On Going Saga of 2325 re-cap and restore

Discussion in 'Marantz Audio' started by wurlyman, Apr 26, 2017.

  1. wurlyman

    wurlyman Active Member

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    I'm a noobie, learning as I go. I started this project last October and just did my first 'smoke' test a couple of weeks ago. Wasn't disappointing, got the smoke. Found out that you CAN test the receiver without connecting the two amps so the only parts I was testing that were reworked were the Power Supply P800 and the Tone and Pre-Amp PE01. The problem was in the P800 power supply. Here's a tip for other beginners. We ran the dim bulb tester plugged into a variac and a DMM connected to the main caps so we could see the voltage come up. Everything looked fine with a 60 watt bulb, then switched to a 150 and at full voltage the 470 uf cap, C803 smoked and started to bulge. Here's why. I had replaced the two rectifiers at H808 and H809 with MUR1620 To220. What I hadn't learned yet was those are available in both Dual Common Anode or Dual Common Cathode and the only difference is one letter in the part number, nobody mentioned that. I didn't even know what those terms meant until last week. Of course, I ordered and installed the wrong one which made the polarity of that cap reversed. In the photo of the schematic below you see the two diodes in the rectifier connected together with their Cathode ends. If the diodes had been pointing in the opposite direction they would have been Common Anode.

    _DSC0267.JPG
    This post will continue and I'll always try to keep the beginners in mind when explaining things. I'm especially grateful to Steven Tate, Catrafter, rBuckner, MBuras, John of KT, and of course Leestereo.
     
    Last edited: Apr 26, 2017
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  2. paul_ral

    paul_ral Active Member

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    These diodes have engraved symbols on the body
     
  3. Bert 1100

    Bert 1100 Super Member

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    Ouch....and the 2325 is not exactly a receiver to learn on....
    Hopefully nothing else was damaged.

    Good luck, I'll be following since I have a 2325 coming in soon !
     
  4. wurlyman

    wurlyman Active Member

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    Actually they are rectifiers and if you don't know what you are looking for or the difference between common anode and common cathode the symbols mean nothing. The 2325 is my only receiver, had it for over thirty years plus it cost me nothing. I want to do this just to be able to say I did it. At 75 I've done most everything else. The good news is I'm not flying blind. An old friend of mine was the tech at a recording studio I worked for in the Seventies. We have re-connected and he's now the head chair of Solid State Circuits at Cal State University here in Sacramento. He does the hiring and sets the curriculum for the professors in the electronics department. He's agreed to oversee my work and guide me along the way. I'm trying not to bother him too much but he will come over for tests and bring a scope with him. I feel pretty secure.
     
  5. wurlyman

    wurlyman Active Member

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    The MUR1620's are not engraved. They have the number stamped on them and KAK. The original rectifiers did have the symbols pressed into the black plastic body but you'd never see it if you weren't looking for it. Took a jewelers loop just to see it.
     
  6. Steven Tate

    Steven Tate AK Subscriber Subscriber

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    This is good information. Thanks for posting! :thumbsup:
     
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  7. wurlyman

    wurlyman Active Member

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    _DSC0090.JPG _DSC0094.JPG
    Here's the PE01 board with and without tatalums

    Today's topic is Tantalum capacitors, all of you with experience feel free to join in. These are the little blue pea sized capacitors you will find on some of your boards. Most of the people I've followed here and other places are vehement about replacing these either with electrolytic's or films and I dutifully did that on the P700 amps (1) and the PE01 tone board(6). Now, I'm not so sure.
    I bought a wonderful book called How To Diagnose and Fix Everything Electronic by Michael Jay Geier. The title is a little misleading. He doesn't explain how to repair every electronic product (in a way he does) but the main focus is understanding parts, how they work, what goes wrong with them and how to diagnose and repair or replace them. He also covers tools and workbench, how to use an oscilloscope, interpret schematics and diagrams and much more. An excellent read that I highly recommend. It's also available as an E book.
    Concerning tantalum's he writes "Tantalum capacitors should always be replaced with the same type. They have lower impedance at high frequencies than do standard electrolytics and are used only where that matters. Replacing a tantalum with a garden-variety electrolytic will result in performance degradation or circuit failure. The capacitance tolerance of tantalums is much tighter than that of standard electrolytics, so use a part with the same value. An increased voltage rating is fine, however."
    I'm interpreting that to mean, since six of the tantalums were in the tone/pre-amp board, that tantalum circuit allows more of the high frequencies to get thru. That is obviously why Marantz chose to use them, I'll bet it had nothing to do with economics. I have seen threads on this forum where people have said the high end seems muffled or the highs aren't there, this could be your answer friends. I tested the old ones last night and two of them had rather high Equivalent Series Resistance, one was 6 ohms and the other was 8. I checked Mouser last night and the tantalums are readily available and I think I'm going to buy new and replace them.
    Any thoughts from you old pros?
     
