[Ron Ramirez]

I bought this receiver a few (or was it several?) months back. I'll post a picture of the outside later. If you want to see what one looks like for now, you can Google the term "Realistic STA-225".

This one is working, but the electrolytics are old and someone replaced two of the audio output transistors at some point, so the sound is less than ideal.

I am going to replace all four audio output transistors, along with the two large power supply electrolytics and all of the other electrolytics in the power supply circuit. I will then see how it sounds and go from there.

Here's a look at the areas I will be concentrating on.

[Image: http://www.philcoradio.com/images/phorum/STA225_001.jpg]

These two electrolytics to the left of the power transformer will be replaced.

[Image: http://www.philcoradio.com/images/phorum/STA225_002.jpg]

Under all of those wires is the power supply board, which is held onto the main chassis with two screws. It may be a bit of a challenge to get to these caps.

And, guess what...no schematic! So this will just be a matter of replacing specific parts. I hope.

[Ron Ramirez]

Let's start with...the death caps.

[Image: http://www.philcoradio.com/images/phorum/STA225_003.jpg]

If you look closely at the one on the right, you will see that the case is cracked. So it needs to be replaced.

[Image: http://www.philcoradio.com/images/phorum/STA225_004.jpg]

I have freed one end of each of the old line-to-ground caps. I've also discovered that the mystery component hidden under the plastic sleeve is a 2.2 megohm resistor.

I replaced all three components and...

[Image: http://www.philcoradio.com/images/phorum/STA225_005.jpg]

New X1/Y2 safety caps and a new 2.2 megohm resistor, hidden inside black heatshrink tubing.

Since I have done this, I have also removed the original power supply electrolytics and physically replaced them with new 8200 uF Nichicons (they are not yet wired into place underneath). The new caps are the same diameter as the old ones, but the new ones are about 1/3 as tall as the originals.

more to come tomorrow...

[gregb]

I look forward to you getting this one fixed up, I bought this receiver brand new back in the 70's. It was my very first brand new unit and it sure did see a lot of service. The only problem I had with it was the on/off switch failed a couple times over my years of ownership.

Gregb

[Ron Ramirez]

I could only dream of owning a set like this back in 1975...I was 15 years old in '75 when this set was new. I recall seeing them in Radio Shack's 1975 catalog and thinking $400 was a figure I could never afford...this was their top of the line model back then...

...well, now I finally have one. It just took a few years to save up the money. Okay, a few decades.

[gregb]

So I must have bought an old stock model as I bought the set in 1977 with speakers and turntable. My sister inlaw still has the speakers and I still have the turntable. The receiver is long gone.

Gregb

[Ron Ramirez]

For the 1977 model year, the STA-225 was replaced by the STA-235, an all silver-faced receiver with 55 watts per channel, a slight improvement over the STA-225's 50 watts per channel.

So your STA-225 was a leftover from the previous year, obviously never sold until you bought what may have been your local Radio Shack store's last unit of that model.

The STA-2000 made its first appearance in the '77 catalog. It was the first Radio Shack "monster" receiver, 75 watts per channel. I have the later version STA-2000D which made its first appearance in the '79 catalog.

I know all of this only because I looked through the Radio Shack catalog archive:

http://www.radioshackcatalogs.com/

Great reading material for when you have the time to browse.

If you go to the '76 catalog and look on page 21, you will see that Radio Shack offered three different "Everything Systems" (receiver, speakers, turntable) that year featuring the STA-225. RS may have put together different packages in Canada, though.

[gregb]

I do recall the STA-2000 and would have loved to have got it but as it was what I bought was around $900 at the time and that was a small fortune for me. I paid half that for my first car. My Dad thought I was out of my mind.

Gregb

[Ron Ramirez]

Greg, that is really neat that you owned one of these STA-225s when it was new!

In 1977, I was about to graduate high school...would start working in radio the following year at a nickel above minimum wage which was...what? Around $2.15 an hour or so in '78. On that salary no kid could afford a $400 receiver. I made do with a cheap Sears (or was it J.C. Penney?) all in one table unit which had AM-FM stereo, turntable, and 8-track all in one unit that my parents gave me a year or two before then.

It came with some equally cheap speakers. As a high school project I built a pair of 2-way speakers using woofers and tweeters from McGee Radio in Kansas City. These were much better even though the drivers were also cheap. I must have kept the all-in-one until I bought that Sherwood S-8900A in the early 1980s in a junk store for $5, not working. I kept the DIY speakers until I bought a pair of BIC Venturi towers at a yard sale some years later. Then I thought I really had a great setup...and I guess I did for a second hand system. By then (early 1990s) I had traded a radio for a Technics SL-D3 turntable, and together with a cassette deck bought new, I was set for awhile. The Sherwood died sometime in the early-mid 90s and was replaced by a new Pioneer purchased at Worst Buy. By then most receivers had become BPC, nothing to really be proud of like the older receivers were.

