the PSU board can cause or cure the fault. Perhaps this
could be a dry joint also?

Any tips on trouble shooting this are welcome.
Best regards,
Greg.



The fact that it is a positive going oscillation on positive peaks and a
negative going oscillation on the negative peaks rather than going above
and below the 1 kHz signal should be some kind of a clue but I am not sure
exactly what it is telling us.
The oscillation looks like it is 15 or 20 kHz.

Could you have a bad ground connection somewhere?

Have you tried looking with your scope at the ground for the preamp and the
ground for the PA, using the PS ground as your reference?





--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

remove ch100-5 to avoid spam trap
  #4   Report Post  
Posted to sci.electronics.repair
external usenet poster
 
Posts: 259
Default NAD317 Strange Oscillating PSU?

I would start by taking an ESR meter and going through every cap in the
amplifier.

--

JANA
_____


"Greg" wrote in message
...
Hello All,
I hope someone may help me with fixing this NAD317 integrated
amplifier made in 1997.
The owner reported strange distortion only at low levels of output on
both channels.
Hook up a 'scope & feeding in a 1kHz sine wave shows intermittent high
frequency oscillation distorting the waveform. You can see the traces
on the link below:

http://personales.ya.com/cannet/

My first suspicion is the PSU electrolytic caps (6 off 4700uF 63V & 4
off 220uF 160V), when I tap around them sometimes the fault goes away
if present. Similarly I can sometimes cause the fault by tapping them.
But strangely I can see no sign of the oscillations on the power
supply rails to either pre or power amp (the distortion is present at
the pre amp output). Also strange is that sometimes just passing my
hand over the PSU board can cause or cure the fault. Perhaps this
could be a dry joint also?

Any tips on trouble shooting this are welcome.
Best regards,
Greg.


  #5   Report Post  
Posted to sci.electronics.repair
external usenet poster
 
Posts: 5
Default NAD317 Strange Oscillating PSU?

Thanks for the tips guys, Nigel I will check the grounds as you
suggest, Jana - I have ordered an ESR meter & will try that. Here in
southern Spain I have seen many dried out caps & this meter will help.
Best regards, Greg.


  #6   Report Post  
Posted to sci.electronics.repair
external usenet poster
 
Posts: 81
Default NAD317 Strange Oscillating PSU?

Greg wrote:
Hello All,
I hope someone may help me with fixing this NAD317 integrated
amplifier made in 1997.
The owner reported strange distortion only at low levels of output on
both channels.
Hook up a 'scope & feeding in a 1kHz sine wave shows intermittent high
frequency oscillation distorting the waveform. You can see the traces
on the link below:

http://personales.ya.com/cannet/

My first suspicion is the PSU electrolytic caps (6 off 4700uF 63V & 4
off 220uF 160V), when I tap around them sometimes the fault goes away
if present. Similarly I can sometimes cause the fault by tapping them.
But strangely I can see no sign of the oscillations on the power
supply rails to either pre or power amp (the distortion is present at
the pre amp output). Also strange is that sometimes just passing my
hand over the PSU board can cause or cure the fault. Perhaps this
could be a dry joint also?

Any tips on trouble shooting this are welcome.
Best regards,
Greg.

Greg,

There is a NAD service bulletin that might relate to your problem:

"PROBLEM: a distortion is audible, sometimes after a few hours use, or
one channel will play not as loud as the other."

"Cause: There is a bad contact between the power supply PCB and the
power amplifier board caused by a bad contact inside the connector of
the screened (shielded) cable."

"SOLUTION: Remove the two pin plug and solder the screened cable
directly to the PCB. It is advisable to perform this modification when
the unit comes in for any service."

"PRODUCTION: This modification will be implemented in production, there
is no serial number information known at this moment."

This service note is from 1996. It might even be an audio cable that
carries the ground that is the problem, so I'd suggest checking all of
the shielded cables going to the amp boards. Sorry, I don't have
connector number info.

Regards,
Tim Schwartz
Bristol Electronics

P.S. This also confirms what Nigel Cook and "BZ" thought. I doubt that
the capacitors are the issue.


  #7   Report Post  
Posted to sci.electronics.repair
external usenet poster
 
Posts: 519
Default NAD317 Strange Oscillating PSU?