  8. SaturationPt

    SaturationPt AK Subscriber Subscriber

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    I've designed many (production) analog and digital electronics / circuits in my former career and I too get irritated by all of the "re-cap is the best thing you can do, up-rate voltages, up-size power supply electrolytics, don't worry about ESR and other silly specs what you buy is close enough if it's Nichicon Audo, ...". Even using transistor substitutions has its risks.

    I have always designed my circuits and selected the components based on the best specs for the application, and meeting the environmental needs, never less. I feel confident that Marantz, McIntosh, Pioneer, Yamaha (etc.) did also in this era and any change that you make deviates from the design.

    Yes there were some components that failed over the 40-years that these units have been out, and certainly the technology has evolved to produce capacitors etc., but if you can find exact replacements use them unless there is a known failure or you're an Engineer with audio experience and are able to ask the designer why he used the components that he did.
     
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  9. Steven Tate

    Steven Tate AK Subscriber Subscriber

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    Not an old pro here, but I would bet that by referring to high frequencies, he wasn't referring to 20khz. Anything in the audio range is low frequency in the electronics world. I have replaced many tantalums with WIMA films and have always found my total rebuilds to be brighter than when I started. I'm not saying it was just the tantalums. I'm just saying that replacing tantalums with film capacitors is not going to degrade the higher audio frequencies based on my listening experience. Here is the PE01 board I did in my 2325 and it sounds so good it nearly brings me to tears. :biggrin:

    [​IMG]
     
    Last edited: Apr 27, 2017
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  10. wurlyman

    wurlyman Active Member

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    Steven,
    I used the electrolytics for the 3.3 ohms and the films for the 1.0's as you can see by my above photo. Do you think I'll have a problem with that? - Stu
     
    Last edited: Apr 27, 2017
  11. wurlyman

    wurlyman Active Member

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    129
    Location:
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    Thanks for the reply Jeff. I have upped the voltage on almost all of the caps; 10 to 16, 16 to 25, 63 to 100 etc but never the value. See my next submission on transistors. - Stu
     
  12. Steven Tate

    Steven Tate AK Subscriber Subscriber

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    I doubt there will be audible difference either way. I know mine sounds great, but there are lots of components besides those caps. That board is pretty easy to remove. This might be a good place for a comparison -- listen to it the way you have it and then change those two caps to films and see if you can tell the difference. Or even go to all four tantalums or electrolytics and compare. It would be interesting, but I'm betting you wouldn't be able to tell the difference.
     
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  13. wurlyman

    wurlyman Active Member

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    Next: Transistors,

    One of the 'pros' who used to post here suggested that the five transistors on the P800 power supply, H803 thru H807 be replaced with KSC-2383Y. When I asked him how three different transistors (two pairs and one odd ball) could be replaced by the same transistor he blew me off saying he was educated and I should have sent the machine to him and quit messing with it. WRONG ANSWER! So, I did the replacement but have just found a trans substitution site and that transistor doesn't match any of the three. Now, I either put the old ones back (two of them test bad) or pick something off of the substitution list. The old ones are 2SC734 R.O.Y. ; 2SC945 Q.R ; 2SC1318 P.Q.R. Jeff, I'd love to hear your response to this?
     
  14. Trojan4Life

    Trojan4Life Active Member

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    I'm old, so I'm old school, don't claim to be a pro audio tech. However, being that I'm old, I come from the school of not fixing it if it ain't broke- especially with regards to transistors. If your super engineering/tech/teacher wants to teach you about matching beta, Vce, building and using a test setup to check Vce, or better yet a curve tracer, then go for it. Maybe you have a curve tracer or have built a test setup for measuring Vce?

    Transistors are funny little fellas. They can test good with a DMM on diode test mode, but break down (leak) under operating voltage/current, which you may not see unless you test them with a curve tracer. The shotgun method of simply replacing transistors when they don't need to be replaced might introduce a lot of other problems, especially when/if you've got a differential amplifier pair (which I believe the model 2325 does have).

    Learn how to match beta if you really feel the need to change the transistors. Hopefully your friend has a curve tracer and can teach you how to use it to test and match Vce for the differential pair.

    I got the same answers when I was repairing my 1200, was advised to send it across the USA for repair, blah, blah, blah. It just made me want to learn more and challenged me to repair the amp. It took me about 3 months, (mostly waiting for parts, some I didn't need), but I accepted the challenge and am listening to the unit as I type.
     
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  15. wurlyman

    wurlyman Active Member

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    129
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    Thank Trojan4Life, I'm jumping thru the same hoops, just got another shipment of parts I'm not going to use, but I'm determined to do this. My DMM has Hfe test on it, so I'm pretty sure I can match pairs or multiples. Two of the old transistors did test bad which is probably why my tuners both quit and the reason I started the project in the first place. The rest of the receiver worked just fine. I can find NO replacement for 2SC734Y. I'm old too and right now I'm motivated to curl up and sleep.:boring:
     
  16. Trojan4Life

    Trojan4Life Active Member

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    Hello Wurlyman-- My first stereo system was a Sansui AU-719 and TU-717, they were purchased new when I was in Japan, serving as a avionics tech. They didn't have a schematic, (anyway I don't remember there being a schematic). The Marantz units came with a schematic and service manual, not that they are the greatest, but at least you could work on them. I've also read that there were details/information the Marantz service manual didn't print but taught their factory service reps so that it made the Marantz units somewhat un-fixable by the average Joe.

