Marantz 2215 FM Decoder troubleshooting...

[btmacdou]

I am just finishing up a restore of a 2215b I got a while back. New lamps, cleaned up pots and switches. Chassis looks good and everything works EXCEPT the FM stereo.

I put a new lamp in but when that did not work I tested the old one and sure engouh, it was still good. This means that either the Hitachi HA1156 decoder chip is bad, or the alignment is off and it is just not switching to stereo.

The FM section sounds very good and clean (in Mono!). The front end pulls stations in fine, but it never switches to stereo.

I traced the lamp back through the stereo/mono selector switch and thats all fine. If I ground the control line at the decoder chip, the stereo lamp lights up just fine.

What technique can I use to determine if this is just an alignment problem or if the decoder chip is indeed bad?

I have a scope at hand and am not afraid to use it! Oh and I do not yet have a service manual...

 

[catrafter]

The 2215B service manual is here. If H302 is on due to insufficient IF signal strength (or shorted C-E), the HA1156 (H301) will be forced to mono. H303 should be on for AM, but if it's shorted (C-E) that will kill the VCO. Which 'control line' are you grounding?

Tom

 

[btmacdou]

Thanks Tom. I'll check out the manuals. The pin I was grounding is the output pin to the stereo lamp. The output is apparently an open collector that sinks the pin to ground when it turns on. This provides a path to ground for the lamp, which turns it on. I have not had a chance to look so I'm not sure exactly which pin it is, but the wire from the lamp lands on a wire-wrap pin next to the HA156. It looks lime there Is a resistor in series with it, probably serves as a current limiter.

In the next few days I'll have time to look closer.

I'm hoping it's not the chip since I'd lime to test out a couple of alignment tools I have but not used...

Bruce

 

[catrafter]

If you have a counter, try the the VCO alignment at step 5 on page 3 of the service manual or you could tune in a strong known stereo station and rock R302 to see if the stereo lamp pops on.

Tom

 

[btmacdou]

So now I'm in the market for a frequency counter. Checking eBay, there are many many for sale, including some brand new 2.4ghz counters selling for less than $130.

Any suggestions on where to start? How much should I spend? Should I trust an older uncalibrated unit if it comes from HP or other popular brand?

(PS: I have sent a suggestion to AK to start a forum dedicated to test gear and general restoration tips)

Bruce

 

[btmacdou]

Maranzt 2215b FM stereo troubleshooting

Tom,

I bought a Frequency counter and used it to check the 19khz pilot signal on the HA1156. I tweaked R302 to get it to 19.001 khz. After about an hour of warming both the receiver and the counter up, the signal drifted a bit between 18.9x and 19.2x. How stable should this signal actually be?

Also, I tested the two transistors you mention. H303 seems to be turning on and off just fine, but H302 does indeed appear to be shorted CE. I tested it with my dvm with the reciever turned off and measured less than 200 ohms between C-E. Is this a sufficient test?

Assuming that this transistor is indeed shorted, my question is why? This is a small signal transistor and it's not connected to any large loads. It should last nearly forever! What would cause it to short?

So, that's where I'm at. I did purchase a couple of HA1156 chips but have not installed them pending the results of this more throurough testing.

It will be at least another week before I can do any more testing (gotta go on a business trip) but I look forward to your comments!

Bruce

 

[PB_Audio]

(PS: I have sent a suggestion to AK to start a forum dedicated to test gear and general restoration tips)

Bruce

Sounds like a good idea to me. ...or, maybe a sticky. +1 :yes:

 

[catrafter]

The 19kHz pilot should be very stable when you are TUNED to a stereo station so that the VCO has a pilot to lock on to. Off station it will drift.
Subbing in a new transistor is a quick way to identify the problem. Stuff fails from time to time.

Tom

 

[btmacdou]

Marantz 2215b FM Stereo Decoder Troubleshooting

I have made great progress, but there is still a puzzle. Here is the next chapter:

1. I thought H303 was shorted C-E but it turns out that it works fine. I pulled it an made a simple tester on a breadboard to have it turn on a small LED. So I reinstalled it.
2. Next, I decided to replace the HA1156 decoder chip with a brand new one. This did not solve the problem. The FM was still stubbornly stuck in Mono, no stereo light.
3. So I studied the datasheet for the decoder chip and saw that grounding pin 8 forced the chip into mono. This is what Q302 does. It appeard that Q302 was conducting all the time, so to test the theory that it was bad, I simply pulled it which released pin 8. Voila! Instant stereo, complete with the lamp! Why did I not notice this before? I suspect that I got H303 and H302 mixed up in early testing, probably because my work schedule forced me to spread out the troubleshooting.
4. Now the curious part: The Mono positon on the front panel selector still seems to work just fine without H302 ... Why?? It appears that I could simply leave H302 out of the board and everything will work fine. What am I missing?