I said all that to say this...I was just thinking that the only pair of speakers I ever bought new were a set of Auvios from Radio Shack four or five years ago, upon the recommendation of Peter Balaszy (who is on the other forum). They are small but are 3-way units that sound very good. Of course now that I have discovered Bozak, no other speaker will do for me. I have the E-300s in my home office and a set of Urbans in the living room.

Okay, enough rambling for now.

[gregb]

I just flipped through the catalog and it was the STA-225 receiver, the T100 tower speakers and I don't see the turntable in the catalog so I wonder if it was something different in Canada. I will go have a look at it and see what model number is on it. I still use it and with a little maintenance it still works good.
We are lucky here, good paying jobs have been plentiful for many years. Anyone not working here just plain doesn't want to work.

Gregb

[gregb]

I just checked the turntable and it is an RD-8100 which I can't find in any of the catalogs. I did some online searching and it was offered in the Canadian market only and was available in the mid to late 70's and was made by a company called CEC and they made some Hitachi and Marantz tables, it is similar to the LAB-420 . That's all I could find.

Gregb

[Ron Ramirez]

Today's progress so far: I have replaced all of the electrolytics in the power supply section of the receiver.

[Image: http://www.philcoradio.com/images/phorum/STA225_006.jpg]

[Image: http://www.philcoradio.com/images/phorum/STA225_007.jpg]

Notice how short those new Nichicon main filters are! Fortunately they are the same diameter as the originals, so they had no trouble fitting into the original can clamps.

Next up: To replace the output transistors.

[Ron Ramirez]

Time to replace the output transistors!

[Image: http://www.philcoradio.com/images/phorum/STA225_008.jpg]

New transistors and new mica insulators.

I decided to try applying the heat sink compound to both sides of each insulator with a Q-tip. It resulted in a much neater job:

[Image: http://www.philcoradio.com/images/phorum/STA225_009.jpg]

and now all four transistors are in place:

[Image: http://www.philcoradio.com/images/phorum/STA225_010.jpg]

Notice that there is very little excess heat sink compound, which was my goal.

Notice also that one of the transistors is missing a mounting nut. The receiver was like this when I bought it. Of course the nut is metric...and after spending over an hour looking through a large tin I have filled with various bits of hardware, I discovered that...of course, I don't have one.

I don't want to do a halfway job and solder the pins of this transistor to the PC board until I have a nut and lockwasher in place, and have the transistor secured to the heat sink.

So...unless I can rob one from another receiver I happen to have here, this job will be on hold until next week. I have a currently non-working STA-2000D, and I'm going to open it up and look at it later. I looked inside another Japan-made receiver, a Fisher 202 Futura parts set, but it did not have one.

[Ron Ramirez]

As it turns out, the answer to my metric nut dilemma was found in one of the clamps holding a large electrolytic capacitor in place.

I removed the screw and nut which tightens the clamp, replaced screw and nut with a 4-40 screw and nut, and used the metric nut from the clamp for the last transistor. Perfect fit. The lockwasher came from my hardware tin.

[Image: http://www.philcoradio.com/images/phorum/STA225_011.jpg]

The electrolytic and clamp are back in place with the new screw and nut:

[Image: http://www.philcoradio.com/images/phorum/STA225_012.jpg]

And a quick frontal shot of the receiver:

[Image: http://www.philcoradio.com/images/phorum/STA225_013.jpg]

The sound is very smooth...through headphones at least.

But there is another problem.

The dial pointer is supposed to turn red when an FM Stereo station is tuned in. It does not. No voltage is getting to that bulb. Which means that FM is only in mono.

...and now I really need that schematic...the service info I have does not include a schematic...

[Ron Ramirez]

After much searching online, I found a schematic. I also found a thread on AudioKarma which points to the potentiometer that sets the 19 kc signal getting dirty and causing the decoder circuit to fail.

So...before bedtime, I'm off to hit that trimpot with DeoxIT.

[Ron Ramirez]

Okay!

We have FM Stereo reception! I checked with my FM Stereo transmitter and a song which has obviously separate information in left and right channels. Yes, it is definitely receiving in FM Stereo. However...the dial pointer does not turn red. Neither dial pointer lamp is coming on.

I checked...the FM Stereo pointer lamp, PL9 I think, seems to be OK (around 7 ohms) but the other lamp, PL8, is open; which explains why the pointer is never illuminated.

Here's a partial schematic - click to enlarge:

[Image: http://www.philcoradio.com/images/phorum..._014sm.jpg]

I'm wondering if transistor TR307 has gone bad? It appears to control the PL9 pointer lamp. The only other components in this circuit are two resistors, R332 and R333. Or maybe the circuit will not work without a good PL8?

Let's all enjoy our Christmas dinners, and afterwards, I'll look forward to your thoughts. Merry Christmas.