Marantz 510 - Rebuild?

[LHMAudio]

I have a Marantz 510 that still works, but has been sitting for many years (>10). Before powering it up I put in new used Filter caps, but other than that made no changes. I checked the DC offset and it is in the neighborhood of 0.050 VDC. It sounds OK with no distortion that I can hear.

Is it worth doing any work such as replacing capacitors? Or should I use the power supply and cooling tunnel for a new amp project?

Advice is appreciated.

Lindsay

[LHMAudio]

Some of the specifications are:

256 Watts per channel at THD 0.05% into 8 ohms
Slew rate of +-15 volts per micro second
Phase shift leading 9 degrees at 20 Hz and Lagging 10 degrees at 20kHz
Damping factor greater than 100 at 1 kHz into 8 ohms
Hum and Noise 110 dB below rated output into 8 ohms

The schematic lists four S41775 and four S41776 output devices per channel.

Lindsay

[anatech]

Hi Lindsay,
Replace the bypass caps on the amplifier driver boards now. Also the electrolytics on the same board. The feedback cap to ground is known to go open, cutting off bass response.

Check that the shoulder washers for the power transistors haven't melted. This will release the normal mounting pressure on the output transistors.

The thermal switches may have poor contact by now. Check, one pair is for the fan, the other is your speaker output.

Your DC offset is high for that model. Check the beta match on the diff. pairs and replace if they have drifted. Then adjust the DC offset.

If you do all these things your amp will sound much better. If you do not replace the bypass caps, your amp may overheat and fail.

-Chris

[LHMAudio]

Anatech,

Thanks for your quick reply. The power supply caps came out of the Haffler DH 500 I just upgraded and don't fit (too tall) so I will need to find replacements. Should I add bypass caps as well?

Thanks.

Lindsay

[anatech]

Hi Lindsay,
What do you intend to do with the amp when you are done? If you plan to use it, then buy good commercial grade caps for replacement. Look for high ripple current ratings. 105 ° performance is not required, 85 ° is just fine in this amp. You can bypass the caps. It won't hurt, but I don't have any idea if it will help. Each PCB has film bypass caps on it that you will replace as step #1.

Use the caps you have in there to work with until you decide if you are happy or not with the sound. That way you don't get into a big expense until you are sure. Keep in mind that these are interesting amps. The outputs are of a stacked design to get the voltage rating needed for the outputs.

If the amp were mine, I would take the heatsink assy. apart and clean it. Regrease and reassemble after you measure the outputs for leakage and gain match. They can degrade over time. Never assume anything. If you find bad outputs, replace them with MJ21196 and MJ21195. They should work okay. It goes without saying that these should be matched for beta. The service manual indicated matching for many of the transistors used in these models.

-Chris

[LHMAudio]

Chris,

Thanks for the reply. I don't have a specific use for the amp right now other than a back up for my Haffler DH 500. I may take this on as a long term project. I don't know how to match transistors so I will be doing research first.

Thanks for your help.

Lindsay

[anatech]

Hi Lindsay,
Okay, I was just trying to determine what direction you should take with it. May as well do a good job on it.

Look for something like a Heathkit IT-18. It will measure DC beta and I've found this model correlates well with real life. Match buy measuring the rough gains. The ones you figure are close, run through again by calibrating to one and just seeing where the others fall in relation to the cal mark.

Do not over tighten the power transistors. On Semi has some great mounting information in their app notes. If I figure out which one it is I may send it to you.

-Chris

[LHMAudio]

Chris,

Thanks for the recommendation on the Heathkit. It looks like they are available used online for around $30 so I'll see if I can pick one up. This should keep me busy for a few weekends. If I get some time I'll see if I can search the On Semi site for that app note. I'll post it if I find it.

Lindsay

[anatech]

Hi Lindsay,
I have 4 or 5 transistor testers, this is the one I use the most. I've also made an smt adapter socket and a Japanese pinout adapter. This one also works for TO-220 and TO-126 cases. You won't regret picking one up as long as it works. I have the manual if you need it.

-Chris