Another 2285B, this one has problems.

Discussion in 'Marantz Audio' started by 1978_DREAMER, Jan 29, 2018.

  1. 1978_DREAMER

    1978_DREAMER AK Subscriber Subscriber

    It's been quite a while since I've posted and now I have a new project. A fellow AK'er offered me a 2285B with the left channel not working after he followed my re-cap and binder post project. Eventually I accepted the conditions and now I'm finally digging into the first of a couple of issues. The left channel has little to no audible output. This unit has been re-capped and I find additional repairs made to wire connections, it's also seen a rough life but most everything is in-tact. I started by repairing a couple of cold looking solder joints and I thoroughly cleaned all the switches with DeOxit and the power supply board that had excess scuzz on it. I fired it up using my dim bulb tester and on separate occasions I was not able to get DC Offset & Bias adjusted then I did and now I can't. I started tracing some of the wire repairs and I ran into these connections to the Pre-Out and Main-In RCA terminals. Are these correct? I'm having trouble getting this to work in my mind since plugging anything into the Main-In will disconnect the Pre-Out. I don't know which wire posts are switched and which ones are not to get the initial connections and jumpers in the correct places.
    It's good to be posting again!
    Jerry
    20180129_070423_resized.jpg 20180129_070435_resized.jpg 20180129_070614_resized.jpg 20180129_070423_resized.jpg 20180129_070435_resized.jpg
     
    Last edited: Jan 29, 2018

     

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  2. 1978_DREAMER

    1978_DREAMER AK Subscriber Subscriber

    OK guys you're off the hook. I isolated the RCA connectors and inserted a patch cord into each one individually then tested for switched and non-switched posts. These are wired correctly when compared to the schematic. NOW, #2, an electronic component question that I'm having no luck researching. On the Pre-Amp board there are 4 components that appear to be 5 pin double transistors on the schematic. What is the correct name for these? There are voltages specified for each leg and I intend to map out the required vs actual readings on these and the transistors. Are these no load values and if not how do I load the circuits?
     
  3. catrafter

    catrafter Marantz Specialist Subscriber

    Messages:
    6,083
    Location:
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    Those 5 pin devices are 2SA798, they consist of two PNP transistors in one package, the emitter on both transistors share one connection.
    A quick search turned up several threads here on AK about them.

    Usually, the voltages listed on Marantz schematics are DC, referenced to ground (the chassis) with no signal applied. The exception is in the tuner, IF and MPX areas where they are sometimes with/without a strong station or strong stereo station tuned in.

    Tom
     
  4. 1978_DREAMER

    1978_DREAMER AK Subscriber Subscriber

    Thanks Tom!

    After my last post I continued to research those dual transistors and found that they were Monolithic Transistor Pairs. It got a lot easier once I added the 2S in front of the search.

    I really appreciate your information on the DC voltages. I planned on testing voltages relative to the ground bracket near the big caps and I was concerned about needing a load or not.

    Once I get the left channel back I'll need to address a non-existent FM signal.

    It's good to see your response. My personal unit that you helped guide me on the re-cap still sounds great! Many, many thanks!

    Jerry
     
  5. Jailtime

    Jailtime Standin' on a corner Subscriber

    Messages:
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    Those 2SA798s are junk. Both of them had failed in my 2216B, causing spitting and popping on the outputs. They have a bad reputation, so they were the first thing I suspected.

    I used a gain matched pair of KSA992 to replace them, watch your pinouts.
     
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  6. 1978_DREAMER

    1978_DREAMER AK Subscriber Subscriber

    Thanks Jailtime! It's good to hear from you also! Thanks for the heads up.

    This is a good unit for me to improve my electronics skill set, which is really minimum. I'll test voltages then I may just shotgun these and see how I do.
     

     

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  7. 1978_DREAMER

    1978_DREAMER AK Subscriber Subscriber

    Well I'm making progress. I measured all the voltages on each single and paired transistors on the Pre Amp board. The voltages were off as much as 2 volts on some but both channels had balance and none of them were flat out failed. I'll address those once I get everything functioning. While I was messing with that board I re-cleaned all the switches then cleaned both sides of the board which took off more gunk. Still no left channel. Next I carefully pried open the speaker relay and revealed 2 blackened contacts. I cleaned all 4 pairs with an India stone then burnished and finally DeOxit. With the cover back on I tested the unit with my DBT supply. Success! The left channel returned. Now off to the FM board. I've already identified one non-soldered leg on a cap.
    Jerry
     
  8. 1978_DREAMER

    1978_DREAMER AK Subscriber Subscriber

    OK, progress just stalled. I let the receiver run for a while and the left channel started to make a periodic popping noise and I don't have much power. As noted before I cannot get offset or bias voltages to register.

    I did measure no load voltages for each transistor on 3 boards. Each test yielded some reading. The Main Amp is really bad based on the tested values. I put together a spread sheet and here is a jpg version and there is a pdf attached of it. I think I should be able to share it through a PM if needed in the Excel format.

    transistors pg 1 of 2.PNG


    transistors pg 2 of 2.PNG

    2018-02-04_component tests, in or out of circuit.pdf

    I need to start putting together a part order. I need mica's and thermal grease for sure and I'd like to add some transistors to the list. This unit was re-capped with ELNA SILMIC II's so for now since none of them are visible problems I'm going to leave them alone.

    If any one sees a good starting point for me based on these measurements then I'm all ears.

    Jerry
     

    Attached Files:

  9. Jailtime

    Jailtime Standin' on a corner Subscriber

    Messages:
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    Have you used the main in/pre out jacks to isolate the channel dropping to one of those sections?
     
