Hi,

Anybody have any experience in diagnosing the P300 circuit?

I have a 2230 which will receive an FM broadcast, but will not output stereo audio, and the STEREO lamp does not come on (the STEREO lamp is good). Signal strength appears to be good. I've checked the muting control voltages from P550 to verify that the muting signals to P300 are not present (indicating adequate IF signal level and no excessive HF noise present in detected audio).

Checked DC voltages on H301 - 303; all indicate the transistors are biased properly (for no muting). Looked at the 19KHz pilot signal at the collector of H302, and it reads 1.7Vp-p -- doesn't that seem low?

I noticed I could make this signal much bigger (and make the STEREO light come on momentarily) by tapping on L301 or L302, so I suspected I had a cold solder joint. I removed P300 (what a pain), replaced C301 & C302 while I had the board out, reheated all of the solder joints to the left of L302 (in the schematic), and fired it back up. Now the voltage at the collector of H302 is around 0.9 Vp-p. Still no stereo. Sigh.

I'm starting to think I've got a bad L301 or L302? Tapping no longer helps.

Can anyone tell me what the normal peak to peak voltages of the 19KHz pilot signal should be at the collector of H301, H302, and what the peak to peak amplitude of the 38KHz signal at the base of H304 is in normal operation (I wish I had another receiver to look at, but I don't)?

Any other ideas?

Thanks,

Bob

Bob,
First, welcome to AK, please stop by the introduction area and tell us a bit about yourself.

I had the opportunity to view those waveforms recently and fortunately noted their amplitudes. All reading were with a strong (85 dBf) stereo signal using a 100 MHz scope and a 10:1 probe to prevent loading.

H301 collector : 2.2 VP-P
H302 collector : 4.5 VP-P
H304 base : 2 VP-P
H304 collector : 10.4 VP-P
BTW, I've never seen those transformers fail.
I hope this helps!

Tom

Tom,

Thanks for the quick response!

After I got your reply, I also found some (poorly organized and imcomplete) notes I had taken several years ago while working on a 2245 with a similar problem. (At the time I had a working 2230 for comparison). I also took a reading off of C304, and was surprised at how low it was (~20mVp-p) compared to the collector of H301 (200mV). So I thought maybe C304 was partially open and I replaced it with no improvement. While I had C304 out, I checked L301 for continuity to the takeoff point from both ends of the coil, and it was OK. So I don't think it's the coil either.

Since H301 and H302 seem to be amplifying their respective base signals OK, I'm wondering whether I have sufficient signal into this board from the FM Detector (via the muting amp board P550, of course). Unfortunately my old notes didn't show the amplitude of the input signal at J301, but I did note the signal levels at the output of FM Limiter Amp H501 (pin 4), and on the ends of the ratio detector diodes:

H501 pin 4: 500mV
H503+: 800mV
H503-: 200 mV
H504+: 200 mV
H504-: 550mV

On this receiver, the H501 output is 450mV (OK), but the voltages on the diodes are only reading around 20-40mV. I guess this is a long way of asking if you know what the p-p voltage input is on J301 (mine's around 20mV)?

Thanks in advance!

Bobster,
With a strong (85dBf) signal, no audio modulation, only pilot and subcarrier, this is what I read on my 2230.
I wonder if when you noted your readings you forgot to factor in a 10:1 scope probe.
H501 pin 4: 4V p-p
H503 (anode) 3.5V p-p
H503 (cathode) 1.4V p-p
H504 (anode) 1.53V p-p
H504 (cathode) 4.5V p-p
J301 200 mV p-p.
What do you have on J501? Mine is 1.25V p-p.

Tom

Try adjusting the coil on the stereo detector board (not sure of number)--small 2" X 3" board to the left of the AM and FM Multiplex boards.
Sometimes adjusting the coil helps.

I have seen that problem when the MPX IC (SIP type) is bad. It is located under the shielded cover near the back of the receiver. Unfortunately, the IC is no longer available. I'm out of state right now so have not access to my notes.
The 2245 uses a different IC for that function.

DH

I have seen that problem when the MPX IC (SIP type) is bad. It is located under the shielded cover near the back of the receiver. Unfortunately, the IC is no longer available. I'm out of state right now so have not access to my notes.
The 2245 uses a different IC for that function.

DH

Consolidated has TA7060 (http://www.ceitron.com/semi/semi.phtml?part=ta7060) ICs.

Tom

Tom,

Thanks again for the readings. (And I confirmed my readings are corrected for the 10:1 scope probe.)

After organizing my readings and comparing them against yours (I'm using an off the air station as my signal source, so I can't control the signal strength), I'm starting to think I've got a problem on the FM Detector board rather than the FM MPX Decoder.

