Deciphering an old schematic

[TalismanRich]

I've got some old filter capacitors to replace in a Sony receiver. Looking at the diagram, it's got a strange symbol for the filter cap. I've found two different diagrams for the polarity! Anyone know for sure which side is positive on these two capacitors, bracket or dash? I haven't pulled the caps yet (they are 4 legs, two are blank.) There's no negative indicator on the sides, maybe on the bottom.

 

[Gtoboy]

The trace appears to show the bracket sides joined together which would tend to indicate that is the ground side and you can double check that by locating the ground side of the power supply since it should be on the same trace.

 

[TalismanRich]

I would have thought that, but there is a second 3300uF cap that is connected in the opposite direction according to the trace. I did find a couple of references to this symbol, apparently it's an old style that was common in Japan. Makes sense since it's an old Sony receiver from about '74 or '75.

Looking at the circuit diagram, this all makes sense now since it's on the -25V side of the diode bridge. I guess I missed that notation when I was scanning things.


That's what happens when you're fooling with stuff when you should be going to bed. The ol' brain gets a bit foggy!

It's been AGES since I've seen a power supply with 4 actual diodes instead of a rectifier bridge!

 

[Gtoboy]

I would have thought that, but there is a second 3300uF cap that is connected in the opposite direction according to the trace. I did find a couple of references to this symbol, apparently it's an old style that was common in Japan. Makes sense since it's an old Sony receiver from about '74 or '75.

Looking at the circuit diagram, this all makes sense now since it's on the -25V side of the diode bridge. I guess I missed that notation when I was scanning things.

View attachment 117402
That's what happens when you're fooling with stuff when you should be going to bed. The ol' brain gets a bit foggy!

It's been AGES since I've seen a power supply with 4 actual diodes instead of a rectifier bridge!

Yeah, when in doubt, check the power supply.

 

[TalismanRich]

I love it when a plan comes together. Today I had the time to rip into the old Sony receiver. I pulled the 2 old 3300uF and one 1000uF caps and replaced them with the new ones that came in last Friday. It was really quite an easy job., Construction is typical 1970s Sony, single sided boards, and the parts are labeled on the blank side. It's solidly built for a unit that cost about $150-160. 15W/channel continuous power.


After I replaced the caps, I fired it up. Plugged in a pair of headphones and was greeted with some FM static. The pots were pretty noisy, so I removed the bottom and shot them with some cleaner. That quieted down the pots (the balance control is still a touch scratchy). Even without an antenna, it pulled in 4 FM stations with a decent strength.

I still have my old Marantz 5G speakers, and the Sony turntable. It might be time to check out the crossover in the speakers, and find a nice low cost cartridge (maybe a Grado or AudioTechnica is in order). Real vintage vinyl! 😉

 

[Pinky]

You lost me with the vinyl [I'll "never forget" all its shortcomings or feel nostalgic for it] but great work on bringing back the dead. Older equipment is superior in both right to repair and parts simplicity. They tend to sound just as good as anything made today.

 

[rob aylestone]

I just realised I actually had one of these, bought from the place I worked when I first got a real job. I don't remember what happened to it!

 

[TalismanRich]

This was purchased when my first wife and I were still in college. She had an HST230A, a Garrard 40 turntable and 8 inch Utah speakers that were stolen from her dorm room, along with a bunch of albums. We replace that stereo with the 6036, a pair of Marantz 5Gs and another Garrard, all bought from Rabsons mail order in New York.

Several years after she died, I sold the speakers and turntable, along with my old integrated TA1055 amp to a friend, and kept the 6036, my pair of 5Gs and my Sony 5520 turntable. They worked for years with my 27" Sony TV (with STEREO!) and VCR for a decent sounding video setup, back in the day when most TVs were mono and had at best, a 4x6" speaker. Eventually, it started getting noisy, and I bought a 5.1 Onkyo setup to replace it. It went up in a closet where it sat for probably 20 years.

Putting it back to working state was a bit of a sentimental deal for me. We bought it when we were dating in the early 70s, and I've kept it all this time.

Now, the question is... how in the crap can I remember all these model numbers when I can remember what I had for dinner last night!!!!!!

 

[Pinky]

Now, the question is... how in the crap can I remember all these model numbers when I can remember what I had for dinner last night!!!!!!

Dinner is base. Music can elevate even the worse of days.

 

[dogooder]

What do you use for a desoldering tool? Wick, sucker?

 

[TalismanRich]

I have an old rubber ball solder sucker, and for a final cleanup, I have some wick.

 

[ecc83]

I had one of those Sony receivers. I swapped it with my sister for a Toshiba SA 420. Did alright the Toshy is 25W per chan and discrete power amps. Funny how things come about! Just two days ago I took the covers off to check it out, it is as old as the Sony obviously and not been powered up this five years. Worked though and a wet finger showed the PAs worked. Output DC offset is a fairly reasonable 38mV and there is NO trace of hum even with the VC at max. On phono there is a mild hiss at max vol but again, zero hum.

I would bet there is nothing wrong with those Sony caps? Any trace of white powder or bulging?

I am going to use the Toshiba to amp a Rega gram deck for digitizing vinyl but the deck and amp will be in a bedroom.I have a pair of Fidek speakers as local monitors and I have pulled 36V DC out of the amp to power a balanced line driver I built some years ago. NE5532 driving two OEP A2626E '600 Ohm' transformers to feed the signal to my living room that now houses my hi-fi. Behringer mixer (collects TV digital sound and 2 DVD/CD recorders plus MOTU M4 and feeds all to a pair of Tannoy 5As) I wouldn't normally put transformers in an audio feed but 'tis only vinyl!
I have the op amp/transformer PCB working and the receiver gives around 28V DC to the board. Single rail but I have half a TL072 providing the half supply rail. (the other half was a high Z input in the board's original usage)

I shall post some picture and maybe a schematic if anybody is REALLY interested. It is just stock op amp application and all in my head atmo.


Dave

 

[TalismanRich]

I had bulging on two of the caps. One of the 3300uF ones (the large black ones in the first picture) had a distinct bulge to the top, and one 1000uF looked suspect. Since they were easy enough to remove, and all on the same board, I just replaced them all at the same time.

 

[ecc83]

I had bulging on two of the caps. One of the 3300uF ones (the large black ones in the first picture) had a distinct bulge to the top, and one 1000uF looked suspect. Since they were easy enough to remove, and all on the same board, I just replaced them all at the same time.

Fair enough. That's a pint or three I owe ya Rich!

Dave.