Better Late than never; voltage problems...

[marantzfan]

Last year when BH was doing a cyber Monday sale, I bought the Seduction with Upgrade kit and shortly after if got here I got it put together (except for the upgrade isn't installed yet).  I stopped at that point because my voltage readings were off and then a gnat flew by and here we are nearly a year later. 

So, hopefully someone here can help me to figure out what I have wrong here so that I can get this phono pre singing along with my Stereomour.

Here area list of the resistances that are not within tolerance:

Terminal    Resistance    My Resistance
1                  *                4.1
2                  *                4.1
6                  *                3.5
9                  *                2.3
12                *                330
15                *                330
17              165-200          4.3k
19              175-210          4.3k
22              165-200          0
24              175-210          10
25                *                330
27                *                17

Couldn't get a reading at A3, B3, A8, B8


Here are a list of the voltages that are not within tolerance:

Terminal      Voltage      My Voltage
6                  6.5VDC        1.7VDC
9                  6.0VDC        1.3VDC
27,37            70VDC        134.4VDC, 134.4VDC
29,39            70VDC        132.0VDC, 132.0VDC
30,40            70VDC        131.0VDC, 131.0VDC
A1, B1            70VDC        130.0VDC, 130.0VDC
A3, B3          1.6VDC        168mv, 177mv

Also, the transformer seems to get very warm.  I didn't leave it powered up for very long, just long enough to get the voltage measurements.

I've visually checked and double checked my work and can't find anything suspicious.  Any help would be greatly appreciated.

Anthony

 

[Paul Birkeland]

Hello Anthony,

We are certainly still quite up for helping you with your Seduction!

There is a small cluster of 1N5818 didoes with a 1.2 Ohm resistor and a 10,000uF cap.  I believe you have a backwards diode there, as you're not getting anywhere near 6.3V.  This would also explain the hot power transformer.  It's also possible that the 10,000uF cap is in backwards, which would cause similar issues.

Once you get 6/9 to read around 6V, you'll get more reliable voltage readings elsewhere.

-PB

 

[marantzfan]

Here is the diodes section.

 

[Paul Birkeland]

Hmm, nothing wrong there.

How about pins 4/5 on each 9 pin socket? 

Also, you can pull the tubes and repeat the voltage checks for the ~6V terminals, it should creep up a bit over what's specified.

I also see that you have 0 Ohms at terminal 22, can you double check that?  There is symmetry back there on those two strips, so 0 Ohms at 22 should indicate 0 Ohms at 17, but both of those are a mistake.  The bare buss wire should only touch terminal 16, maybe there's a short between 16 and 17? 

 

[marantzfan]

Blown fuse.  I see a trip to radio shack in my immediate future.  These are fast blo fuses right?

 

[Paul Birkeland]

Slow blow 0.5A or fast blow 1A will work.

A blown fuse indicates a short (as we were discussing), a miswire, a backwards cap, or a backwards diode. 

-PB

 

[marantzfan]

Installed new 1am fast blow fuse and it shorts instantly at power up....  Hmm

 

[Doc B]

Try disconnecting the power transformer leads that connect to the DC heater supply and fire it up again. If a fuse holds you know the short is in the heater circuit somewhere.

 

[marantzfan]

Just to make sure I understand this correctly, should I disconnect the two transformer wires coming into terminals 1 and 2 then power up to see if the fuse holds?

 

[Grainger49]

Yes, that is what they are saying.  And tape the wires just to be safe.

 

[marantzfan]

Ok, disconnected  transformer leads from terminals 1 and 2 and taped each to be sure.  Powered up and fuse blew instantly but also, cap between terminals 20 and 25  is bulging.  I verified that it is oriented correctly as well as the diodes underneath it..??

Bad transformer?

 

[Grainger49]

When they swell they are bad, probably open, but maybe shorted.  I posted a picture of one that came out of my air conditioner compressor a year ago.  The top was spherical.

The conclusion would be that the leads to T1 and T2 are ok, the high voltage supply is the problem.  Is that where the cap on T20 to T25 is?

Transformers are not often bad out of the box.  But if molested they can give up smoke.  You usually see smoke from them.  The fuse is there to save the transformer because it is the single most expensive component.

 

[marantzfan]

Haven't seen any smoke yet...  I'm completely dumbfounded on this one.  Btw, I just noticed that the resistor under that cap looks like some of the ceramic coating got cooked off of it...?

I've been sooooo happy with my stereomour I just want to get this pre working so I can listen to records again. 

 

[Grainger49]

I looked at my schematic.  T20 to T25 is the first high voltage capacitor.  There is no resistor from those two terminals but there is one from T25 to T15 (1k Ohm) and one from T15 to T14 (270k Ohm).  Which one is burned?

 

[marantzfan]

Actually the resistor looks chipped not burnt; maybe I did that installing it.  It's on the corner of the resistor.  Also, the resistor doesn't connect to the burnt cap but the terminal next to it...

I'll snap a few pictures of this area when I get a chance.

 

[Paul Birkeland]

Powered up and fuse blew instantly but also, cap between terminals 20 and 25  is bulging.  I verified that it is oriented correctly as well as the diodes underneath it..??

Bad transformer?

Either the diodes are in backwards, the cap is in backwards, the 3 high voltage transformer wires are not properly connected, or some other issue is present. 

I now would suspect that your low heater voltage is due to a miswire in the high voltage section dragging everything else down. 

 

[marantzfan]

I have already verified that the diodes and caps are properly oriented so the only thing left is the wiring.  I'll take a look at the wiring and compare it to the instructions.  I hope this didn't cause any damage to the transformer.

Also, I wonder if I can get a replacement cap locally somewhere...

 

[marantzfan]

I'll have to remember where to look for the wiring as the manual I have desciribes three different colored wires coming off the transformer but the kit I have has no wires coming from the transformer and was all connected with plain black hookup wire.  I seem to remember that there was a link somewhere to an update but its been a while.  :-\

 

[Paul Birkeland]

The middle black wire needs to attach to the ground buss, and the outer two need to feed the first 0.01uF/1.6KV cap.

 

[marantzfan]

I'm at work right now and my instructions are at home.  Can you do me a favor and remind me the size of the capacitor that is cooked so that I can see if I can get one at radio shack on the way home from work today.  If I can, I can replace it and fix the wiring (if miswired) so that we can see where we are at tonight.