Restoring a Marantz 6300 TT

[LuisNiels]

hello everyone, recently i managed to find this 6300 for 25 dollars
obiously it was (and still is) in very bad shape, but for the price i
couldn't go wrong, so as you might imagine it came with some issues.

cosmeticaly: needs alot of work, needs re-veneering,
new paint for the platter, needs 4 new feet, needs front emblem, needs
the tonearm counter weight, 2 small rods for the antiskating.

functionality: it came with the motor completely seized, it took some force
to free up the rotor, once out it was a matter of cleaning the shaft and sleve
from old grease and apply new lub.. so that's fixed, but now the motor
doesn't keep constant RPM, so i started checking voltages and found out that
all check points from the service manual were low except for J811 witch was to
high, sould be 0.6V and it was 7.6V, behind J811 is R809 so i check that and it
was out of value, shoud be 15K and it was only 10K.

my question:
i also disconented J801 and J802 (see schematic) to check the transformer output
and it only puts out 30V AC and right next to the rectifier is the first checkpoint
witch has to be 35.2V... my question is, do you think the transformer might be bad??
i can't find anywhere what's the nominal output voltage for this transformer


i'm going to do a complete power supply rebuild, recap, resistor etc. but i need
to know whats up with this transformer... i hope someone came across with this
issues and can give me a little help, would be much appreciated!

 

[catrafter]

I assume you have it set to 'Auto' and 'On'.
Let me say I have never worked on a Marantz turntable. C003 could be defective, but I suspect the problem is that the photo transistor portion of optical coupler H002 is bad or there is something blocking the light from reaching it.
I don't have a source for the optical coupler.

Tom

 

[Echoplex]

Going by your measurements, the transformer voltages you're getting are correct; primary side should be 120Vac, while the secondary side should be 30Vac.

However, the voltages for transistor H803 on the power supply are low everywhere, and they should agree with the schematic:

• 34V collector
• 17.7V base
• 17V emitter

Have you pulled R809 resistor out of circuit and tested it? I would recommend just to rule it out.

Also, I agree with catrafter, your phototransistor PH10A will need to be replaced, and it wouldn't hurt to replace the tantalum cap C003 as well.

I use these for the phototransistor replacements:
Optek OP535B - Photodarlington
Mouser part # 828-OP535B

 

[LuisNiels]

Thank you very much @catrafter and @Echoplex... i will check C003 and H002, replace H803 and phototransistor PH10A

 

[einstein812]

Going by your measurements, the transformer voltages you're getting are correct; primary side should be 120Vac, while the secondary side should be 30Vac.

However, the voltages for transistor H803 on the power supply are low everywhere, and they should agree with the schematic:

• 34V collector
• 17.7V base
• 17V emitter

Have you pulled R809 resistor out of circuit and tested it? I would recommend just to rule it out.

Also, I agree with catrafter, your phototransistor PH10A will need to be replaced, and it wouldn't hurt to replace the tantalum cap C003 as well.

I use these for the phototransistor replacements:
Optek OP535B - Photodarlington
Mouser part # 828-OP535B

Thanks for your guidance on this. I ordered the phototransistor above and soldered it in and the auto shut-off still wouldn't trip when the blade broke the light, so I replaced the LED with a real bright new one and still wouldn't trip it. I jumped the posts and it trips the auto shut-off so I know it must be the phototransistor. So then I reversed the phototransistor in case I soldered it in backwards but still did not work. Any ideas what else I can try? Thanks in advance. Dave.

 

[Echoplex]

Check all voltages at the locations listed on the schematic for the auto-mode circuit first. And, check with the auto mode on, and retest with it off to compare.
There's quite a few components involved in the auto-mode circuit and it can be tricky trying to find the culprit, but start there and see what you get.

 

[einstein812]

Check all voltages at the locations listed on the schematic for the auto-mode circuit first. And, check with the auto mode on, and retest with it off to compare.
There's quite a few components involved in the auto-mode circuit and it can be tricky trying to find the culprit, but start there and see what you get.

Thanks...I'll check the voltages and see if I find anything off.

 

[Novice44]

I don't believe your resistor values are bad, I think you have a newer version of the power supply than reflected on the schematic, along with a C806 capacitor. If the arm Cue Up button works in manual, then the problem is somewhere in the LED and phototransistor circuit.