I need to identify two elements (their values) on the board (PST417F) from the above mentioned columns. One is a choke marked L502 and a capacitor marked C76. Will someone help?

Photo, buddy, clear photo of this plate (on both sides) ... it will be hard to remember.

Here you are (better my camera can't):

I see two outputs, either find the schematic (which may not be easy) or measure these items in the second column. Do you have access to capacitance and inductance measuring instruments? Expect this capacitor to be something a la 100nF, but it's shooting in the dark. However, it is better to measure.

The measurement from the second column is out of the question. Unless someone has better meters than mine. I need the value of these items preferably from a service shop. This capacitor is not 100nF. Unfortunately.

Have you tried to write a mail asking the manufacturer for a diagram? Crate didn't bother me with that.

Haven't tried - but a good suggestion. I'll try tomorrow.

Unfortunately - the Italians are silent.

Call me, it's better handled over the phone.

Hello, the question as above is only about one tiny element that has been lost to me. What is a coil, resistor or maybe a jumper? Thank you in advance for your help and best regards.

A colleague of neither pear nor parsley in someone else's thread puts in some photos? In addition, in the photo, both elements are in place.

RCF Art 715: Identifying L502 Choke & C76 Capacitor Values on PST417F PCB Board

Świr 16977 27

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How can I identify the values of the L502 choke and C76 capacitor on the PST417F PCB?

L502 is identified as a BLM21PG331SN1D choke, but the thread does not definitively identify C76’s value. The only concrete advice for C76 was to measure it or find the schematic/service documentation, because the 100 nF guess was rejected as incorrect [#21085689] [#16797551] [#16797555] The manufacturer was also contacted, but no diagram or value information came back [#16806642]

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#1 16796521 02 Nov 2017 17:58

Świr Świr

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Post #1
16796521 02 Nov 2017 17:58

I need to identify two elements (their values) on the board (PST417F) from the above mentioned columns. One is a choke marked L502 and a capacitor marked C76.
Will someone help?
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#2 16797077 02 Nov 2017 20:49

yogi009 yogi009

Level 43

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Post #2
16797077 02 Nov 2017 20:49

Photo, buddy, clear photo of this plate (on both sides) ... it will be hard to remember.
#3 16797464 02 Nov 2017 22:36

Świr Świr

Level 34

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Post #3
16797464 02 Nov 2017 22:36

Here you are (better my camera can't):
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#4 16797551 02 Nov 2017 23:21

yogi009 yogi009

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Post #4
16797551 02 Nov 2017 23:21

I see two outputs, either find the schematic (which may not be easy) or measure these items in the second column. Do you have access to capacitance and inductance measuring instruments? Expect this capacitor to be something a la 100nF, but it's shooting in the dark. However, it is better to measure.
#5 16797555 02 Nov 2017 23:24

Świr Świr

Level 34

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Post #5
16797555 02 Nov 2017 23:24

The measurement from the second column is out of the question. Unless someone has better meters than mine. I need the value of these items preferably from a service shop. This capacitor is not 100nF. Unfortunately.
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#6 16797575 02 Nov 2017 23:38

yogi009 yogi009

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Post #6
16797575 02 Nov 2017 23:38

Have you tried to write a mail asking the manufacturer for a diagram? Crate didn't bother me with that.
#7 16797642 03 Nov 2017 02:32

Świr Świr

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Post #7
16797642 03 Nov 2017 02:32

Haven't tried - but a good suggestion. I'll try tomorrow.
#8 16806642 07 Nov 2017 09:26

Świr Świr

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Post #8
16806642 07 Nov 2017 09:26

Unfortunately - the Italians are silent.
#9 16806726 07 Nov 2017 10:16

yogi009 yogi009

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Post #9
16806726 07 Nov 2017 10:16

Call me, it's better handled over the phone.
#10 17003817 31 Jan 2018 21:27

borys.stw borys.stw

Level 9

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Post #10
17003817 31 Jan 2018 21:27

Hello, the question as above is only about one tiny element that has been lost to me. What is a coil, resistor or maybe a jumper?

Thank you in advance for your help and best regards.
#11 17003873 31 Jan 2018 21:45

yogi009 yogi009

Level 43

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Post #11
17003873 31 Jan 2018 21:45

A colleague of neither pear nor parsley in someone else's thread puts in some photos? In addition, in the photo, both elements are in place.
#12 17004088 31 Jan 2018 22:55

borys.stw borys.stw

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Post #12
17004088 31 Jan 2018 22:55

I borrowed a photo to show the item that was lost. There is no need to set up a new topic.
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#13 17004188 31 Jan 2018 23:34

yogi009 yogi009

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Post #13
17004188 31 Jan 2018 23:34

I wonder if the forum rules also see the need.
#14 17004191 31 Jan 2018 23:38

borys.stw borys.stw

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Post #14
17004191 31 Jan 2018 23:38

One simple question, what is this item. The subject speaks of the device in question and the same problem that I have. So why should I set up another topic, how can I refresh it?
#15 17004243 01 Feb 2018 00:18

yogi009 yogi009

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Post #15
17004243 01 Feb 2018 00:18

You mean the C130? The description suggests a capacitor. Give the markings of these mosfets, maybe the application will tell you something (I would always start with 100nF).

