Sansui 7070 to work on... need advice

Steady Eddie

New Member
Hey guys, new member.

As I stated in my intro, I have some tech chops, I've maintained and built guitar tube amps.
I've got a 7070 receiver I'd really like to put some love into. Other than the obvious, which is the electrolytic capacitors, what should I change on this?

I'm sure, due to the popularity of this receiver, that someone has done this job before. Anyone have any parts lists? I have already downloaded and printed out the service manual.


And if not, at least tell me what parts I should be changing besides the electros, any particular resistors, diodes, transistors, etc?
I COULD replace every component on every board, but that would be expensive and probably unnecessary.
Any help or suggestions would be deeply appreciated.
Ed

I'd like to put some really nice components into this and make it something special.
 
I usually replace the coupling caps, and test the other DC caps and primary filters to see if they need changing. Deoxit on the switches, and faderlube on the pots. You also shouild look at the fusable resistors on the driver board. There are probably 10 or 12, and they can drift way up in value and should be changed.
 
Also, I’ve heard of people increasing the size of the main power supply capacitors, I imagine it gives extra reserve power for bass notes?
 
Also, I’ve heard of people increasing the size of the main power supply capacitors, I imagine it gives extra reserve power for bass notes?
Yes, better filtering, but it's not safe to, say, double the capacitance most times, nor is it actually helpful.
Be sure to replace the relay as mentioned in that thread - Omron MY2-02-24DC
 
Yes, better filtering, but it's not safe to, say, double the capacitance most times, nor is it actually helpful.
Be sure to replace the relay as mentioned in that thread - Omron MY2-02-24DC
Thanks, I know from amps with tube rectifiers that too much power supply filtering can cause inrush currents that destroy the rectifier, I didn't know that solid state rectifiers were also susceptible, but with aging receivers maybe not a good idea to push it.

I actually read some of that thread on the 7070 a few days ago, I'm trying to digest what I can. It seems that the obvious things besides electrolytics is the fusible resistors, to replace those with metal film types. I got a mouser cart with those in it already. Then there's the thing with the varistors, replace with two diodes in series, they specify 1n4148, I have a few uf4148, the "ultra fast" type, would they work here as well?

Currently, the receiver is working, though it has intermittent loud "popping" noises. Not sure if it's bad solder joints or maybe something in the signal path, failing electros, etc...
 
Thanks, I know from amps with tube rectifiers that too much power supply filtering can cause inrush currents that destroy the rectifier, I didn't know that solid state rectifiers were also susceptible, but with aging receivers maybe not a good idea to push it.

I actually read some of that thread on the 7070 a few days ago, I'm trying to digest what I can. It seems that the obvious things besides electrolytics is the fusible resistors, to replace those with metal film types. I got a mouser cart with those in it already. Then there's the thing with the varistors, replace with two diodes in series, they specify 1n4148, I have a few uf4148, the "ultra fast" type, would they work here as well?

Currently, the receiver is working, though it has intermittent loud "popping" noises. Not sure if it's bad solder joints or maybe something in the signal path, failing electros, etc...
Just still with the 1N4148, it saves money and here it doesn't need to be super fast.
 
Another question, I'm poring over the service manual. It appears the parts lists that accompany the layout of the circuit boards, like say, the F-2624 driver circuit board, is incomplete, it doesn't list every component on that board. I was hoping I could use it to put together a Mouser order.
Edit: I see there's supposed to be a common parts list for resistors and capacitors only. I'll search that out....
 
So I opened her up, pulled a few boards... the driver board, the power supply board, and the fm muting board. not too worried about the fm muting board, but I figure I'll start with the driver board, I found a parts list for the F2624 for a 9090, I'm guessing the driver board is the same on both units.

Funny thing, on the power supply board, zener diode ZD02 appears to have spewed something on the cathode side of the lead. Of course I'll replace it, but I wonder if that is the reason I was getting loud popping noises on transients. Or could it be symptomatic of another problem?
 
So I opened her up, pulled a few boards... the driver board, the power supply board, and the fm muting board. not too worried about the fm muting board, but I figure I'll start with the driver board, I found a parts list for the F2624 for a 9090, I'm guessing the driver board is the same on both units.

Funny thing, on the power supply board, zener diode ZD02 appears to have spewed something on the cathode side of the lead. Of course I'll replace it, but I wonder if that is the reason I was getting loud popping noises on transients. Or could it be symptomatic of another problem?
The 9090db or 8080DB driver board is the same as the 7070, but not the Sansui 9090 that uses a different driver board. Just check the resistor values as some may be different from the 9090db and 7070
 
The 9090db or 8080DB driver board is the same as the 7070, but not the Sansui 9090 that uses a different driver board. Just check the resistor values as some may be different from the 9090db and 7070
I'll do a check, but I would think a F2624 board would be a F2624 board, no matter what, right?
 
Not all the time. Sansui uses the same board number at times, especially in the G series receivers. Not sure if they did the same with the 7070 vs the 8080db or the 9090db, but would just doublecheck by the list you have and what resistors are on the board you have.
 
I'll do a check, but I would think a F2624 board would be a F2624 board, no matter what, right?

As Tom B says,especially in regards to the fusible resistors.. Some of the components on the F2624 will be different depending on the unit it is used in, and the year, or specific production run as some "in production" changes were made and not documented. Always replace what is on the board and not necessarily what is in the schematic. Be very careful of the BIAS diodes (or the round "can" transistors) mounted on the driver transistor heat sinks. Those thin leads break very easily so don't move them but only a very few times, and not very far at all if you have to. Though not impossible to find, they are extremely scarce. However, you can interchange a complete F2624 board if you have to. But they are almost always rebuild-able unless physically broken. A word of advice, take lots and lots of pictures before you start! Some of the silk screening on these are wrong! 2 diodes near the bottom, and sometimes +/- of some capacitors are backwards.
 
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