Sansui 990DB - no output -no tuner activity

[Sansuiman]

Ok. I believe 1/4 were utilized as appropriate (fusistors removed were replaced with same rating both for resistance and power) so I suppose I'm ok. If I need to go back in there for something I may install fuses then as an added measure of protection. Thanks for the clarification.

 

[Robisme]

Rob, are you stating you simply put fuses in place of the resistors?

That is correct.

Rob

 

[Robisme]

I found the pic of my fuse mod, but I like Skywatcher's fix better.

Hey, it was 2008, what can I say. The issue with my repair is that the fuse holders would have to be removed to pull the tuner section out.
But the fuses are easily replaced, not that they will ever need to be.



Rob

 

[Skywatcher]

I found the pic of my fuse mod, but I like Skywatcher's fix better.

Hey, it was 2008, what can I say. The issue with my repair is that the fuse holders would have to be removed to pull the tuner section out.
But the fuses are easily replaced, not that they will ever need to be.

View attachment 1742588

Rob

I did one like this (my first), then went to a similar setup like yours. But I just used the screws for the transformer pan to mount the holders, and a piece of fish paper for protection. The bracket uses thumb screws to the tuner assembly for quick removal.

 

[Sansuiman]

Rob and Skywatcher, thanks for the added information. I think for now I'll simply leave it as is, don't see much risk of the metal films causing a problem.

Kind of funny to think I've never seen a "blown" fusistor (to the extent I've ever tested those I replaced). The typical failure mode is them just drifting off value. They drift far enough and then you see the magic smoke. Guess I've been lucky in that I've never had a unit damaged by a catastrophic fusistor failure. It pays to be proactive I suppose.

 

[DaSpark]

Hi,

Well all I got from the shop yesterday were normal metal film resistors. I got a few 1/4 watt ones but most of them are 1 Watt do you think that is too dangerous to use?

All the best,
Ferdinand

P.S. Added also a picture of my driver board

 

[DaSpark]

Hi Everybody

Just replaced the 1 Ohm fusable resistors on the main power supply for now. And...

I have SOUND Wohoo.

Tuner works aswell.

Currently measuring DC Offset.

On one channel it jumps back and forth between -30mV and +20mV and anything in between

The other channel measures around 110mV Offset.

I guess I have to recap the entire thing What is your opinion?

Thank you again for your help so far

All the best,
Ferdinand

 

[Sansuiman]

Congratulations, nice to hear it is up and rrunning. Yes, absolutely do the full recap, you have a very nice receiver there and it is worth the effort if ypu intend to keep and uae it.

 

[ivandezande]

Hi Everybody

Just replaced the 1 Ohm fusable resistors on the main power supply for now. And...

I have SOUND Wohoo.

Tuner works aswell.

Currently measuring DC Offset.

On one channel it jumps back and forth between -30mV and +20mV and anything in between

The other channel measures around 110mV Offset.

I guess I have to recap the entire thing What is your opinion?

Thank you again for your help so far

All the best,
Ferdinand

Full recap.
I would replace at least the input transistor pair on the driver board with KSC1845. Replace the trimmers too. Offset and bias will be easier to set.

 

[DaSpark]

Hi,

I managed to adjust the offset on the channel that was off by 100mV to around 15mV.

The offset does not seem to get stable. Even after leaving the receiver on for more than 30min in still jumps around quite a lot. (I must admit i use a digital hand held multimeter that roughly comes from the same time period as the 9090DB ) maybe i should get a new one?! or is this expected behavior?

Does anybody have an recap list I could use? I read there should be one from tnsilverman but i cant seem to find it.

All the best,
Ferdinand

 

[Skywatcher]

Hi,

I managed to adjust the offset on the channel that was off by 100mV to around 15mV.

The offset does not seem to get stable. Even after leaving the receiver on for more than 30min in still jumps around quite a lot. (I must admit i use a digital hand held multimeter that roughly comes from the same time period as the 9090DB ) maybe i should get a new one?! or is this expected behavior?

Does anybody have an recap list I could use? I read there should be one from tnsilverman but i cant seem to find it.

All the best,
Ferdinand

The DC offset always dances around on these. That's why it helps to gain match TR01-04 to tame it down some. That "cap list" (actually a BOM) was made from a 9090DB that was an early production unit and may not be exactly the same as yours. Some changes were made while in production. But it will be at least 98% accurate. It is for the F-2624 with the 2SC984 BIAS transistors (little "cans" on the driver transistors) so if yours uses the STV-3H BIAS diodes (Horseshoe shaped brown color), it will be a little different, but not enough to worry about. Here it is for the 9090DB..

 

[DaSpark]

Thank you Skywatcher

Attached there are a few detail pictures of my F2624 Board.

Shall I replace the TR-01 - TR-04 with the 522-ZTX694B as per the recap list you provided or are the KSC1845 a better match?

All the best,
Ferdinand

 

[Skywatcher]

Thank you Skywatcher

Attached there are a few detail pictures of my F2624 Board.

Shall I replace the TR-01 - TR-04 with the 522-ZTX694B as per the recap list you provided or are the KSC1845 a better match?

All the best,
Ferdinand

View attachment 1745076 View attachment 1745077 View attachment 1745078 View attachment 1745079 View attachment 1745080

The ZTX transistors have a EBC pinout and can be very confusing to use. You must twist the B and C leads so they do not short out. Plus you need to buy quite a few, perhaps 40 or more in any given batch in order to get 4 that match. The KSC1845 are ECB and drop right in and sound just fine. Plus they are very consistent in gain from the same batch so you only need to buy maybe 20 or less to gain match 4 of them closely. BUT get them on tape instead of bulk.