Realistic STA-2100D Restore - no AM Reception

TechGuru87

New Member
Hi, I am nearing the end of a Realistic STA-2100D restore, I have rebuilt both amp boards, protect, relay, power supply boards, replaced large filter caps and done many other repairs as needed with all new LED's. It looks & sounds great the FM Stereo works great but absolutely no AM reception at all. I am not sure what the problem is? I have followed other members troubleshooting methods. Checked voltages at IC203 (HA1197) they seem ok based on posts here but the schematic I got from HiFi Engine gives no voltages for the tuner section. Instead I used the 2100 (non-D) service manual as a reference. I injected an 1khz signal into pin 12 of HA1197 and get audio output. I also tried the IR Remote test and no pulses in AM. I have thoroughly cleaned the Tuner section but still no AM. All I get is static and popping across the whole AM Dial. Could it be IC203? How can I be sure it needs to be replaced. Anyone have any other troubleshooting ideas? Thanks in advance...

Here are the voltage readings for HA1197 - in AM Mode
Pins (1) 5.09v, (2) 2.2v, (3) 10.15v, (4) 7.23v, (5) 10.15v, (6) 3.65v, (7) 1.3v, (8) 2.5v, (9) 7.5v, (10) GND, (11) 11.10v, (12) 0v, (13) 1.4v, (14) 0v, (15) 0v, (16) .9v

TR203 (C945) Voltages - in AM Mode
(E) .86v, (C) 6.88v, (B) 1.47v

I forgot to mention that there is no signal meter movement in AM mode
Also, I ordered a few HA1197's from eBay today...
 
Last edited:
Hi, Should I move this post to the Tuner's forum since it's a problem with AM Reception? If so, how do I move it? Thanks...

Moved to the proper forum by a mod, thanks...
 
Last edited:
If you recapped the tuner board. Double check your work. Lifted / cracked pads or runs. Polarity and sizing of the caps. That HA1197 is doing most of the work here. Without a signal generator and oscope, best bet after checking your work is to replace the chip.
 
Hi All, here's an update. replacing HA1197 made no change. I did find a more complete service manual with actual voltages for the 2100D. Based on my original voltage readings in previous post I am missing 1.5v on Pins 12 & 14 of IC203 (HA1197). Where does the 1.5v come from? is it an internal voltage or an external voltage that is missing? I do have an signal generator and digital oscilloscope. I can inject AM modulated signals into the AM RF circuit at Pin 1 of the IF Board but cannot tune in any AM Stations just static noise. One other concern I have is I found that wires were soldered in reverse coming off the Front End Board to the IF Board from another shop. Based on the 2100D schematic the wire from pin 11 on Front End Board should be connected to Pin 1 on IF Board & the wire from pin 12 on Front End Board should be connected to Pin 2 on the IF Board. They were reversed I have since corrected them but didn't discover this until after I replaced IC203 (HA1197). With those wires being reversed could that damage the new IC? Also, can someone confirm this is the correct wiring order because I found a discrepancy in the service manual on page 22 trimmer locations diagram as to the position of AM2 (AM RF) & AM3 (AM OSC) trimmers on the tuner assembly and page 38 Front End PCB (Top & Bottom views) says AM2 trimmer is connected to pin 12 & AM3 trimmer is connected to Pin 11. Are these mistakes in the service manual? Hope this isn't to confusing because I had difficulty how to explain it in writing. Any help would be greatly appreciated. Thanks...
 
Hi All, Another update. It's been over a month now and after taking a break from the 2100D it's back on the bench where I left off. I finished recapping the rest of the boards (Phono EQ Preamp, Tone Amp board and Tuner board). I replaced the HA1197 IC again, on my third one since the other new one must have been damaged by reversed wires as discovered in my previous post. I can now partially align the AM and can tune in a local station but very weak and can't pull in distant stations. The static and popping is still present across the entire AM dial this is not off air noise nor can I hear off air noise. I even replaced TR203 (AM output amp). Another thing I noticed is when first switching to AM there is no AM reception or any noise present at first then after a few seconds the noise ramps up like a cap is charging. Since I recapped all the boards except Ceramic, Mylar and polystyrene, What could be causing this noise in the AM? Does anyone know where I should start tracing the signal path to locate the abnormal noise? The FM side works perfect. If I figure out how to post an audio clip of the noise I will. Thanks in advance...
 
If you recapped the tuner board. Double check your work. Lifted / cracked pads or runs. Polarity and sizing of the caps. That HA1197 is doing most of the work here. Without a signal generator and oscope, best bet after checking your work is to replace the chip.
Hi Mike, I posted a couple updates since your last reply. Can you please take a look at them and let me know your thoughts and how to proceed with my AM Tuner Problem. I have made some progress but can't track down the constant static and popping noise in the AM side. Thanks for your help...
 
AM is very susceptible to noise. Most modern devices create noise. You may be hearing local interference. May need some tweaking on the alignment.
 