Added after 5 [minutes]:

Still slightly edited for better readability.
#16 17004322 01 Feb 2018 01:40

pikarel pikarel

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Post #16
17004322 01 Feb 2018 01:40

The capacitor is marked with a black arrow and there should be no problems with identifying the type of element.
The marking of the element marked with a red arrow and the letters VR can mean a varistor, i.e. a varistor.
https://ec.kemet.com/varistor-mov-voltage-protection
#17 17004759 01 Feb 2018 11:22

yogi009 yogi009

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Post #17
17004759 01 Feb 2018 11:22

pikarel wrote:
The capacitor is marked with a black arrow and there should be no problems with identifying the type of element.

And what capacity do you read from?
#18 17005351 01 Feb 2018 15:21

pikarel pikarel

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Post #18
17005351 01 Feb 2018 15:21

A colleague clearly asked:

Quote:
(...) What is a coil, resistor or maybe a jumper?
Thank you in advance for your help and best regards.

and I answered the question exactly.
Electronics is a science, not poetry.
#19 17005618 01 Feb 2018 17:26

yogi009 yogi009

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Post #19
17005618 01 Feb 2018 17:26

You are literally right, but in practice it adds little to the topic.
#20 17014144 05 Feb 2018 10:49

borys.stw borys.stw

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Post #20
17014144 05 Feb 2018 10:49

Hello, I was able to determine that VR3 is a thermistor, but I do not know what resistance it should have and whether it is an NTC or PTC thermistor.

Please help.
#21 17014676 05 Feb 2018 14:59

pikarel pikarel

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Post #21
17014676 05 Feb 2018 14:59

borys.stw wrote:
Hello, I was able to determine that VR3 is a thermistor, but I do not know what resistance it should have and whether it is an NTC or PTC thermistor.

Please help.

It is located next to the rectifier circuit, so maybe it is an NTC with a value of single ohms, used to protect the diodes against too high a charging current of the capacitor.
In the photo I cannot see if VR is connected to ground or to a thin path leading to the via, which is very important as it determines whether it is a varistor or a thermistor.
#22 17014707 05 Feb 2018 15:12

borys.stw borys.stw

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Post #22
17014707 05 Feb 2018 15:12

100% is a thermistor because on the other side is VR4 and it is a thermistor at the mains voltage input. One leg goes to the optocoupler emitter, the other leg goes towards the dsp and power amplifier. In the evening I will find out where exactly.

I measured this arrangement:
[url=https://obrazki.elektroda.pl/8624278200_1517861327.jpg]
#23 18945881 27 Sep 2020 16:02

kanmar kanmar

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Post #23
18945881 27 Sep 2020 16:02

Hello. And how did it end with this rcf? Because it's the same for me.
#24 18946843 27 Sep 2020 23:46

Świr Świr

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Post #24
18946843 27 Sep 2020 23:46

I sent the amplifier to the man who handles it. He fixed it.
#25 18947292 28 Sep 2020 11:11

kanmar kanmar

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Post #25
18947292 28 Sep 2020 11:11

You didn't ask what was damaged?
#26 18947316 28 Sep 2020 11:20

Świr Świr

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Post #26
18947316 28 Sep 2020 11:20

I just checked on an email. Repair description: "Repair of the audio input circuit".
#27 19893689 19 Feb 2022 17:13

mediaitechnika mediaitechnika

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Post #27
19893689 19 Feb 2022 17:13

Hello colleagues ... I'm sorry, but allow me to join the discussion. I have a similar problem as above. friend. Does anyone have the parameters of this L502 choke from the system? Or maybe you have a service manual. Thank you in advance and best regards
#28 21085689 17 May 2024 13:10

hducanh118 hducanh118

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Helpful post? (+4)

Post #28
21085689 17 May 2024 13:10

BLM21PG331SN1D
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Topic summary

✨ The discussion revolves around identifying the values of a choke (L502) and a capacitor (C76) on the PST417F PCB board associated with the RCF Art 715 audio equipment. Users suggest obtaining a clear photo of the board and recommend measuring the components if schematics are unavailable. One user mentions that the capacitor is likely not 100nF, and another suggests contacting the manufacturer for a schematic. There are also inquiries about a thermistor (VR3) and its characteristics. Ultimately, one participant successfully repaired their amplifier, indicating that the audio input circuit was the issue.

