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Sansui QRX-5500 Died changing the lamps

goodshelac

goodshelac

Member
Good Evening AK'ers. So I did a rather stupid thing tonight. I had my 5500 apart on the bench for a cleaning and lamp replacement. I'm a novice at this so bear with me. I changed out the fuse lamps and those were all working great. I needed to replace one selector bulb and I forgot to turn off the power when I clipped the old wires off the circuit board and I think it arced. Now the unit powers on but no lights, no sound, nothing. Checked the main fuse and that's still good. Did I fry this thing or are there other fuses that would have tripped for the lighting panel?? Any insight would be much appreciated.

Thank you!!
 
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Looks like there are a bunch of fuses inside.

Check fuse 01 on F-1483. Heck, check them all.

Rob
 
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Robisne is correct, there should be a dedicated fuse just for the supply voltage to the lamps. In most Sansui gear of this vintage, the lamp supply is a straight tap off a secondary on the transformer - no rectification or filtering - as the lamps work fine on an AC supply voltage.
 
Robisme said:
Looks like there are a bunch of fuses inside.

Check fuse 01 on F-1483. Heck, check them all.

Rob
Click to expand...

Yep. fuse 01 on F-1483 is open, I can see it. There's also a blown fuse on 1482. Now, the issue is fuse 01 on 1483 is wired to the circuit board. I cant seem to get to the solder points to replace this. Any tricks you know of ? Thanks!!
 
I have that backwards. Fuse 01 on 1482 is the wired fuse. There are 8 fuses on 1483 that are all easy to change. Need to get to the underside of 1482.
 
The soldered in fuse is what was referred to as a pigtail fuse. Used to be you could buy a clip on fuse holder to use a conventional glass replacment fuse paralleled with the blown fuse, but I've not seen one of those sold in years now as it was one of those ooddball Radio Shack type items.

Anyway, the wire leads were usually soldered to the endcaps of the fuse, so it is possible you could unsolder the fuse from the leads and solder a new fuse to them from the component side of the board. The correct repair would be to remove the old fuse and leads and install a fuse holder so it will be easier to replace in the future, but the circuit board may need minor modification to do that.
 
Sansuiman said:
The soldered in fuse is what was referred to as a pigtail fuse. Used to be you could buy a clip on fuse holder to use a conventional glass replacment fuse paralleled with the blown fuse, but I've not seen one of those sold in years now as it was one of those ooddball Radio Shack type items.

Anyway, the wire leads were usually soldered to the endcaps of the fuse, so it is possible you could unsolder the fuse from the leads and solder a new fuse to them from the component side of the board. The correct repair would be to remove the old fuse and leads and install a fuse holder so it will be easier to replace in the future, but the circuit board may need minor modification to do that.
Click to expand...
Thank you!! It makes sense but I think it may be above my skill set. I think I should take this in to my tech and see what it'll cost. Thanks for your help. I'll update you with a diagnosis soon!
 
A wise man knows his limitations. Shouldn't be a problem for your technician to do a repair on that quickly.
 
Ok, so my tech was extremely busy and can't get to this for a while. I think I'm going to dig a little deeper myself and try and figure this out. Good news is when I hit the main contacts on the light board with a 9 volt battery, everything lights up. I checked all of the fuses with a volt meter and they are all fine. The F01 fuse on F-1482 which is designated for accessory lights is fine, unless I'm getting a false reading on my VM. It's under a plastic coating so I can't confirm visually unless I cut that piece off. What I'm trying to figure out is what circuit board controls the power supply to that lighting bar? There are 2 wires on either end of the bar which again, when I hit the contacts with a 9volt, they light up. If I can trace those wires back to a board, I can look a little deeper at caps and transistors. Any ideas? The schematic I found on HiFi engine is not easy to read (at least for me):dunno: Thanks! I think I've attached a pic of the light board in question. You can see on the far left the black and white wires. Those seem to supply the power. But where does that power come from? Directly underneath?
 

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The function selection lights (FM, AM, PHONO, AUX) are run through one section of the mode select switch. On a rotary switch this is typically one side of one wafer. I'm not sure about the 5500, but most Sansui receivers turn off the dial scale and tuning meter lamps when not in AM or FM mode, so the power for those lamps also goes through the mode select switch.

The VU meter lamps may be switched off for the rear channels when a two channel mode is selected. Again, I've no specific working knowledge of the 5500 as I don't own one and haven't had one across my bench, so this may or may not apply. In any case, all the lamps except the FM STEREO indicator (which is controlled and powered by the FM tuner) have a common single supply voltage that is almost always unrectified and unregulated AC at about 7 volts and comes right off the transformer as it's own secondary. For UL and CSA listed models at least, a seperate fuse was required to be fitted for the lamp supply. For other markets worldwide, that wasn't always required by local regulation but was still frequently present from my observations.

So, I'm still inclined to say you have a bad fuse. Are all the lamps out (dial scale, meters, function indicators) or just a subset of those? If the former then the common lamp supply is the issue in some manner and the most likely single point of failure is the fuse. If the latter, it's more likely to be a bad selector switch or wiring between boards or other intermediate points in the circuit. Given the circumstances under whuch the lamps failed however, a blown fuse is the logical culprit.
 
Sansuiman said:
The function selection lights (FM, AM, PHONO, AUX) are run through one section of the mode select switch. On a rotary switch this is typically one side of one wafer. I'm not sure about the 5500, but most Sansui receivers turn off the dial scale and tuning meter lamps when not in AM or FM mode, so the power for those lamps also goes through the mode select switch.

The VU meter lamps may be switched off for the rear channels when a two channel mode is selected. Again, I've no specific working knowledge of the 5500 as I don't own one and haven't had one across my bench, so this may or may not apply. In any case, all the lamps except the FM STEREO indicator (which is controlled and powered by the FM tuner) have a common single supply voltage that is almost always unrectified and unregulated AC at about 7 volts and comes right off the transformer as it's own secondary. For UL and CSA listed models at least, a seperate fuse was required to be fitted for the lamp supply. For other markets worldwide, that wasn't always required by local regulation but was still frequently present from my observations.

So, I'm still inclined to say you have a bad fuse. Are all the lamps out (dial scale, meters, function indicators) or just a subset of those? If the former then the common lamp supply is the issue in some manner and the most likely single point of failure is the fuse. If the latter, it's more likely to be a bad selector switch or wiring between boards or other intermediate points in the circuit. Given the circumstances under whuch the lamps failed however, a blown fuse is the logical culprit.
Click to expand...

Thank you Sansuiman! This is really helpful. To answer your question, yes, ALL of the lights are out regardless of the selector knob. SO... I decided to cut the PVC plastic off of that fuse to get a visual reading. (F01) and wouldn't you know it was OPEN! Clear as day. It's a simple 5a fuse. I clipped it off and left the pigtails in place. Now I'm going to try and solder a new fuse b back on to those pig tails and see if that gets those lights going. I'll post again once I have that done. Thanks!!
 
OK as a temporary fix, but you may damage the new fuse with the soldering activity - new pig-tailed fuses are available.

Right. So I'll get those ordered. Thank you for the link!! I need to completely remove that board to install the new fuses, might as well change them all while I'm there? Should probably change all the caps too??
 
Thanks all for your input. I got the fuse back in place and all the lights are working great! Now...on to this Marantz 2010 recap! Stay safe everyone.
 

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