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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    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. wurlyman

    wurlyman Active Member

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    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
  15. wurlyman

    wurlyman Active Member

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    Hey guys,
    Mark Walker in N.C., AKA Blueglow Electronics just showed a new product in his latest video that lets you watch a circuit in action and on a virtual oscilloscope. I see all kinds of possibilities with it. I'm a visual learner and this looks great. Everycircuit.com
     
  16. wurlyman

    wurlyman Active Member

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    207
    Location:
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    OK, I've rebuilt the P800 power supply after blowing C803. Replaced the H808 and 809 with Common cathode rectifiers MUR1620 plus C804, C806 and C811. Replaced transistors H803 thru H807 with KSC 2383 and matched the pairs, checked the 4148 diode at H812 and H801 and H802. Everything looks good. Waiting for my friend to come over for a test again. _DSC0285.JPG
     
  17. wurlyman

    wurlyman Active Member

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    Location:
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    Spent a very productive evening re-testing. The P800 power supply, PE01 tone and pre-amp and the right channel amp P700 are working fine. We even played it through a speaker, what a great feeling to hear it again after seven months and knowing that I did that! We set the DC voltage on the power supply to 35 volts and checked the 19 volt and 14 volt pins. They were within tolerance and that was with a 100 watt dim bulb. We will re-check it when the whole rig is completed.
    Left amp has no sound so we've pulled it out, found one broken wire which may have happened after we pulled it out. Did a little non-power testing of components including the differential pair and all diodes but haven't found the problem yet. I'm going to put some extensions on those wires that go from the output transistors to the jacks and take some of their tension off. Did about an hour's worth of HD videos of the process. All in all, it was a good night.
     
    Last edited: May 18, 2017
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  18. wurlyman

    wurlyman Active Member

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    Here's a follow up photo for those of you who wondered if the parchment paper instead of velum would work. I used it and blue LED fuse type lamps. The indicator lamps are still original. It looks great and I love it! _DSC0287.JPG
     
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