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Replacing internal fuse in Technics SA-300 receiver

suburbanbeat

suburbanbeat

New Member
Hi all. Pardon my incredible ignorance here. My understanding of electronics is as basic as it gets.

The lights and FM signal strength meter do not function, and I suspect that it has to do with the internal fuse (not the speaker fuses on the back of the unit). The text next to the fuse says "F1 3A-125V".

A Google search of this yields results that are not straight forward. What kind of fuse am I looking for here? Will it be easy to find online or at my local hardware store? Thanks much!
 
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Hello suburbanbeat. Welcome to AK. looked up the Service Manual on HiFi-Engine.com. https://www.hifiengine.com/manual_library/technics/sa-300.shtml . I think the fuses may be standard 3AG size, 6.35mm (0.25 inches=1/4 inch) wide, 31.75 mm (1.25 inches) long. F2=2Amps 250Vac,F3=1Amp 250Vac,F4=1.6Amps 250Vac. If the fuses are the size I listed you should be able to find them locally (hardware store, lowes and such). The fuses should be located in the left side close to the front of the receiver after you remove the cover. Remember to unplug the receiver from the AC line before opening the unit. The bad fuse should look empty, (no filament wire inside the fuse). If needed take a picture and post here.
 
NAD80 said:
The bad fuse should look empty, (no filament wire inside the fuse). If needed take a picture and post here.
Click to expand...

First of all, thank you for the quick and super detailed response!

BUT, I did remove the fuse and dust it off. Filament still in tact. Fuse is good, apparently. When I removed it the receiver wouldn't power on at all. Point being that it doesn't appear that this is what is responsible for the lights and FM signal strength meter.

I did order some replacement bulbs that are to the exact specifications of the original bulbs (6.3V, 125A). I just hope they fit the sockets. Anyway, that will tell me if it is, in fact, a bulb issue and not something else. But since both the FM signal meter and bulbs are non-functioning, I suspect that there a common issue responsible for both. Does that sound right? What should I look for in this case?
 
F2 powers the lights. Did you check both the other fuses F1,F3? Also do you have a meter?
 
signal strength meter runs from fm circuit so if fm is working the meter has a problem or the selector switch is corroded . does the meter work on am ?
lights run off fuse 2 as stated . lamps are in parallel so its the fuse or all 3 lamps are blown
 
Thanks again for all of the help so far. AM signal meter DOES work, but I get nothing when scanning through FM frequencies.

F1 is in plain sight, right where you said it would be, but I can't find F2 or F3 for the life of me. Am I looking for the same type of fuse as F1? If so, they're elusive. Attaching photos below.
upload_2017-7-9_0-3-3.png
F1 is in the upper left of the photo here.

upload_2017-7-9_0-4-7.png
Looking towards the front left of the receiver (assuming we are looking at the receiver straight on). F1 in the upper center of the photo.

upload_2017-7-9_0-6-5.png
And the front right, as if we were looking at the receiver straight on. No obvious fuses in sight, or am I just Mr. Magoo-ing this one?
 
fuse should be at the end of the brown wire coming from transformer .. brown and blue are for the lights
 
Yes, the fuse by the end of the brown wire is F1, which as far as I can tell is still a good fuse. There are no other fuses like that anywhere inside. Hmmmm... There are two additional fuses on the rear, but those are just for the speakers, right? Either way, those are both good, too.
 
According to the PCB layout right behind the headphone jack. But it does look like just 1 fuse is mounted on the PCB. Since F1 is the only one found. Have to trace the wiring then. Is it a 120Vac unit? The two rear fuses are for the speakers protection. Look for the yellow wire, goes to D702 powers the IC 401,402. The brown and blue wires off the transformer power the lights (6.3Vac, 250ma bulbs).
 
Looking at the photo above C616 looks to have gotten quite warm, (shrunken label on the cap). If that cap is going it could bring down the voltage to the power modules IC 601, IC602.
 
Yeah, so I'm looking at the diagram now, and the fuses are really just not where they are supposed to be. According to PCB layout, F2 and F3 should be directly next to F1 and they... aren't. Nothing there, not even mounts for a fuse. Why would that be?
 
Note that the service manual available on HFE is NOT for the US/Canada version, it's the Europe, Asia, Latin America, etc. versions - (X) (XA) (XAL) (XGH) (E).

Had the same issue with my SA-500, The model designation shows SA-500 (M) for USA and SA-500 (MC) for Canada. It does change the number of internal fuses.
 
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TPettenati said:
Note that the service manual available on HFE is NOT for the US/Canada version, it's the Europe, Asia, Latin America, etc. versions - (X) (XA) (XAL) (XGH) (E).

Had the same issue with my SA-500, The model designation shows SA-500 (M) for USA and SA-500 (MC) for Canada. It does change the number of internal fuses.
Click to expand...

Shoot, well that would certainly explain the discrepancy. Thank you for pointing that out. I would have gone a little mad wondering why I had a freak unit.

I'm expecting new bulbs any day. Hopefully they fit and work. Either way, there would still be the lingering issue of the non-functioning FM signal strength meter. I'll post when I've tested the new bulbs.

Thanks again for all of your help.
 
suburbanbeat said:
Yes, the fuse by the end of the brown wire is F1, which as far as I can tell is still a good fuse. There are no other fuses like that anywhere inside. Hmmmm... There are two additional fuses on the rear, but those are just for the speakers, right? Either way, those are both good, too.
Click to expand...


"As far as I can tell"...did you try replacing it?
Have you used a meter to check for continuity?
I've seen fuses that "look good" but that were indeed blown.
 
So, I finally got replacement bulbs, and as I mentioned in my other thread regarding the replacement of those bulbs, they work great. So the lamp issue is resolved.

The only lingering issue is the FM signal meter. Again, AM meter works fine.
 
suburbanbeat said:
Thanks again for all of the help so far. AM signal meter DOES work, but I get nothing when scanning through FM frequencies.

F1 is in plain sight, right where you said it would be, but I can't find F2 or F3 for the life of me. Am I looking for the same type of fuse as F1? If so, they're elusive. Attaching photos below.
View attachment 964112
F1 is in the upper left of the photo here.

View attachment 964113
Looking towards the front left of the receiver (assuming we are looking at the receiver straight on). F1 in the upper center of the photo.

View attachment 964114
And the front right, as if we were looking at the receiver straight on. No obvious fuses in sight, or am I just Mr. Magoo-ing this one?
Click to expand...
my SA-300 only has one internal fuse...my SA-400 has 3
 
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