IF in on J501 reads 1.0, which is fairly close to your 1.25...IF to detector coil from H501 pin 4 reads 2.0V, while yours reads 4.0V -- lower but I'm guessing still enough to detect?...but looking at the signals on the detector diodes H503 & H504, mine are down an order of magnitude from yours, and so are the audio outputs to and on the FM MPX Decoder board P300.

I took DC readings across C508, and I only have 0.33V being developed across this capacitor. I believe its supposed to be 2 diode drops less than the peak to peak voltage on the secondary of L501, which I would think is more than 0.33V (do you have this reading?). Maybe C508's leaky?

So I'm going to take P500 out, check H503 & H504, replace C508 (I'll probably replace all the electrolytics on this board while I've got it out), and see what that does.

It may be a day or two before I can get this done and post back what I find, but I *will* post back...any other suggestions?

Thanks again for your help!

Have you tried Morgan's suggestion of turning the coil some ? Just be sure to mark where you started from . Tune into a strong channel , your SM should have the coils ID in the alignment section . This has worked for me in the past , sorry have never touched a 2230 but on my 2240 and 2250 this helped .



Barney

Oerets,

Yes, I tried this (a little), but it didn't seem to have any effect.

Thanks for the suggestion, though.

Bobster,
I get about 4 VDC across C508 under the signal conditions described above.
H503 and 504 check as .3 V forward and infinite (OL) reverse, in circuit, with the diode test on my Fluke meter.
The primary and secondary windings of the discriminator transformer (L501) read a fraction of an Ohm as one would expect.
I have a spare discriminator transformer, it's out of a 2220B, but has the same part number as the one my 2230.
Shoot me a PM with your mailing address if you want it.

Tom

Tom,

Replacing the discriminator transformer fixed the problem!

And after replacing all the electrolytics in the FM sections and the power amps, this thing sounds great!

Many thanks for all your help on this!

Bob

Bobster,
I get about 4 VDC across C508 under the signal conditions described above.
H503 and 504 check as .3 V forward and infinite (OL) reverse, in circuit, with the diode test on my Fluke meter.
The primary and secondary windings of the discriminator transformer (L501) read a fraction of an Ohm as one would expect.
I have a spare discriminator transformer, it's out of a 2220B, but has the same part number as the one my 2230.
Shoot me a PM with your mailing address if you want it.

Tom

I think the stereo indicator is a pair of 6.3v/40ma bi-pins wired in series, hopefully that's what's in there, wrong stereo lamps have been known to eat the IC. :thumbsdn:

Thanks, but there's only one IC in the 2230, the FM IF Limiter/Amp in the discriminator.

The 2230's STEREO lamps are driven by a discrete transistor (H305) on the FM MPX Decoder board P300, and are wired in parallel.

I was going through the same agonies as bobster with a Marantz 2270 - tuning stations okay, but no stereo separation or stereo indicator. The tip off in my case was no deflection of the center tuning meter (a feature absent on the 2230), so I knew the problem was most likely in the detector circuit, around L501. Found a few leaky caps, and therefore replaced all the 'lytics on the P500 board, no luck. Tested H503 & H504, confirmed all proper voltages at H501 and H502. Even went so far as to confirm continuity of all windings on L501. Nothing.

Finally decided to check online to see if anyone else had run into this particular issue, and found this thread. Nah - couldn't be the discriminator transformer....could it?? I happened to have an old detector board from a 2230 in my junk box, and after confirming basic visual similarity between the two transformers, I swapped 'em out. Sure enough - the center tuning meter sprang to life, and after a few minor adjustments to the slugs, the beacon flickered on and she was singing in glorious stereo!

If I hadn't have seen this thread, I'd never have guessed the discriminator transformer would have gone bad. I even compared continuity measurements between the two transformers, and they were identical. Of course, a shorted winding wouldn't make much difference in such a low resistance measurement, but would certainly throw the part out of whack - perhaps that's what happened. Or, some mindless "tech" diddled the cores so far out of alignment that the few turns I tried had zero effect.

Bottom line, AK ROCKS!! :rockon: Many thanks to bobster for this post, and particularly for his follow-up!!! :thmbsp:

I purchased a 2230 yesterday in pretty good condition. A few bulbs out but have figured that out. The aluminum power button cover is missing ... I may turn a new one.
But here is the question:
When the receiver is in FM mode and I am tuned to a station, and the stereo light is ON .... I only get sound through the right side. That of course changes if I push the MONO button in (turns off STERO indicator light) it plays on both sides but in MONO.
The amp works fine in AUX mode with my iPhone and produces good separation (the amps seem to both work)
I suspect a loose wire or a cold solder joint.
Unfortunately I am not very good with schematics. Do you have any thoughts? It sound like the same transformer issue above ... can you buy these somewhere
Thanks
Joseph