TG87 - I'm not intending to step on any toes here, since pX is the obvious Sultan of Signal, Tzar or Tuners, and Monarch of Megahertz, but I might be able to throw in a few general suggestions.

Can you see a 455KHz (or thereabout) IF difference after the mixer, perhaps at Pin 1 of the IF board? That's somewhat critical. Does the AM3 section trimmer cap have any effect?

As for noise, if you have about five minutes, it might be informative to review this thread - pX alluded to this problem earlier: http://audiokarma.org/forums/index.php?threads/service-bench-shielding.855627/
The noise on my bench was kicking me in a sensitive spot whenever I tried any AM work, and even on some FM. I basically had to shut nearly everything off to quell the interference and be able to dial in anything. All the non-zero crossing, switch-mode crap out there today is killing AM, not to mention some of the band infringement by other commercial RF sources.

Just speculating here, but the slow rise of signal in the AM section could be a cap. If you monitor voltage on Pin 3 of the HA1197 or positive end of C264, does that coincide with the signal rise?

Regarding the schematic, I can't help there since I don't have a unit for reference, but only the same schematic.
 
I set the 2100D aside for the moment as I have an SX980 going on the bench shortly which coincidently uses the HA1197 IC, maybe I can use that as a reference? As for the 2100D interference was my first thought so I eliminated almost all sources of external interference in the beginning , my shop is in a basement type shelter and I barely get cell phone reception unless by a window. None of my other receivers are picking this AM noise up so I have reason to believe it is internal. I still have to fully align the AM so hopefully the problem goes away?

Some other shop really messed up the AM, it took me weeks of troubleshooting and repairs just to dial in the 455KHz signal. I am going by the schematic as there seems to be a discrepancy in figure 29 on page 22 under AM IF & RF Alignment as where AM2 & AM3 trimmers are located. I will use everyone's suggestions and hope to make some progress. Stay tuned for another update. Thanks for getting back...
 
Hi Everyone, Here's another update. Still no progress and I'm ready to throw in the towel. When I was able to dial in the 455KHz signal it was with the board removed from the chassis for easy access. I had to unsoldered pins 1 & 2, 36 & 37 on the IF Board and used jumpers and connect as per the schematic for testing purposes. Once I got it dialed in it would receive a local channel but still the constant static and popping (sounds like a bad transistor) but where? I recapped the entire receiver and replaced only TR203 (AM output amp). The FM works perfect so I don't want to replace any transistors on the FM side. What other transistors did I miss? Another strange thing is I can only dial in the 455KHz signal and receive a station as long as the gray wire from Bar Antenna is not connected to pin 37 on the IF Board Also I put the IF board back in place and mounted back to the chassis with original screws and left pin 37 disconnected I get the same symptom. So if the IF board is grounded to chassis or at pin 37 I loose all AM signal except the constant static and popping. Is there anyone out there that has a 2100D that they can take and post pictures of how Pins 1 & 2 are supposed to be connected to the tuner board and what color wire goes to Pins 36 & 37 on the IF board from Bar Antenna? The 2100 & 2100D schematics do not match and 2100D service manual has discrepancies so I do not know the correct wiring. I don't want to blow another HA1197 since this is my third one which appears to work as long as the IF Board is not reconnected to the chassis and Pin 37 is left disconnected. Thanks for everyone's help...
 
TG87 - I'm not intending to step on any toes here, since pX is the obvious Sultan of Signal, Tzar or Tuners, and Monarch of Megahertz, but I might be able to throw in a few general suggestions.

Can you see a 455KHz (or thereabout) IF difference after the mixer, perhaps at Pin 1 of the IF board? That's somewhat critical. Does the AM3 section trimmer cap have any effect?

As for noise, if you have about five minutes, it might be informative to review this thread - pX alluded to this problem earlier: http://audiokarma.org/forums/index.php?threads/service-bench-shielding.855627/
The noise on my bench was kicking me in a sensitive spot whenever I tried any AM work, and even on some FM. I basically had to shut nearly everything off to quell the interference and be able to dial in anything. All the non-zero crossing, switch-mode crap out there today is killing AM, not to mention some of the band infringement by other commercial RF sources.

Just speculating here, but the slow rise of signal in the AM section could be a cap. If you monitor voltage on Pin 3 of the HA1197 or positive end of C264, does that coincide with the signal rise?

Regarding the schematic, I can't help there since I don't have a unit for reference, but only the same schematic.

Hi Watthour, Once I dial in the 455KHz signal everything looks good and the AM3 trimmer does change the signal. After I dialed in the 455Khz signal and continued the alignment I was able to pickup a local stations and all voltages look good including at Pin 3 of HA1197 & C264 but the constant static and popping is still very much there across the whole AM dial. See my latest update on the continuing saga. Thanks...
 
Last edited:
Back
Top Bottom