FM - Front End Troubleshooting Tips?

[CaseyWKC]

They never drift, they either work or go phut. If no change they're all OK.

View attachment 3825999

Marked in red. It is extremely important to verify the four voltages in order to properly troubleshoot the IF strip. Make very sure you are presenting a strong FM signal, whether off-air, a cheapo MP3 FM transmitter or SG doesn't matter. All four voltages should be like the last one.

Having said that, 2.3 V across C213 is inconsistent with your symptoms (no tuning indicator deflection, low audio). Is H501 OK? DC-wise? C508?

Sorry, meant to get back here sooner.

So all I can find with that board layout that matches my IF board is C213 - on my board this is labeled C208. All of the other components in red are not there on my board. I will attach a picture of my IF board.

C208 reads .600mv on one side and 8.6v on the other.


H501 measurements
pin 1 - 1.4v
pin 2 - 1.4v
pin 3 - .21mv
pin 4 - 9.6v (touching this pin volume got louder in FM, no stereo)
pin 5 - 9.6v

C508 was replaced early on.

Thanks for your help!

 

[CaseyWKC]

Picture of the IF board - also this model has a champagne faceplate.

 

[dankik]

So all I can find with that board layout that matches my IF board is C213 - on my board this is labeled C208. All of the other components in red are not there on my board. I will attach a picture of my IF board.

Here is your photo of the P200 board and the board layout from the document below. These seem to match.
There are two schematics in this document: SN 1001-330 and 3301-3600.

 

[CaseyWKC]

Here is your photo of the P200 board and the board layout from the document below. These seem to match.
There are two schematics in this document: SN 1001-330 and 3301-3600.

View attachment 3838592
View attachment 3838595

Thank you for this.

H501 seems to be okay. L501 seems to be fine.

I took my probe to the anode of H503 and H504 (germanium diodes) and this is what I see tuned into a strong FM station.

Both voltage drops are the same in circuit, voltages are the same when unit is powered on @ anode and cathode of both, one measures in both directions.

.283v drop one way 2.08v the other.

 

[PE9ZZ]

I wasn't aware of different versions of P200 board which rendered my remarks utterly useless. The screenshot of the scope is also useless. This scope has a screenshot to USB function, use it.

The change in volume on touching IC H501's pin#4 is a clue. You say L501 is OK. How can you be sure? What did you test?

And since there seem to be at least three versions of P200, which serial # do you have?

 

[CaseyWKC]

I wasn't aware of different versions of P200 board which rendered my remarks utterly useless. The screenshot of the scope is also useless. This scope has a screenshot to USB function, use it.

The change in volume on touching IC H501's pin#4 is a clue. You say L501 is OK. How can you be sure? What did you test?

And since there seem to be at least three versions of P200, which serial # do you have?

I will make use of that going forward.

I guess realistically I could only confirm that in L501 the adjustment for the centering of the tuning meter has effect when adjusted and I get continuity for the minimum distortion adjustment.

I also had another L501 on hand from a previous marantz and swapped that one in - no change.

S/n on this guy is 2123.

Thank you!

 

[PE9ZZ]

I'd like to see the voltage on H501 pin#4. Should be something like this:


And please, please, pretty please use the printscreen function of your scope.

 

[CaseyWKC]

I'd like to see the voltage on H501 pin#4. Should be something like this:
View attachment 3839149

And please, please, pretty please use the printscreen function of your scope.

Took me entirely too long to set up, NI VISA drivers had me thinking I bricked my computer for a second.

Here's what I see on pin 4 - measures at 9.6v and when I am probing pin 4 now with multimeter I actually lose signal and hear violent popping.

Edit : sometimes it pops sometimes pin 4 makes it much louder and distorted.


Thank you.

 

[PE9ZZ]

Is this correct? 5 mV per div is a thousand times less than what I'm getting. If this is correct the IF chip H501 has gone phut. The DC voltage is due to the transformer so that doesn't say much. Scope pin#1 to see if signal there is OK. Should be about 1 Vpp.

 

[ConradH]

Too late to be useful but the Siglent should be able to save to a flash drive. I've got one at work that's driving me nuts because the VISA driver won't install. Not even sure it will fit. The computer insists it's already installed, which it was years ago, but it isn't anymore. Boo hiss on the giant bloated NI VISA package.

 

[PE9ZZ]

I use a python version of the VISA driver on my Linux machine and that works just fine. The USB drive on the Siglent is an easy option but in my case using it sometimes crashes the scope.

