Marantz 500 repair/ rebuild Help!!!

Love Vintage

Active Member
I have a Marantz 500 amp that I have had for a couple of years and decided to look at it. I plugged it into a dim bulb tester and it glows bright, so I hooked it up my variac and slowly raised the voltage, when I get to about 100v 4 resistors started smoking so I shut it off. The resistors are on the power amp boards 2 on each board, on the A2 board they are R204 & R210.

I then removed the 4 fuses from the back panel, removed the driver boards and disconnected the power to the power amp boards with the connectors on the bottom. Brought it back up on the variac to 120v it was drawing about .75A, after a few seconds all 3 relays clicked. I measured the voltage at the rectifier/relay board and the voltage is supposed to be +&- 91 and measured 86.7, the other voltages should be +&- 82 and they measure 78.5.

So don’t know what to do next, my first instinct is to plug the connectors back in to the power amp boards and try it again, but wanted to ask the experts opinions.
Thanks
Terry
 
I would pull the outputs and test them first along with the driver transistors. If you find one shorted, which you lost likely will, replace all 10 of them (5 pairs).

While you're in there I would clean the contacts on those exposed relays.
 
I would pull the outputs and test them first along with the driver transistors. If you find one shorted, which you lost likely will, replace all 10 of them (5 pairs).

While you're in there I would clean the contacts on those exposed relays.
Great I will do that tomorrow....
 
I would pull the outputs and test them first along with the driver transistors. If you find one shorted, which you lost likely will, replace all 10 of them (5 pairs).

While you're in there I would clean the contacts on those exposed relays.
Ok I had some time today and was able to remove and test every semiconductor on the power amp boards and heat sinks also on the driver boards.

All the outputs, drivers and pre drivers tested good, the only shorted transistor on one power amp board was Q202, I also replaced R210 & R204 on both power amp boards, because they were all burned.
The power amp boards also had trimmers of different values (Helitrim 78PR1K & 78PR2K) soldered where R202 goes.

The driver boards had no bad transistors, just R151 & R156 burned on both boards, so they were replaced also.

I’m not sure what to do next, should I put it back together and try it or test all the resistors and capacitors next?
Any help would be greatly appreciated.
 
Today I tested all of the caps on the driver boards and replaced the same cap on each board. I will test the caps on the power amp boards tomorrow and do a quick check of all the resistors on all 4 boards, until I get some direction I will keep testing.
Thanks
Terry
 
Have to you tested the zener on the base of Q202? Its CR201.

After replacing Q202, still failing the dim bulb?

Anytime you find burnt up resistors, it's the effect of an over current condition. Most if the times this is caused by a shorted semiconductor. Just replacing the resistors without determining the cause will lead to failure again.

These are good clues though. Seems you've taken care of the issue, hopefully on the 200 card. I would be hunting down the cause of R151 and R156 burning up.

Making progress! Baby steps..
 
Last edited:
Have to you tested the zener on the base of Q202? Its CR201.

After replacing Q202, still failing the dim bulb?

Anytime you find burnt up resistors, it's the effect of an over current condition. Most if the times this is caused by a shorted semiconductor. Just replacing the resistors without determining the cause will lead to failure again.

These are good clues though. Seems you've taken care of the issue, hopefully on the 200 card. I would be hunting down the cause of R151 and R156 burning up.

Making progress! Baby steps..
Yes I tested the Zeners, all 4 tested good I have not put it back together and put it on the dim bulb.
Thanks
Terry
 
I found an open capacitor on the power amp board C202 I think, I also found a lot of resistors out of spec I can replace the 1/2 watt ones but don’t have the 1, 2 & 5 watt. I will continue to check things out.
 
I’m enjoying following this thread. Don’t be discouraged if not many people chime in. Most have never seen a 500, much less rebuilt one. Kudos for jumping into it. Keep us posted. :thumbsup:
 
I’m enjoying following this thread. Don’t be discouraged if not many people chime in. Most have never seen a 500, much less rebuilt one. Kudos for jumping into it. Keep us posted. :thumbsup:
Thanks for the encouragement, I will keep at it just decided to check everything as I go. The driver boards are connected with the small pc board pins like the 3600, 3800, 3250B etc. I’m trying to figure out a way to clean them and where they plug into, so far I have used fine steel wool and Deoxit on the pins and sprayed it into the holes then plugged them in and out several times. If someone has found a better way of clearing them let me know. I will try to add some pictures today.
 
Here are a few pictures of it torn apart..... hope I can get it back together.
 

Attachments

  • 604BCC9D-B02B-4246-8A4F-277A1646E693.jpeg
    604BCC9D-B02B-4246-8A4F-277A1646E693.jpeg
    63 KB · Views: 52
  • DBD5F912-C605-44BA-A085-2276B50AFFA2.jpeg
    DBD5F912-C605-44BA-A085-2276B50AFFA2.jpeg
    79.7 KB · Views: 51
  • 998EB0E4-4212-4014-9243-0ABC5DD65C1F.jpeg
    998EB0E4-4212-4014-9243-0ABC5DD65C1F.jpeg
    75.7 KB · Views: 49
  • BCCE3A0C-C884-42B8-B6DE-85B6966D563A.jpeg
    BCCE3A0C-C884-42B8-B6DE-85B6966D563A.jpeg
    81 KB · Views: 49
So I put it back together yesterday and it passed the dim bulb test without the driver boards installed, then I installed the driver boards one at a time after hooking it up to a variac. The first board was ok, current increased a little but when I installed the second board the current increased from .75A to about 2.5A then the 2 fuses for that channel popped.

I guess I will take it apart and test things again, I will order resistors and replace all that are out of spec first.

I will also test the semiconductors again on my DCA75, if the test ok should I trust that, I have read that the hfe can be to low, how do I find specs on that?
 
Owned , repaired and hopped up several 500s. There nothing like one that is in top shape...and I have model 9s to compare to....

But they are very complex and need a lot of attention...

Love my main system with the 500 and Fs, blows me and every one that hears it away...

Incredibly detailed and powerful ... I tell people that it is a “tornado” of sound but is very very detailed and controlled....

Search for post by me and 500... you will find a lot...

Power and grounding is critical for it... I run my on 240v which is an undocumented config that works great.

Johnk
 
Owned , repaired and hopped up several 500s. There nothing like one that is in top shape...and I have model 9s to compare to....

But they are very complex and need a lot of attention...

Love my main system with the 500 and Fs, blows me and every one that hears it away...

Incredibly detailed and powerful ... I tell people that it is a “tornado” of sound but is very very detailed and controlled....

Search for post by me and 500... you will find a lot...

Power and grounding is critical for it... I run my on 240v which is an undocumented config that works great.

Johnk
I have looked at all of your posts, I will be looking for semiconductor substitutes soon as I go through the boards again, I might need some help with that if you are open to it. Thanks for responding,
Terry
 
So I ordered replacement parts and will go through each board and replace the out of spec parts. I think I will start with the power amp boards and go from there.

I have read about others keeping the main filter caps after testing, is this an ok idea? What is a good ESR on a 21,000 uf cap?
 
300$ for a set of main filters.... at some point it’s time to replace them.

Your not going to accurately measure the esr.....
 
Value range is extremely low for that size cap.... How low will your ESR meter go?
 
Not low enough.... you need .000 .... 3 digits past the decimal point.

Try it and see what they read.... But don't forget there are two of them in parallel....
 
Back
Top Bottom