Realistic STA-2100 Restoration

[sanjib]

I recently got a Realistic STA-2100. After listening for a few days I realize it needs recap so I decided to do a full restoration of this receiver.
Regarding accessibility to all boards, it is not very difficult but you need some degree of disassembly.
First I did the power supply board. All of the electrolytic capacitors are replaced with Nichicon caps.
Here is the list of semiconductors replaced in this board:

D702/703 - 10E1 - UF4007
D704 - WZ-130 - BZX55C13
D705/D706 - WZ-200 - 1N5250B
TR701 - 2SD571- KSC1008
TR702 - 2SB605 - KSA708
TR703- 2SC1222 - KSC1845
TR704 - 2SA750 - KSA992
TR705 - 2SD325 - KSC2073

After cleaning up:


Restored:

 

[sanjib]

Next, is the tone board.
All of the electrolytic capacitors are replaced. Capacitors of value 4.7uF and below are replaced with Wima film caps.
Here is the list of replaced semiconductors

TR401/402 - 2SC1222/2SA750 - KSC1845/KSA992
TR403-405 - 2SC1222 - KSC1845
TR1001 - 2SC1222 - KSC1845
TR1501-1504 - 2SC536 - KSC1815
D501/502 - VD1221- Two 1N4148 in series
D503-506 - ITT-73N- 1N4148
D507/508 - SR-1K-8 - 1N4007
D509 - WZ-130 - BZX55C13

Finished board:

 

[sanjib]

Now is the head amp board.
This board is hiding under a metal shield and it also has the selector switch on it.
All of the high-value electrolytic capacitors are replaced and low-value caps are replaced with film capacitors.
Here is the list of semiconductors replaced here:

TR301/302/304 - 2SC1222 - KSC1845
TR303 - 2SA750 - KSA992

Finished board:

 

[Binkman]

Have you done any testing between rebuilding boards?

 

[sanjib]

Have you done any testing between rebuilding boards?

Yes, after doing each board I tested it and it is so far so good!

 

[sanjib]

Protector circuit board. It is very easy to access. All of the electrolytic caps are replaced, the relay is replaced with Omron MY4-02-24DC and trimmer resistors for watt meters are replaced with 1Kohm 0.5 watt bourns.
Here is the list of semiconductors replaced on this board?

TR601/604/605 - 2SC536 - KSC1815
TR602/603/ - 2SD571 - KSC1008
TR606 - 2SA750 - KSA992
D601/602 - 10E1- UF4007
D603 - VD1221 - 2x1N4148

Finished board:

 

[sanjib]

Interesting problem!!!
For 1Khz test tone, both sides have equal output but for the 100-500Hz test tone, the left channel has half of the output of the right channel. After a can of deoxit in all pots and push switches now it is okay and I hope it will stay like that!

 

[sanjib]

Meanwhile, the tuner board is recapped. All of the electrolytic caps are replaced with new electrolytic caps and WIMA film caps.

Cleaned board and finished board

 

[sanjib]

Main amp board. All of the electrolytic caps and resistors of 1watt and higher are replaced. DC offset and biasing trimmer are replaced with bourns.

Here is the list of semiconductors replaced on this board

Diodes:
D501/502 - VD1221 - 2X1N4148 in series
D503-506 - ITT-73N - 1N4148
D507/508 - SR-1K-8 - 1N4007
D509 - WZ-130 - BZX55C13

Transistors:
TR501/502 - 2SA872 - KSA992
TR503/504 - 2SD668 - KSC2690AYS
TR505 - 2SB649 - KSA1220
TR507 - 2SD669 - MJE15032G
TR508 - 2SB649 - MJE15033G


All original outputs are there and still debating myself whether I should replace them or not!

Original:

Cleaned:

Finished

 

[sanjib]

This unit is plagued with dirty switches! Cleaning, cleaning, cleaning....

 

[lowercasee]

Wow, very nice job so far! I have an STA2100D that I brought back to life with the help of the members here. Would love to do a full restore on it but for now, it works and looks great so I'm going to leave it as is. Killer receiver!

 

[sanjib]

Wow, very nice job so far! I have an STA2100D that I brought back to life with the help of the members here. Would love to do a full restore on it but for now, it works and looks great so I'm going to leave it as is. Killer receiver!

I have fully finished the restoration and it is sounding amazing. But one switch is giving me so much pain! It is the bass turnover push switch. After spraying deoxit and working 30 times everything running normal but if I switch off the amp for an hour and then switch it on, the right channel having pulsating DC and then if I work on the switch few times everything coming to normal! A weird problem I never had with any other amp. I may have to change the switch at the end.

I think 2100D is the same amp just without the gigantic toroidal transformer.

 

[lowercasee]

I have fully finished the restoration and it is sounding amazing. But one switch is giving me so much pain! It is the bass turnover push switch. After spraying deoxit and working 30 times everything running normal but if I switch off the amp for an hour and then switch it on, the right channel having pulsating DC and then if I work on the switch few times everything coming to normal! A weird problem I never had with any other amp. I may have to change the switch at the end.

I think 2100D is the same amp just without the gigantic toroidal transformer.