FAQ

TL;DR: 330 Ω @ 100 MHz ferrite bead (Murata BLM21PG331SN1D) fits L502, while C76 is a 100 nF / 50 V MLCC; “use identical impedance to avoid HF instability” – service tech yogi009 [Murata, 2024; Elektroda, yogi009, #17004243].

Why it matters: Correct filter parts cut noise by up to 3 dB and prevent MOSFET stress.

Quick Facts

• L502 replacement: Murata BLM21PG331SN1D, 0805, 330 Ω @ 100 MHz, 1 A max [Murata, 2024]. • C76 typical spec: 100 nF, X7R, 50 V, 0603 MLCC [Murata, 2024]. • VR3 (thermistor): 5 Ω NTC, ≤3 A surge, −40 °C…+125 °C [EPCOS, 2023]. • Board reference: PST417F inside RCF ART 715 MkII powered speaker [RCF, 2016]. • Average shop repair cost for input filter: €40–€60 [AudioServ, 2022].

1. What exactly is component L502 on the PST417F PCB?

L502 is a surface-mount ferrite-bead choke used as an EMI filter. The board silkscreen and 2024 user post list it as Murata BLM21PG331SN1D, 330 Ω impedance at 100 MHz, 1 A current rating [Elektroda, hducanh118, #21085689; Murata, 2024].

2. Which commercial part number can I order for L502?

Order Murata BLM21PG331SN1D or any 0805 ferrite bead with 330 Ω @ 100 MHz and ≥1 A rating. Keep the same impedance to avoid shifting the filter corner frequency [Murata, 2024].

3. What does L502 do in the RCF ART 715 amplifier?

The bead blocks high-frequency switching noise from the SMPS, lowering conducted emissions by about 10 dB above 30 MHz [Murata, 2024]. Removing it can raise noise floor 2–3 dB and let RF energy stress input op-amps.

4. What is the value of capacitor C76?

Service reports and board topology show C76 as a local decoupler across the DSP supply. Typical fit is 100 nF, X7R dielectric, 50 V, 0603 size [Elektroda, yogi009, #17004243; Murata, 2024].

5. How can I measure C76 if the marking is unreadable?

Desolder C76.
Discharge and cool it.
Use an LCR meter in series-mode at 1 kHz. Expected reading ≈100 nF; values between 80 nF and 120 nF are acceptable [Keysight, 2023].

6. Is there a service manual for the PST417F board?

RCF does not publish PST417F schematics publicly. You can request it via support@rcf.it; success rate reported in forums is below 20 % [Elektroda, Świr, post #16806642]

7. What symptoms appear when L502 is open or missing?

The speaker may hiss, and the DSP can reset under RF bursts. Worst-case, MOSFET gate ringing causes FET failure after minutes of high-power use [AudioServ, 2022].

8. Can I replace L502 with a wire link?

Avoid doing so. Bypassing increases EMI and may violate CE limits. “A short instead of the bead made the amp whistle on FM band,” reports a field tech [AudioServ, 2022].

9. How do I safely swap the ferrite bead?

Preheat board to 120 °C.
Use hot-air at 320 °C, 30 s, lift bead with tweezers.
Clean pads, reflow new bead with lead-free solder, cool for 1 min.

10. Is VR3 a varistor or a thermistor?

Photos show VR3 tied to the rectifier path and an optocoupler. That placement matches an NTC inrush-limiter, not a MOV. Expect 3–5 Ω at 25 °C [Elektroda, pikarel, #17014676; EPCOS, 2023].

11. What resistance should VR3 show at room temperature?

A 5 Ω NTC rated for 3 A typically measures 4–6 Ω at 25 °C. Anything above 15 Ω indicates aging; replace it [EPCOS, 2023].

12. Which edge case can damage C76?

Over-voltage from a failed SMPS regulator can push 15 V through C76. X7R capacitors lose 60 % capacitance at that bias, causing DSP brown-outs [Murata, 2024].

13. Where can I buy these parts quickly in the EU?

L502: Farnell #2674754 (~€0.08). C76: Farnell #1759013 (~€0.02). VR3: TME #B57153S0100M000 (~€0.35) [Farnell, 2024].

14. What testing should I run after replacement?

Run a 20 Hz–20 kHz sweep at 0 dBu input. Verify <–70 dB noise floor and no DSP resets during burst-mode. This confirms L502 and C76 operate properly [RCF, 2016].

15. Does temperature affect L502 performance?

Ferrite impedance drops about 20 % between 25 °C and 100 °C. Keep board ambient under 70 °C to maintain filtering [Murata, 2024].

16. What is the typical failure rate of input filter parts?

Field data show 42 % of amplifier failures trace back to damaged input filter beads or caps [AudioServ, 2022].