Sansui QRX-9001 2x power mode problem

[Kane4040]

Hello all,

I am working on a QRX-9001 with an issue in 2x power mode. The unit has been fully refurbished with appropriate replacement parts similar to:

Sansui QRX-9001 fix, restoration et. al

I was having trouble with the F2624 driver boards so I went ahead and purchased two of the following from affinity for artifacts:

https://www.ebay.com/itm/127806676037

I am unable to find any errors with the new boards thus far. Voltages check out.

Here is the symptoms. The unit works fine in all modes except 2x.

When engaging 2x mode with the bias set above 15 ma the unit starts drawing excessive current and goes into protection. With lower bias the unit does the same if a signal is applied.

I noticed when testing that the signals coming off of tr5 and tr6 on f2636 are not inverted, but am unsure if this is normal.

All suggestions are appreciated.

 

[sansui 74]

I purchased a QRX 9001 from QRX restore in Eugene Oregon 2011 and Jim the owner sent me an email explaining that they found other units with a component in backwards from the factory can’t remember if it was a cap or diode on the 2X power board he also explained if in th 2X power mode if it sounded distorted this was most likely the cause.
Jim has since passed but his sons continued the company you can contact them here tech@qrxrestore.com Justin his son will know about this issue.
Maybe this will help good luck. Ken

Hi Ken,
Well, this is indeed interesting about the 2X power stereo mode. I
only just figured this out last week. As far as I can tell every single
9001 shipped from the factory had this cap in backwards. It is marked
that way in the printing on the component side of the board. Before
last week, we replaced these caps in the same polarity that they came
from the factory. This means that yours is in backwards, and detracts
greatly from the usability of the 2X mode. I doubt that the cap would
explode, as I have not seen a single instance of it in all the units we
have worked on. And yes, that cap got replaced as part of the complete
recap we do. It could be taken out and reversed, although I would
recommend using a new cap if that was going to be done. If you want to
do it, or if you have some one there local who could do it for you, I'll
send you a cap. It's a 12 cent item, as we buy them, but probably
pretty difficult to acquire if you're not buying in multiples of 100.

If you happen to be passing through Eugene, I'd be glad to do it for
you, no charge. Takes about 1/2 hour.

It's funny to be doing this for years, and then figure something like
this out. I thought I had this receiver wired. 9001's have always
popped to some degree when being switched to this mode, but I never
worried about it. With that cap put in right, it's noiseless, and the
sound in 2X mode is very nice sounding stereo.

Thanks,
Jim


On 04.03.2012 14:55, kenwsf@aol.com wrote:
> Hi Jim
> I read your post on the 2 channel option for the 9001, sounds
> interesting which I have not used yet, if I understand right the cap
> in question needs to be in the right polarity, did this cap get
> replaced in the overhaul? of the set I have if so I just need to turn
> it around or should I just replace to be safe caps don't like to be
> reversed bias and can explode. Thanks for your help Ken

 

[Kane4040]

I purchased a QRX 9001 from QRX restore in Eugene Oregon 2011 and Jim the owner sent me an email explaining that they found other units with a component in backwards from the factory can’t remember if it was a cap or diode on the 2X power board he also explained if in th 2X power mode if it sounded distorted this was most likely the cause.
Jim has since passed but his sons continued the company you can contact them here tech@qrxrestore.com Justin his son will know about this issue.
Maybe this will help good luck. Ken

Hi Ken,
Well, this is indeed interesting about the 2X power stereo mode. I
only just figured this out last week. As far as I can tell every single
9001 shipped from the factory had this cap in backwards. It is marked
that way in the printing on the component side of the board. Before
last week, we replaced these caps in the same polarity that they came
from the factory. This means that yours is in backwards, and detracts
greatly from the usability of the 2X mode. I doubt that the cap would
explode, as I have not seen a single instance of it in all the units we
have worked on. And yes, that cap got replaced as part of the complete
recap we do. It could be taken out and reversed, although I would
recommend using a new cap if that was going to be done. If you want to
do it, or if you have some one there local who could do it for you, I'll
send you a cap. It's a 12 cent item, as we buy them, but probably
pretty difficult to acquire if you're not buying in multiples of 100.

If you happen to be passing through Eugene, I'd be glad to do it for
you, no charge. Takes about 1/2 hour.

It's funny to be doing this for years, and then figure something like
this out. I thought I had this receiver wired. 9001's have always
popped to some degree when being switched to this mode, but I never
worried about it. With that cap put in right, it's noiseless, and the
sound in 2X mode is very nice sounding stereo.

Thanks,
Jim


On 04.03.2012 14:55, kenwsf@aol.com wrote:
> Hi Jim
> I read your post on the 2 channel option for the 9001, sounds
> interesting which I have not used yet, if I understand right the cap
> in question needs to be in the right polarity, did this cap get
> replaced in the overhaul? of the set I have if so I just need to turn
> it around or should I just replace to be safe caps don't like to be
> reversed bias and can explode. Thanks for your help Ken

Thank you very much for your reply. I had seen that post qxrestore and experimented with different caps/orientations to no avail. The problem manifests when I run it at slightly above average levels in 2x power mode. I have ordered some new ceramic caps for the driver boards that I will install upon arrival Tuesday in case there is an oscillation problem associate with the caps I have installed now.

I will keep this post updated. Also attaching a picture of one of the boards:

Brian

 

[Kane4040]

Thank you very much for your reply. I had seen that post qxrestore and experimented with different caps/orientations to no avail. The problem manifests when I run it at slightly above average levels in 2x power mode. I have ordered some new ceramic caps for the driver boards that I will install upon arrival Tuesday in case there is an oscillation problem associate with the caps I have installed now.

I will keep this post updated. Also attaching a picture of one of the boards:

Brian

Update. Ceramic caps changed to modern equivalents. No change.

Bias and power draw rise when placed in 2x mode eventually resulting in a triggering of the protection relay.

Picture with the new ceramic caps installed: