1300DC on the Bench

Discussion in 'Marantz Audio' started by Fhamre, Mar 5, 2017.

  1. Fhamre

    Fhamre AK Subscriber Subscriber

    Picked up a nice 1300DC recently and today opened it up to see what if anything has been done to it and what parts I will need when I do a full blown restoration.
    Preliminary testing indicates only the right channel working. I do a quick cleaning of the accessible switches and the volume control.I then start to look for any signs of previous work in the amp section. I can see that someone has worked on the left channel. They replaced a power transistor A968B with a NTE 368. That transistor will have to go as its not up to spec and I hate NTE. I also have a A968B in my parts pile.
    Pulled out both amp boards to compare and check to ensure I have all the caps and trimmers I need.Unit has its original outputs,sweet.Noticed on the left channel that a bolt holding Q714 to the heat sink was literally flopping in place. It needed a small wrench to hold the nut while tightening the bolt. Hard to reach so I guess the tech wasn't in the mood.
    I plan to tackle the amp section first as far as recapping. Looks like I have all the small value caps including the axials for power supply and the relay( MY02-02).
    Put the driver boards back in for more testing and now have both channels working. Phono works as well but switches will need more cleaning. Will do that when I pull the pre amp section apart.That will be fun. Does anyone know a part number for the two small relays found in the pre section?
    I am no expert so always looking for advice. Anything I should be looking for? Failure prone components?
    Should I be doing all my testing AC coupled?
    Thanks in advance!
    IMG_6423.JPG IMG_6422.JPG IMG_6418.JPG IMG_6421.JPG
  2. Jailtime

    Jailtime Standin' on a corner Subscriber

    Velva ND
    Not many people get the opportunity to work on a 1300DC, cool amp! Are the relays in the preamp section those goofy reed type ones? Those can be a pain to source a replacement for.

    I think I did all the testing AC coupled when I had an 1180DC, not sure it really matters though.
  3. Fhamre

    Fhamre AK Subscriber Subscriber

    Not sure about the pre amp relays. Haven't pulled that section apart,yet. Tackling the amp section first.
    Looking for guidance on setting the bias. The service manual says set the left channel to 20mv the right 10mv.
    I just set it at 15mV for now. One channe,l the one previously worked on was 48mV. The right was at 22mV.
    Just want to have confidence in the amp adjustments before I go in and recap.
  4. Fhamre

    Fhamre AK Subscriber Subscriber

    Well I have gone through the 1300,replaced all the electrolytic' s,epoxy diodes,protection relay,glue and new thermal compound on all transistors with heat sinks.
    I will be ordering the power supply caps later. I opted not to replace the two reed relays. A suitable replacement is hard to source. However I did find in my relay supply some left over US relays that are apparently a great choice. However as these ones work fine I left them in. I'll save my no longer made reeds for a future project.
    I've added a few pics to show several different boards. I think you can tell which are before shots. Tearing apart the pre section is a bit intimidating. Lots of pics is the key.
    Still in the testing phase. Haven't put on the face plate.
    Overall not too bad to work on.One of the most tedious jobs was replacing all the old thermal compound on transistors mounted to heatsinks.
    1.JPG 2.JPG 3.JPG 4.JPG 5.JPG 6.JPG 7.JPG 8.JPG
  5. catrafter

    catrafter Marantz Specialist Subscriber

  6. Fhamre

    Fhamre AK Subscriber Subscriber

    Well just when I thought it was a done deal I discover I have lost the left channel in phono. Both channels were working before recapping.
    So it was so much fun the first time I went back in to check my work,resolder any suspects etc. including trace continuity on the phono board and opted to replace the relay while I was at it.
    Put it back together,same issue. Dead left channel.I am no Schematic wiz on a good day but the copy of the schem in the service manual pdf out there is a challenge to follow and read.
    I believe the left channel on the phono board is the portion I have identified in red in the first picture.
    I have taken some voltage readings of the matching channel components I can reach. I have included a picture to show where I have taken readings and where I think there are correct voltages (green -28V) and (red .9V)incorrect.
    I have tested all the transistors on the so called left channel including the FETs and they test fine.
    An issue with the relay or?
  7. Fhamre

    Fhamre AK Subscriber Subscriber

    Here's the phono schem.
  8. Fhamre

    Fhamre AK Subscriber Subscriber

    No one out there have any suggestions? I am going to take another crack at it tomorrow.
  9. Steven Tate

