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Identifying polarity on a PCB for an electrolytic capacitor

by Poppycott / November 30, 2017 6:33 AM PST

A 10 Mfd 16v SM capacitor has broken off an un-marked Denon AVR-1912 HDMI B'D How can I tell which connection is NEG? Would it be the one with least resistance to GND?

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With rare exceptions.
by R. Proffitt Forum moderator / November 30, 2017 6:46 AM PST

You are right.

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Identifying polarity on a PCB for an electrolytic capacitor
by Poppycott / December 1, 2017 5:12 AM PST
In reply to: With rare exceptions.

I have now identified the microscopic (+) on the Cct Diag. of the HDMI for the Denon AVR-1912, the Service Manual, page 126, Schematic Diagrams (21/26) HDMI Unit (10/13) in a pdf from Denon. The Electr.cap. is No.C831, in-line, terminating at [ADINL] TO DIGITAL CNT Though the specified cap is a 10Mfd. 16v. I could only source a 10Mfd. 50v. - which should be OK. - though it isn't an SM so I shall create an insulator disc and eventually solder and hot glue it in place.

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That's a bulk capacitor.
by R. Proffitt Forum moderator / December 1, 2017 7:16 AM PST

At that size it's some power filter function so you could be 20 per cent off on capacitance. It's always legal to go higher on the voltage rating.

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That's a bulk capacitor.
by Poppycott / December 3, 2017 1:18 PM PST

Thanks for your identification! My purpose is now to trace the 'open' in the Signal conductors for the L channel and, looking at the Cct. Diag. p.126 of Denon AVR-1912 E2 EA , the top two ccts. on that page which use Op.Amps (I think) ID'd as IC27:A which terminates in a connector: 'TO DIGITAL CNT' as: [ADINR] and IC27:B which terminates in that same connector as: [ADINL]. The 'open' is in the (L) channel. With two tones being injected into AUXL and AUXR only the R channel gets as far as the FRONT R SPKR connectors on the back panel and can be traced with my audio amplifier and probe from C799 (the equivalent 'bulk' capacitor to C831 in the L channel) to its connector [ADINR] . Now I need to trace back the L channel and find out where the other tone stops. I am using a couple of audio generators injecting two different frequencies into AUXL and AUXR on the front panel. I referred to what I think are Op.Amps IC27:A in the R channel and IC27:B in the L channel. I cannot identify them in the Parts List on page.188 for there are no components between IC25 and IC28. I simply cannot find these Op.Amps on the HDMI B'D. . . . . HELP! What do they look like? Can anyone confirm that they are Op.Amps? Michael UK

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Sorry but
by R. Proffitt Forum moderator / December 3, 2017 1:33 PM PST

I don't see the IC in question by part number so I can see what I can find on google.

While I am an electronics designer, I know that if the device is too cheap, we replace the board or device. Board level repair is for those that want to go there. Your cap replacement looks fine to me.

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That's a bulk capacitor.
by Poppycott / December 4, 2017 7:21 AM PST
In reply to: Sorry but

Thank you for your input. I would like to add some information following further examination of the layout in the Cct.Diag. of these IC's. There are ten of these 'four-contact' IC's in the form of a triangle (= Amplifier?) and they go in pairs. The 1st of a pair is given contacts 1,2,3,4 and the 2nd is given contacts 5,6,7,8. The 1st pair are not given an I.D., but the remaining pairs are: Pair 2: (IC28:A&B) A=[FL] B=[FR] Pair 3: (IC31:A&B) A=[CEN] B=[SW] Pair 4: (IC32:A&B) A=[SL] B=[SR] Pair 5: (IC34:A&B) A=[SBL] B=[SBR] Looking at the back panel, the letters in the square brackets are the Speaker Channels: Front R, Front L etc. So it would seem that each of the five Op.Amps (if such they be) are divided and I should be looking for 8-pin IC's somewhere. Also, the 1st Op.Amp triangle points from page R to page L., whereas all the remainder point from page L to page R. Is this triangle showing the direction of the Signal? If Op.Amp. No.1 is faulty and it is an SM component I have a Hot Air soldering gun which can de-solder it for replacement. Getting a replacement pcb for this Denon AVR-1920 is not an option. If it cannot be repaired the entire Unit is 'toast' Michael UK.

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That's a bulk capacitor.
by Poppycott / December 4, 2017 7:31 AM PST

In my last post I gave the wrong Model number: it should be Denon AVR-1912 (not 1920!) sorry! Michael UK Ought I to changing the title of my posts? We are discussing the Op.Amps in the HDMI B'D now, not the Bulk capacitor! Michael UK.

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When that happens we shop for replacements.
by R. Proffitt Forum moderator / December 4, 2017 7:48 AM PST
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When that happens we shop for replacements.
by Poppycott / December 4, 2017 8:22 AM PST

Thank you for your very helpful reply. Being retired I can (possibly) afford replacement components but not the whole unit and my time is 'free' - and I would like to gain experience in identifying causes of problems and repairing pcb's. What I am therefore doing is finding my way through the relevant Cct. Diags and trying to identify not only 'what' the various components are (and their correct names) but where they are and what they do and just what is that IC27:A & B which is not included in the 'List of Parta'.  Any help is greatly appreciated! About four years ago I dis-assembled my AKAI GX-635D NAB tape deck which had ceased to function  and replaced all the 'front-end' transistors and electrolytics in it with help from Forum members. This was a great success! Quite a learning curve for one who started building Crystal Sets and remembers the 'brou-ha-ha' surrounding the invention of the 'Transverse Resistance'! Michael UK

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Best of luck.
by R. Proffitt Forum moderator / December 5, 2017 7:22 AM PST

You have the time, and here I see a 20 dollar donor machine.

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When that happens we shop for replacements.
by Poppycott / December 5, 2017 6:08 AM PST

I have just removed the HDMI B'D and searched for IC27. The HDMI B'D is a two-sided board with components on both sides. There is a place for the IC27, but it has never been fitted. The B'D shows the number IC27 AZ4580 next to the 8 pre-soldered pcb contacts - but no actual IC has ever been installed. Therefore my Cct. Diag drawings are not for this particular model which, on powering up in 'Special Mode Setting' by pressing 'Start UP' button together with 'Status' & 'IPOD' buttons (under the screen) at the same time (briefly) followed by pressing the 'Status' button a second time shows this version of AVR as: 1912 E2/EA . Now we know. The other four IC's, fed from the 48pin AK4358VQ (IC29) before being Digitized, are Dual Low Noise Op.Amp. AZ4580's. So there's no Op.Amp to consider as having a problem in the VAUX channel. I must look elsewhere.  Michael UK

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