 

[dankik]

@CaseyWKC, your probe setting is not correct. It should be 1X or 10X depending on your switch setting on your scope probe.

 

[CaseyWKC]

@CaseyWKC, your probe setting is not correct. It should be 1X or 10X depending on your switch setting on your scope probe.

View attachment 3840494

Woops good catch, got it set to x10 on scope and probe now.

Is this correct? 5 mV per div is a thousand times less than what I'm getting. If this is correct the IF chip H501 has gone phut. The DC voltage is due to the transformer so that doesn't say much. Scope pin#1 to see if signal there is OK. Should be about 1 Vpp.

pin 1 and pin 4 with probe settings corrected.

 

[PE9ZZ]

I've lost track on the progress on this issue. Original symptom was low volume, no stereo. Volume gets louder when pin#4 of H501 is touched. Its waveform is low-ish but present. Frequency according to scope is nicely close to 10.7 MHz. So I have questions: does scope signal change when lower slug of L501 is adjusted? Does center meter change? Upper slug? I've had internal C's of these IF transformers gone bad, maybe that's the case here too.

Do you have a proper plastic 2mm HEX tool to adjust the cores in L501? If not get it. They are hard to find nowadays. An allen key will destroy the fragile ferrite core(s). And make tuning impossible anyway.

 

[CaseyWKC]

I've lost track on the progress on this issue. Original symptom was low volume, no stereo. Volume gets louder when pin#4 of H501 is touched. Its waveform is low-ish but present. Frequency according to scope is nicely close to 10.7 MHz. So I have questions: does scope signal change when lower slug of L501 is adjusted? Does center meter change? Upper slug? I've had internal C's of these IF transformers gone bad, maybe that's the case here too.

Do you have a proper plastic 2mm HEX tool to adjust the cores in L501? If not get it. They are hard to find nowadays. An allen key will destroy the fragile ferrite core(s). And make tuning impossible anyway.

Correct, volume is still low in FM compared to all other sources.

Volume got louder consistently originally when probing pin 4 of H501 with my meter. Yesterday for whatever reason there were instances where instead of volume improving when probing pin 4 FM made violent popping noises and all reception was lost, only when meter was touching pin 4 of H501.

I can confirm center meter changes when adjusting L501 to center the tuning meter (secondary core).

I will have to take another look at the shop tomorrow to confirm that the primary core is okay, I believe it is.

I also had another L501 around that I swapped to see if there was a change and so I could measure the original out of circuit.

Thanks for taking the time to help, I promise I'm not trying to make anything difficult!

 

[CaseyWKC]

Correct, volume is still low in FM compared to all other sources.

Volume got louder consistently originally when probing pin 4 of H501 with my meter. Yesterday for whatever reason there were instances where instead of volume improving when probing pin 4 FM made violent popping noises and all reception was lost, only when meter was touching pin 4 of H501.

I can confirm center meter changes when adjusting L501 to center the tuning meter (secondary core).

I will have to take another look at the shop tomorrow to confirm that the primary core is okay, I believe it is.

I also had another L501 around that I swapped to see if there was a change and so I could measure the original out of circuit.

Thanks for taking the time to help, I promise I'm not trying to make anything difficult!

Confirmed L501 is functioning, I can center the tuning meter with it no problem and the minimum distortion (pink) adjustment in that transformer works too, I can peak volume with it.

I'm kind of at a loss, thinking about ordering an a replacement for H501 and seeing if that helps any but I'm doubtful.

Having a hard time isolating this to the front end or the detector board.

 

[CaseyWKC]

I've lost track on the progress on this issue. Original symptom was low volume, no stereo. Volume gets louder when pin#4 of H501 is touched. Its waveform is low-ish but present. Frequency according to scope is nicely close to 10.7 MHz. So I have questions: does scope signal change when lower slug of L501 is adjusted? Does center meter change? Upper slug? I've had internal C's of these IF transformers gone bad, maybe that's the case here too.

Do you have a proper plastic 2mm HEX tool to adjust the cores in L501? If not get it. They are hard to find nowadays. An allen key will destroy the fragile ferrite core(s). And make tuning impossible anyway.

last ditch effort here and then I will give up.

Anything I can do short of buying a proper FM signal gen?

Thanks, appreciate all help given.

 

[PE9ZZ]

Anything I can do short of buying a proper FM signal gen?

One of those cheapo car FM transmitters or something from Mr. Ma (aliexpress). I got an Si4713 board but you will then also need a controller for it.