Tim Schwartz wrote:
There is a NAD service bulletin that might relate to your problem:

"PROBLEM: a distortion is audible, sometimes after a few hours use, or
one channel will play not as loud as the other."

"Cause: There is a bad contact between the power supply PCB and the
power amplifier board caused by a bad contact inside the connector of
the screened (shielded) cable."

"SOLUTION: Remove the two pin plug and solder the screened cable
directly to the PCB. It is advisable to perform this modification when
the unit comes in for any service."


But make sure you still use the shielded cable to run power through.
Great work, NAD.

--
Iran tells us what the mainstream media won't:
"A new opinion poll suggests that over 54 percent of Americans do not trust
mainstream media and consider news websites more reliable."
http://www.presstv.ir/detail.aspx?id=46837&sectionid=3510203
  #8   Report Post  
Posted to sci.electronics.repair
external usenet poster
 
Posts: 5
Default NAD317 Strange Oscillating PSU?

Hi Tim,
Thanks for the info. This amp has been modified I guess at the
factory as it was made mid 1997. The wires were soldered to the board
& covered with hot melt glue which I think is a bad thing. I have
removed both input screened cables & replaced as a precaution.
Sadly it has made no difference to the problem.
I am checking the ground connections but I still suspect the design of
the PSU is inherently unstable. I can induce the fault by switching on
my heat gun & holding over the PSU board. I was trying to see if the
problem is heat related but it seems not.

Clifto - I don't understand your comment. I have replaced the screened
cables as described above but are you suggesting the power leads need
screening too?

Best regards,
Greg.
  #9   Report Post  
Posted to sci.electronics.repair
external usenet poster
 
Posts: 211
Default NAD317 Strange Oscillating PSU?


"Greg" wrote in message
...
Hi Tim,
Thanks for the info. This amp has been modified I guess at the
factory as it was made mid 1997. The wires were soldered to the board
& covered with hot melt glue which I think is a bad thing. I have
removed both input screened cables & replaced as a precaution.
Sadly it has made no difference to the problem.
I am checking the ground connections but I still suspect the design of
the PSU is inherently unstable. I can induce the fault by switching on
my heat gun & holding over the PSU board. I was trying to see if the
problem is heat related but it seems not.

Clifto - I don't understand your comment. I have replaced the screened
cables as described above but are you suggesting the power leads need
screening too?

Best regards,
Greg.


If the glue is at all browned, remove it.

Mark Z.


  #10   Report Post  
Posted to sci.electronics.repair
external usenet poster
 
Posts: 519
Default NAD317 Strange Oscillating PSU?

"Greg" wrote in message
...
Hi Tim,
Thanks for the info. This amp has been modified I guess at the
factory as it was made mid 1997. The wires were soldered to the board
& covered with hot melt glue which I think is a bad thing. I have
removed both input screened cables & replaced as a precaution.
Sadly it has made no difference to the problem.
I am checking the ground connections but I still suspect the design of
the PSU is inherently unstable. I can induce the fault by switching on
my heat gun & holding over the PSU board. I was trying to see if the
problem is heat related but it seems not.

Clifto - I don't understand your comment. I have replaced the screened
cables as described above but are you suggesting the power leads need
screening too?


(piggybacking - somehow the original never got here)

I just have objections in principle to running power through a shield braid
inside an electronic unit. It seems a cheap way to save a penny. I myself
would add a 16-gauge wire for power (ground) connection.

--
Iran tells us what the mainstream media won't:
"A new opinion poll suggests that over 54 percent of Americans do not trust
mainstream media and consider news websites more reliable."
http://www.presstv.ir/detail.aspx?id=46837&sectionid=3510203


  #11   Report Post  
Posted to sci.electronics.repair
external usenet poster
 
Posts: 81
Default NAD317 Strange Oscillating PSU? More thoughts...

Greg wrote:
Hello All,
I hope someone may help me with fixing this NAD317 integrated
amplifier made in 1997.
The owner reported strange distortion only at low levels of output on
both channels.
Hook up a 'scope & feeding in a 1kHz sine wave shows intermittent high
frequency oscillation distorting the waveform. You can see the traces
on the link below:

http://personales.ya.com/cannet/

My first suspicion is the PSU electrolytic caps (6 off 4700uF 63V & 4
off 220uF 160V), when I tap around them sometimes the fault goes away
if present. Similarly I can sometimes cause the fault by tapping them.
But strangely I can see no sign of the oscillations on the power
supply rails to either pre or power amp (the distortion is present at
the pre amp output). Also strange is that sometimes just passing my
hand over the PSU board can cause or cure the fault. Perhaps this
could be a dry joint also?