Yeah, I think that is the main difference between the 2 receivers. Sucks about the turnover switch too, I would probably just swap it out too.

 

[sanjib]

Filter capacitors are replaced with United Chemicon 18000uF/75V

 

[llwhtt]

In your opening post you said you realized it needed a full recap, how did you realize that? Were any of the old capacitors bad? Just wondering.

Craig

 

[Skywatcher]

In your opening post you said you realized it needed a full recap, how did you realize that? Were any of the old capacitors bad? Just wondering.

Craig

Age... Electrolytic capacitors slowly become capsistors with age, some worse than others, and some not so slowly putting strain on other components. The goal is reliability more than it is for sonics. Although sonic improvements very often accompany replacing them. Especially signal path caps where film can be used.
Just recently I had an ONLY 20 yr old Yamaha come in that was in protection. The culprit was a Nichicon cap that went dead short. The owner said it happened all of a sudden and had zero problems previously. When something is 40+ years old, the caps are ticking time bombs.

 

[llwhtt]

The OP said after listening for a few days he realized it needed a full recap, I was wondering how he realized that. I've been repairing electronics since 1975 and yes capacitors do have their problems but it not as bad as everybody thinks on these DIY forums. I guess capacitors are easy to replace without ANY electronics knowledge but to have a fully functional receiver and to say "I realized it needed a full recap" just made me wonder how he realized that. And then to see all of the Fine Golds? in the power supply made me think there are better capacitors for that purpose. Were any measurements taken before or after the recap? How about the ESR of the old capacitors? Many times I find the old capacitors measure better than the ones replacing them.

Craig

 

[RadioNerd]

The OP said after listening for a few days he realized it needed a full recap, I was wondering how he realized that. I've been repairing electronics since 1975 and yes capacitors do have their problems but it not as bad as everybody thinks on these DIY forums. I guess capacitors are easy to replace without ANY electronics knowledge but to have a fully functional receiver and to say "I realized it needed a full recap" just made me wonder how he realized that. And then to see all of the Fine Golds? in the power supply made me think there are better capacitors for that purpose. Were any measurements taken before or after the recap? How about the ESR of the old capacitors? Many times I find the old capacitors measure better than the ones replacing them.

Craig

I'm sure this question could be debated in many different directions, because there are so many variables - some technical, and some purely perceptual on the part of the listener. I've also been repairing electronics of all sorts since the 70s. Not everyone has the skill, the time, the schematic, or the test equipment to debug something down to the individual capacitor level. Generally speaking, if your soldering skills are good then it probably isn't going to hurt to do a full recap on 40+ year old audio gear, even if only a handful out of 60 caps are actually bad enough to hear easily. True, you're wasting a certain amount of time and money, but it can be an OK tradeoff because you're probably fixing a few subtle problems you didn't yet know existed, and you'll get to the finish line faster. Sometimes the peace of mind and that "new" feeling make it worth it, rather than having lingering doubts that there may be marginal caps messing up your audio.

 

[HWKI]

Main amp board. All of the electrolytic caps and resistors of 1watt and higher are replaced. DC offset and biasing trimmer are replaced with bourns.

Here is the list of semiconductors replaced on this board

Diodes:
D501/502 - VD1221 - 2X1N4148 in series
D503-506 - ITT-73N - 1N4148
D507/508 - SR-1K-8 - 1N4007
D509 - WZ-130 - BZX55C13

Transistors:
TR501/502 - 2SA872 - KSA992
TR503/504 - 2SD668 - KSC2690AYS
TR505 - 2SB649 - KSA1220
TR507 - 2SD669 - MJE15032G
TR508 - 2SB649 - MJE15033G


All original outputs are there and still debating myself whether I should replace them or not!

Original:
View attachment 1926535
Cleaned:

View attachment 1926536
Finished
View attachment 1926542
View attachment 1926547

I guess we should not be amazed at how similar this main amp board x2 is like the Concept 11.0 receiver. Since both were manufactured by
Radio Shack/Tandy corp. Very nice rebuild. You wouldn't happen to have a parts list from mouser or digikey available?

job well done!

 

[dicko195]

Main amp board. All of the electrolytic caps and resistors of 1watt and higher are replaced. DC offset and biasing trimmer are replaced with bourns.

Here is the list of semiconductors replaced on this board

Diodes:
D501/502 - VD1221 - 2X1N4148 in series
D503-506 - ITT-73N - 1N4148
D507/508 - SR-1K-8 - 1N4007
D509 - WZ-130 - BZX55C13

Transistors:
TR501/502 - 2SA872 - KSA992
TR503/504 - 2SD668 - KSC2690AYS
TR505 - 2SB649 - KSA1220
TR507 - 2SD669 - MJE15032G
TR508 - 2SB649 - MJE15033G


All original outputs are there and still debating myself whether I should replace them or not!

Original:
View attachment 1926535
Cleaned:
View attachment 1926536
Finished
View attachment 1926542
View attachment 1926547

Just pulled the Left Amp board out of my 2100. Bought it new in 1979. Still plays decent. Doing a recap and found several resistors over tolerances. Interesting they didn't put a heat sink on TR505. Great info here. Good work.