Marantz Model 18

Is UF4006 to good replace CR5 in the scope HV power supply and CR1201,CR1202 and CR1203 on the scope driver board?

Tony
 
I just found time to get into the scope power supply to do the cap and diode. Testing the old one shows forward voltage of 3.39v (I think it has been replace before) The new UF4006 is .56v. Is the UF4006 a good replacement?

Tony
 
I installed the UF4006 and it seems OK. The scope driver board is still not right with new fets and transistors. I have no 105volts on collector of Q1202.

Tony
 
A quick look at the amp has uncovered the DC balance trimmers will not move and bias will not come up to .08 volts.

Tony
 
Is the FM distorted or the AMP?

Did you check the emitter resistors?

Are both left and right having a problem?
 
Do you have a detector assembly from the donor receiver? If so try swapping it and see if the distortion changes. It could be that the detector is out of alignment. Not sure if you have the service bulitens so I attached the two that may help.

Warning..... Be very careful adjusting the coils on the MPX board. The little plastic adjuster that has a screw driver slot in it can shear right off of the coil core. I found out the hard way....



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I have all the tuner parts. I will see what happens. The more I look at this unit the more I find that has been replace in past service. I have found that the transformer was even replaced.

Tony
 
I have all of my notes from the 18 at work. I will check in the morning and see if there is anything I can find.
 
I have seen this issue as well on one of my 18's. It was also missing a wire if I remember to the MPX board and maybe the muting switch? I'll see if I can take a picture of it.

Does your parts unit have the mute pot?
 
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