I also noticed that once the decoder chip switched into stereo, the 19khz pilot locked right in to 19.001khz. While in mono, it wandered by .5khz or so. What explains this behaviour?

Depending on the answers I get to this, I may or may not replace Q302. It would be easy and cheap to replace though.

I bought two new HA1156 chips for a total of about $10. I installed one of them and am certain that the original that was removed is still good, so I still have two spares.

It's been a fun ride and I've learned several things. Next up is to restore my Sencore mutiplex generator and try out front end tuning on an old Scott tube tuner.

Bruce

 

[JBL GUY]

Congratulations on your success.

 

[btmacdou]

All this for one of the low end Marantz receivers... Ah Well, I may swap it out for the Kenwood KR2120 that I bought new in '72 that has served as my alarm clock since I bought it. It has survived 3-4 on-off "sleep" cycles every day for more than 35 years. How's that for reliability!

 

[catrafter]

If H302 is on due to insufficient IF signal strength (or shorted C-E), the HA1156 (H301) will be forced to mono.

Tom

What is the DC voltage on the base of H302 when you are tuned to a strong stereo station?

Without tracing out the spaghetti that is the schematic, I suspect selecting FM MONO simply sums the left and right audio and breaks the path to the stereo lamp. It would be easier to just follow the wires than to trace it out on the schematic.

Tom

 

[btmacdou]

Marantz 2215b Stero/Mono troubleshooting

I traced the schematic again and H302 is controlled by signal level in the FM front end. This explains why the selector still works, and also explains the true function of H302: It switches the receiver to FM when the signal qualify falls below a pre-set level. Once the signal reaches this level (as when one is driving closer to a city) H302 will switch the HA1156 back into stereo mode. So, as long as one listens only to strong FM stations, It will stay in full stereo mode.

That said, it appears that there is a possibility of mis-alignment in this signal path since the source of the switching base voltage of H302 is just upstream of variable resistor R161. See attached schematic capture.

I'll do a little more testing of the suspect transistor, and measure the open circuit base voltage to make a final determination of the issue.

Bruce

 

[catrafter]

The pot, (R161) should only affect the level at which the receiver unmutes when the FM Muting button is depressed.

Tom

 

[btmacdou]

Well... I replaced transistor H302 and the problem persists. The base of the PNP transistor never gets above .5 volts. Does a PNP turn on with positive Vbe? I forget...

At this point the decoder works if I simply leave H302 out of the circuit. I may just leave it that way for good...

Bruce

 

[Joshstereo]

I have the exact same issue with my 2215B, ever solve it? I cant leave H302 out of the board because it makes a bit of a sequel in stereo, although that may not be because of H302. Also my fm muting when pressed completely cuts out the sound, the meter doesnt move when tuning either.

 

[x-rayrad]

I also have the same problem with a 2215B, with H302 out I have stereo. Replaced H302, H303, H110, H111, Diodes H118 and H119 with no luck so far.
This seems to be a common issue with this model which means back to the schematic. The FM muting and meter act exactly the same as you described.
Has to be part failure, I have aligned and realigned the front end, ratio detector, etc.
I will update if I find the issue.

 

[x-rayrad]

I have the exact same issue with my 2215B, ever solve it? I cant leave H302 out of the board because it makes a bit of a sequel in stereo, although that may not be because of H302. Also my fm muting when pressed completely cuts out the sound, the meter doesnt move when tuning either.

Did you ever find out the issue with your 2215B?

 

[Joshstereo]

No not yet, ill be trying a fm alignment soon and see what happens

 

[catrafter]

The adjustment of L107 is critical for stereo operation.
If the incoming station, the tuner front end or the IF gain is weak then the circuit mostly composed of H109/L103/H118/H119 won't be able to turn H302 off to enable the multiplex decoder, H301 to decode stereo (If H301 pin 8 is at or near zero volts, then the decoder is forced to mono operation).
In the last 2215B I rebuilt, L107 was bad and I had to get one by buying a donor board from the auction site.
To adjust L107, tune in a strong stereo station and monitor J114 with a voltmeter. Use the proper alignment tool to adjust L107 for maximum positive voltage, which should turn H302 off.

Tom