    All these years later, I had to relearn about differential amplifiers, (commonly called diff pairs on AK), how to find a replacement transistor because when we were deployed back then, we didn't have CDs with schematics/service manuals and the internet. It wasn't until I was well into my 30s that the inter web, pagers, cell phones, fax machines and all those things my son never knew didn't exist until the 1990s. So, I did a search for 2SC734Y and found this posting: http://audiokarma.org/forums/index....-5v-instead-of-35v.172803/page-2#post-1981362

    It says that the 2SC734Y equivalent is: Fairchild BC182L and a Mouser part number. I looked at the Mouser part number and found that it not available- at Mouser anyway. However, posting #22 says:

    "For H806, (This is me talking: I believe that's the 2SC734Y you are looking for? If not, the following information is useless, but you can use the AK search function), you need a high DC gain transistor for this application, for good regulation.

    After further searching for your substitute, yes the 2SC1567 will work. It is a 1.5W transistor. Better than the original."

    Being that I love the inter webs, I did a search for 2SC1567. Mouser doesn't have it. Newark Element 14 didn't have it, but Little Diode does. www.littlediode.com

    Be aware that Little Diode is across the pond (those guys we fought a War of Independence and beat), and because the British pound is worth more than the US dollar (the sun never set on the British Empire at one time), you'll pay more and have to wait a while longer. Remember I told you that I spent 3 months repairing my amp? Most of the time was waiting for parts.

    Being the wiley old guys that got us this far in life, all is not lost! (I always tell my 24 year old that old guys rule). Mouser has this little tab that says show similar:

    Screen Shot 2017-04-27 at 7.48.24 PM.png

    There are a plethora of similar transistors. You can use the "filters" on their website (and Newark and Digikey for example, I'm not endorsing just Mouser, I've never had any problems at all with any of these vendors), look at the data sheets and find one most similar to the TO-92 package/case style, NPN, Collector-Emitter Saturation Voltage (Vce), Beta (hFE), voltages and fT.

    BTW- the Vce value is very important with regards to the differential amplifier pair. Read up on it and ask your CSU friend if he has access to a curve tracer. You should also learn how to check the base and emitter voltages, being aware that some transistors might have a different pin-out configuration other than EBC.

    These are a few of the things that the techs do and know and why you pay them if you don't want to learn how to DIY. I'm not trying to take work away from someone trying to make an honest living, but I wouldn't enjoy a life without music and just enjoy the DIY aspect of electro-mechanical troubleshooting and repair.
     
  17. Trojan4Life

    Trojan4Life Active Member

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    398
    Using Mouser's filters for through hole, TO-92-3 package :

    Screen Shot 2017-04-27 at 8.12.19 PM.png

    Choosing 60 V for VCBO value leaves you with about 15 choices Mouser has at stock and the most expensive is a little over $1.00 US. They have thousands in stock. I ordered on a Monday morning, had the parts via USPS by Wednesday.

    Anyway, download the data sheets, buy a bunch and match beta (hFE, gain) with your meter, solder them to your board and go back to listening to music.
     
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  18. wurlyman

    wurlyman Active Member

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    Thanks for this Trojan4Life. Great information which I'll put to good use. No, the 2SC734Y is for H803, only uses one transistor of that model. The other two are 2SC945Q.R. and 2SC1318P.Q.R. and they are pairs. I've already Hfe matched and done the two differential pairs on the P700 amps. Take a look at my schematic of P800 at the top. Are H806 and H807 what they call a Darlington pair? The emitter of 806 feeds the base of 807. Just curious. Hadn't heard of Newark, got to check that out.
    Most of the transistors have a pinout of ECB on the Marantz boards and that seems to be the most common. That's true on everything I've bought so far except the To-220s which are BCE.
     
    Last edited: Apr 28, 2017
  19. Trojan4Life

    Trojan4Life Active Member

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    Sure looks like a differential pair to me...

    Screen Shot 2017-04-28 at 11.34.32 AM.png

    You can also call Mouser, Digikey, Newark, etc. tech support and ask them if they can help you find a substitute.

    I see the voltages listed below each Q, do you have some probes and a meter to check for the proper voltages? I'm not advocating changing transistors if they test good.
     
  20. Trojan4Life

    Trojan4Life Active Member

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    Also, are you aware that irebuildmarantz.com offers a kit for the 2325?

    I've never rebuilt a Marantz receiver, but from reading the website, it looks like he will answer questions, especially if you are using one of his kits.

    This is probably the route I would go if I were to rebuild one of these receivers, just because it would save me some time and I'm more into listening to these units, rather than rebuilding them.
     

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