Any tips on trouble shooting this are welcome.
Best regards,
Greg.


Greg,

I've got a couple of other service notes which I don't think really
apply to your case, but what the heck, have a look at them:

Factory service hint: AC line clicks are audible. Grounding problem of
input jacks. "SOLUTION: mount a **FOIL** 0.33uf, 400V cap between the
housing and the ground of the RCA jacks. The best is to loosen the
screws holding the RCA jacks and clamp one leg of the foil capacitor
between the plastic of the RCA lag and the back panel: the other wire
can be soldered to the ground of the RCA jack.

I've got my own notes mentioning that R823 (150K) can go high in value
which will cause the unit not to function. Preamp lights may be out.

I've got another one where I noted that a bad 5V standby supply filter
capacitor (C502 or C505, C502 more likely) can cause the main power
relay to chatter.

I'd also try poking at the main power relay, in case its got bad
contacts and is arcing. Lastly, I don't think the power supply PC board
is grounded to the chassis through its mounting screws, but I'd check
and make sure that they are tight. I'll let you know if I can think of
anything else.

Regards,
Tim Schwartz
Bristol Electronics
  #12   Report Post  
Posted to sci.electronics.repair
external usenet poster
 
Posts: 5
Default NAD317 Strange Oscillating PSU? More thoughts...



Greg,

I've got a couple of other service notes which I don't think really
apply to your case, but what the heck, have a look at them:

Factory service hint: AC line clicks are audible. Grounding problem of
input jacks. "SOLUTION: mount a **FOIL** 0.33uf, 400V cap between the
housing and the ground of the RCA jacks. The best is to loosen the
screws holding the RCA jacks and clamp one leg of the foil capacitor
between the plastic of the RCA lag and the back panel: the other wire
can be soldered to the ground of the RCA jack.

I've got my own notes mentioning that R823 (150K) can go high in value
which will cause the unit not to function. Preamp lights may be out.

I've got another one where I noted that a bad 5V standby supply filter
capacitor (C502 or C505, C502 more likely) can cause the main power
relay to chatter.

I'd also try poking at the main power relay, in case its got bad
contacts and is arcing. Lastly, I don't think the power supply PC board
is grounded to the chassis through its mounting screws, but I'd check
and make sure that they are tight. I'll let you know if I can think of
anything else.

Regards,
Tim Schwartz
Bristol Electronics


Hi Tim, thanks for your continued interest!
The amp doesn't seem to have any power or protection circuit problems
as you have seen. Still seems to be a grounding or capacitor issue, I
hope to have an ESR meter next week to try.
I don't suppose you have the circuit diagram? That would help some!
The amp is a pig to work on as the PSU board is attached by fairly
sort cables to everything & I even had to unsolder the speaker binding
posts to lift the board to look underneath! You are right that the PSU
board is not grounded to the chassis directly. There is a single black
wire from "chassis" on the silk screen that goes to a solder tag under
one mounting screw, I have cleaned & tightened it. Similarly on the
left hand side of the board one of the mounting screws is used to
provide ground to the speaker output. All in all the standard of
wiring & soldering is poor. I have checked & re solderered anything
suspicious but still no luck.

I found a posting in another group that seems to be the same fault:

http://groups.google.co.uk/group/aus... 55e68187a210

I emailed the guy but had no response.

I will persevere as this is really bugging me!

Best regards,
Greg.
Reply
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules

Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Baxi Solo 2 40/PF fan "oscillating" Mike Dodd UK diy 4 October 11th 17 06:44 PM
Oscillating Spindle sanders Phisherman Woodworking 20 March 17th 07 04:32 PM
Oscillating fan problem BE Electronics Repair 9 August 20th 06 04:17 AM
Oscillating spindle sander Chuck Hoffman Woodworking 3 November 16th 04 07:03 PM
Oscillating Sander Pat & Maryann Dwan Woodworking 3 September 3rd 04 09:08 AM


All times are GMT +1. The time now is 12:10 PM.

Powered by vBulletin® Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 DIYbanter.
The comments are property of their posters.
 

About Us

"It's about DIY & home improvement"