Troubleshooting Realistic STA-52B

[DrewSilich]

Purchased a cheap realistic sta-52b that was described as "will not turn on" .

Unit was missing the main fuse and immediately turned on when inserting a fuse. All lights are functioning and AM FM radio works. Unfortunately my luck ended there. Here are the issues i observed

1) With the switch on AUX. There is a rapid ticking that comes through the speakers regardless of where the volume is at and regardless of having anything plugged into the RCA AUX input jacks
2) no ticking when the switch is on phono until i plug something into the RCA Phono input jacks
3) AM/FM pulls in radio stations but sound quality seems a bit off. It sounds as if the bass gets clipped when turning up the bass/volume.

This is my first time attempting to repair a vintage receiver and am trying to learn. After alot of reading i decided to start with testing the following transistors with a fluke 117. These were all tested in circuit with the power off.It seems as if they are all bad based on the readings i got? I find it hard to believe they are all bad! Any tips or suggestions where to go next or what to try.

 

[avionic]

These were all tested in circuit with the power off.It seems as if they are all bad based on the readings i got?

You can not accurately test transistors in circuit...
Hence all the irrelevant readings..
BTW .. Welcome aboard...

 

[ecluser]

Did you clean the switches and controls with some electronic contact cleaner? In this receiver, the signal from the tuner, phono inputs and auxiliary inputs all go to the pre-amplifier with different components in the feedback loop according to the selected input. The Tape input bypasses the pre-amplifier stage. In my opinion you should work with the Tape input first. Once you will have good sound from the Tape input, it's time to work on the pre-amplifier stage.

 

[DrewSilich]

Did you clean the switches and controls with some electronic contact cleaner? In this receiver, the signal from the tuner, phono inputs and auxiliary inputs all go to the pre-amplifier with different components in the feedback loop according to the selected input. The Tape input bypasses the pre-amplifier stage. In my opinion you should work with the Tape input first. Once you will have good sound from the Tape input, it's time to work on the pre-amplifier stage.

Yes i did deox all of the controls and switches. It cleaned up some scratchyness but did not solve any problems. I'll start looking at the tape input.. currently it will play but has a deep hum.. Also notice the right channel sounds better than the left channel. Thanks. i guess i'll start tracing voltages.

You can not accurately test transistors in circuit...
Hence all the irrelevant readings..
BTW .. Welcome aboard...

Well i wasted alot of time with all of those readings but learned something so Thanks! I guess i will go back and start checking voltages etc in the circuit.

 

[avionic]

TR411 thru 414 need to be pulled and double checked. One or more may actually be shorted.

 

[mbz]

Great that you are using the unit as a learning exercise.
Suggest a health check of the power supply checking DC voltages at pins 8,14, 17, 3 also check for any spikes in voltage corresponding to the periodic clicks you are hearing. Assuming no scope, you could try using your fluke to measure voltages in the audio path again looking for any voltage spikes, start at R401,2 (pins 1&9 on main amp board) then move forward toward outputs or back towards preamp if spikes not/present.

 

[raycarr00]

 

[Ashp123]

Did you clean the switches and controls with some electronic contact cleaner? In this receiver, the signal from the tuner, phono inputs and auxiliary inputs all go to the pre-amplifier with different components in the feedback loop according to the selected input. The Tape input bypasses the pre-amplifier stage. In my opinion you should work with the Tape input first. Once you will have good sound from the Tape input, it's time to work on the pre-amplifier stage.

Hi, new member here and a complete audio novice. Hoping you can help with the following question. I have this amp and wanted to know whether a bluetooth receiver should be connected to the AUX input or the Tape-in input.

 

[mbz]

AUX/TAPE-IN are for audio signal input. If your bluetooth receiver does D/A conversion and keeps the output below 2Vp-p (or abouts) then either could be used, most would use AUX. Are there any grounding issues using BT?

 

[Ashp123]

AUX/TAPE-IN are for audio signal input. If your bluetooth receiver does D/A conversion and keeps the output below 2Vp-p (or abouts) then either could be used, most would use AUX. Are there any grounding issues using BT?

Hi, thanks for replying. Its a fairly budget BT receiver with audio out - https://www.amazon.co.uk/dp/B07YTKQ78N?th=1
The sound from both tape in and AUX sound pretty much the same to me. The comment above "The Tape input bypasses the pre-amplifier stage." got me thinking which input would be best to use

 

[mbz]

The comment above "The Tape input bypasses the pre-amplifier stage." got me thinking which input would be best to use

Yeah, a little unusual so I had to check, "ecluser" is 100% correct, the Tape IN does not go through the first gain stage. Handling of Reel-2-Reels is becoming a dying art. So you do have a choice. Using the Tape in to have minimum components in audio path so should be cleaner.

The sound from both tape in and AUX sound pretty much the same to me.

Yep, have a good listen then decide which if any sounds better.

 

[ecluser]

If the input signal is high, like a CD player (they have 3V peak max output), the first preamplifier stage might be overloaded because it is located before the volume control. The Tape In is the best input for a high level signal source.