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Marantz Model 18

tonebells

tonebells

AK Subscriber
Subscriber
I picked up an 18 (18-3012) from @nolasally and it needs some work.

What I know so far
  • Scope is dead
    • Voltages to the scope board are good
    • One of the fets Q1201/4 had been replaced with a depletion mode mosfet.
    • Scope driver board done. Found bad vertical trim pot. Scope is now working. (08/06/2017)
  • FM dead
    • All tuner boards have good voltage to board
    • See post 15 (07/09/2017)
    • I see tuner signal at 5B on the MPX Oscillator board. I tracked the signal to the gate on Q510. (07/17/2017)
    • I have very low sound on FM (07/18/2017)
    • Swapped limiter. Better volume still distorted (07/23/2017)
    • Swapped MPX boards tuner mostly working (07/25/2017)
    • FM stereo is distorted in right channel. (08/06/2017)
    • Installed trimmer R328 FM muting now works. Picture add post #85 (08/10/2017)
    • Swapped Q605 and Q606 the issue moved to the left channel. I need a sub for 34-1012. (08/21/2017)
    • Replaced Q605/Q606 with new 2N5460s and FM sound good. (08/26/217)
  • Right channel only work in left + right or with high blend engaged
    • Cleaned all switches and jack and all is well with the right channel.
  • DC balance trimmers will not move. (08/06/2017)
    • Dismantled R1016s cleaned they should now work. (06/05/2021)
  • Bias will not come up to .08 volts. (08/06/2017)
    • I have learned a lot since I put this one on the shelf. The amps have a lot of iffy repairs that will need to be reworked. (06/05/2021)
    • See post 97

  • Replaced speaker relays. (02/21/2022)
Bias will not come up to .08 volts. (08/06/2017)
Does anyone have a recommendation on a sub for the fet. I have seen 2N5116 or 2N5114 use here. I see where people have used TIP47, 2SC2611, 2SC2371 or KSC3503 for Q1202/3/5/6. If someone has experience with one of these your input would be great.

IMG_3975.JPG
 
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I replaced the 4 scope transistors along the bottom heat sync with TIP47 a year and half ago. The pinout is different so they don't plug into the board. No problems with the scope since. Also look for cold solder joints on the scope board.

IMG_1683.jpg
 
Download the service manual on HiFi engine. There were some service bulletins for the tuner. May not address or your issue though...
 
I use 2SC2611 for the scope, work fine.
Simply need to be installed under the heatsink:

a871eb18-8464-4f75-96f0-03a2ad32a95a.jpg
 
Thanks for the replies and pictures. I will try some of the TIP47 and 2N5116 and see what happens.
 
I guess I will need to get out my scope to look at the tuner. I assume I should start at the point the signal leaves the front end. The question is what setting should I start with on the scope. I have an RF signal generator to send a known frequency to the input.

Thanks

Tony
 
IMG_4006.JPG
IMG_4008.JPG
This may have something to do with the scope not working. It is very rusted.

Add 08/01/2017
IMG_4085.JPG
 
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txturbo said:
Maybe it was sprayed down with a cleaning agent that was not correct?
Click to expand...

Hard to say. The good news is some D5 and heat and it is free and working. Now how far do I go in cleaning it up. I have been know to break things trying to make them look good.

Tony
 
tonebells said:
Hard to say. The good news is some D5 and heat and it is free and working. Now how far do I go in cleaning it up. I have been know to break things trying to make them look good.

Tony
Click to expand...

If the wipers are now working can you test the pot via a meter? I wouldn't make that switch perfect if you think it will destruct. Just get it working and exclude it as the problem. You can always get another pot from a donor parts unit or Mouser later.
 
monkboughtlunch said:
If the wipers are now working can you test the pot via a meter? I wouldn't make that switch perfect if you think it will destruct. Just get it working and exclude it as the problem. You can always get another pot from a donor parts unit or Mouser later.
Click to expand...

It tested fine. So should be good to go when I get the transistors.
 
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Try removing the signals that drive the scope board. If the FET's are shorted or other components damaged it may mess with the tuner. Possible but low. They should be 12E and 12C on the scope board.

On the MPX board what are the supply voltages?

+200
-36
-12
+12

Is the neon tube lit in the left corner?
 
Oh.... be super careful when working on the scope board. The high V can be stored in the cap for a while... learned the hard way :eek:
 
txturbo said:
Try removing the signals that drive the scope board. If the FET's are shorted or other components damaged it may mess with the tuner. Possible but low. They should be 12E and 12C on the scope board.

On the MPX board what are the supply voltages?

+200
-36
-12
+12

Is the neon tube lit in the left corner?
Click to expand...

Voltages in are good.

C/E are unhooked. Fet Q1201 on the scope board was bad so Q1201/1204 are not installed at this time.
 
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