    Steven Tate AK Subscriber Subscriber

    N. Richland Hills, TX
    Any chance C418 is screenprinted backward? Everything on the board seems to be a mirror image except for C417/418. :dunno:

    Edit: Looking at schematic, they don't seem to be mirrored in the circuit - they are tied together, so it's probably right.
    Last edited: Mar 17, 2017
  10. Fhamre

    Fhamre AK Subscriber Subscriber

    Hope to try again,today. Just don't want to keep going in without a plan for success. One should try and minimize going into to this complex piece. It could lead to further frustrating issues.
    I was hoping some one with more savvy than me could chime in with the magic solution.Note phono worked before I went in and somehow lost a channel after the recap.
  11. Fhamre

    Fhamre AK Subscriber Subscriber

    Still scratching my head on this one. Went in again,replaced the diodes Q343 and Q436 even though they tested fine. I do note that I can see a L and a R marked on the board just by the right end of the relay.The channel I have lost is the left. I can't determine how this circuit works thus I can't seem to find the problem. I know it must be some thing simple.
  12. airtime

    airtime Super Member

    Central Arizona
    Stupid question, but did you check all the connections coming both IN and OUT of the board?

    Does that also you that crappy black ribbon connector wiring. If so LOOSE IT.
    KutzlerTrans likes this.
  13. Fhamre

    Fhamre AK Subscriber Subscriber

    Not a stupid question. The ribbon cables are just used to attach the left and right tone sliders. But there are no shortage of wires and connectors. I do my best to minimize flexing etc. and have tried to pay attention to possible issues as a result of going in so to speak.In the perfect world you should hopefully only go in once. That was the plan. So much for that. Now I am hoping I get some knowledgeable individual to come along who can shed some light on this circuit so it can lead to the issue. As I don't want to keep going in blind hoping to get lucky. I seem to be out of that.
  14. airtime

    airtime Super Member

    Central Arizona
    It looks like you are just going to have to trace the signal and find at what point it drops out.

    But DO start at the RCA input beginning and test the entire path.

    Is the signal getting to the board?

    I once had a unit that would work with the board out. Every time I put it in it would stop. I eventually soldered test wire lead long enough to test it while installed. turned out to be a loose input solder pad lifting off the board. Put the board in and the pad would lift. But that was my fix problem.
  15. Fhamre

    Fhamre AK Subscriber Subscriber

    Not much room to probe the phono board. I am away for a few days. When I get back I will get at it again. Having a real problem reading the schematic and understanding where to look.
  16. KutzlerTrans

    KutzlerTrans Jennie & I with Buddy and Barney. Subscriber

    If in doubt, swap the phono boards left/right output pins with the wires stil attached and see if the problem switches sides.
    Not easy to do if you cant get to them, but r401/r402 are your inputs.
    Swap the wires before the resistors to make sure its in the board or after.
    Your relay contacts are your outputs.
    If you can switch them before the relay, it would separate the relay from the list of suspects, until your sure its not in the board.
    If the relay is bad, the problem would remain on the same side.

    Look for loose pins and bad solder joints or cracked traces under the relay.
  17. Fhamre

    Fhamre AK Subscriber Subscriber

    Thank you for the advice. I will attempt to try swapping inputs r401,r402.Won't likely get to it for at least two days.
    May not be able to switch but I might be able to measure voltage on pins 2 and 5 to compare,if that would help. We shall see.
  18. Fhamre

    Fhamre AK Subscriber Subscriber

    The picture attached shows the 10 pin connector J410,there are no wires to swap.
    I did take a few measurements. I took one side off to get better access.
    Pin 8 on J401 -.009V when phono not selected on selector assembly PJ00,when selected drops to -.003v
    Pin 9 not engaged .04v,engaged .012v
    I also measured FETs Q401 G 0v,S 23.4v,D 23.6v,Q402 G 0v,S .181v,D 5.6v
    So big difference there. Can't tell which FET is getting the correct voltage. ?
  19. Fhamre

    Fhamre AK Subscriber Subscriber

    Any body out there have the original service manual or schematic?
    The pdf that is out there on the net is not clear enough to see all the voltages. That and I am schematically challenged.
  20. marantz1300dc

    marantz1300dc Marantz Remember Subscriber

    Pacific NorthWest
    Something like this? :) A little rusty on my scanning....I'll post what I can when I can. These are from my original 1300DC SM.

    Attached Files:

    Last edited: Apr 25, 2017

Share This Page