  10. rBuckner

    rBuckner Luv 2 Restore Subscriber

    Messages:
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    Impressive spreadsheet! Good to see you back. On the thermal grease make sure to NOT get the silver / conductive computer CPU type stuff.
     
  11. 1978_DREAMER

    1978_DREAMER AK Subscriber Subscriber

    Hi Jaltime, I did get the left channel back by cleaning the relay contacts. As far as isolating my low volume output I have not isolated the signal using those jacks. I'll test that. In my mind's eye I don't see a correlation back to the pre-amp for my lack of getting offset or bias readings that's where I started testing voltages at each transistor. Now the popping that I'm getting in the left channel could well be those transistor pairs on the pre-amp and I intend to swap those out.
    Thanks,
    Jerry
     

     

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  12. 1978_DREAMER

    1978_DREAMER AK Subscriber Subscriber

    It's good to be back! It's burning some brain cells since I'm not skilled in electronics but I find it to be very compelling work. I am starting research on transistor replacements and that will be added to the spread sheet and I'm thinking about adding each transistor from the part list in the service manual. Kind a one stop shop that can readily be updated. I may even tie in my cap list from last time if I get it correct.
    Thanks for the note on the grease, I've been doing a lot of reading through Ecowars' posts on the subject.
    It has been a while, is your Avatar photo a current companion? I remember you going through a tough transition back then...
    Jerry
     
  13. Jailtime

    Jailtime Standin' on a corner Subscriber

    Messages:
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    Location:
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    OK, I'm tracking now, couple different problems you're having. You said in the first post that you were able to get bias and offset adjusted, but intermittently? Might be worth a try to swap out the trimmers for those adjustments. Just a thought.
     
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  14. rBuckner

    rBuckner Luv 2 Restore Subscriber

    Messages:
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    Yep, ole Angus is getting older but is doing well enough. Damn arthritis is getting to the both of us these days!
     
  15. 1978_DREAMER

    1978_DREAMER AK Subscriber Subscriber

    New trimmers make sense to me. Is there a preferred source for these? I gave it a go on Digikey and Mouser sights and found these 201's in Digikey, they appear inverted compared to the Marantz 202's for the 1k ohm pots. I'm not having any luck finding the same mounting size 2k ohm pots with the 15mm width.
    CTS 201 TRIMMER POT, 1.PNG CTS 201 TRIMMER POT, 2.PNG CTS 201 TRIMMER POT, 3.PNG
    Any help would be appreciated.
     
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  16. Steven Tate

    Steven Tate AK Subscriber Subscriber

    Messages:
    2,680
    Location:
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    A lot of people prefer Bourns multi turn trimmers because they aren’t so touchy when setting. Something like this, although I’m not sure it’s the exact one you need. This is the vertical adjustment screw version. There is also a horizontal screw version. I would definitely use the 3/8” 1/2 watt version rather than the 1/4” version. There is also a version with the three terminals in line instead of staggered.

    https://www.mouser.com/ProductDetail/Bourns/3296Y-1-202LF?qs=/8Tj2/Bce9Zv0b1Osh/38w==
     
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  17. 1978_DREAMER

    1978_DREAMER AK Subscriber Subscriber

    Thanks for the comments Steven. I looked at those as an option but not being schooled in electronics I was concerned with what setting to start with and I didn't know if it is possible to bench set them before installation. This unit is not pristine so the appearance is not a concern as long as the pins line up reasonably without major alterations. I know that the existing ones have a 15mm housing width with pin separation probably 2-3mm less..
    Jerry
     
  18. 1978_DREAMER

    1978_DREAMER AK Subscriber Subscriber

    Hi guys, after replacing all the 2SA798s with pairs of KSA992s and replacing all 4 trimmers, nothing improved and I actually lost volume in both channels. While installing the KSA992 pairs I was super cautious to get the correct pin outs. I kept the old 2SA798s and trimmers which all bench test acceptable and can be reinstalled. I started looking for shorts and voltage readings before giving up for a while on it, a little deflated. Today I powered up through the dim bulb tester with the main amp pulled out to eliminate any influence from it. I was checking voltages again then powered down and bled down the big caps checking to see when they were safely drained. I noticed that one cap seemed low when I went to drain it so I powered back up and then down again and sure enough one out of all 4 caps drained down rather quickly all by itself. Is this a possible short that I need to find? One more thing, the previous speaker relay cleaning did not last very long and the left channel is out again. While I had it powered up I checked channel voltages coming out of the relay pins and the right one showed about 24V and the left one showed about 1v. I think the contacts have carbon-ed again so should I simply replace the relay or search for the cause of the failure? All help is always appreciated. Jerry
     
  19. Jailtime

    Jailtime Standin' on a corner Subscriber

    Messages:
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    Location:
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    Are the main filter caps in this receiver the originals? I looked at your spreadsheet again, the 52V rails are sagging pretty bad.

    I'm not clear on where you measured the voltages on the relay. Does the relay engage? What are the voltages on J815 and J816 if so? If not, what are voltages on J813 and 814?
     
  20. 1978_DREAMER

    1978_DREAMER AK Subscriber Subscriber

    This unit was re-capped before I received it. The main caps are all Nichicon KG(M) Gold Tune 6800 uF 63V.

    The relay voltages must have been coil readings when I look closer. J813, J814, J815 & J816 are all 1.08V, I didn't note +/-.

    I have been wondering about the transformer outputs but I haven't disconnected leads to evaluate.
     
    Last edited: Apr 15, 2018

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