Eros resistance troubleshooting

[grosen]

I think I've got two unrelated problems, and I bet there's no solution short of checking every connection one more time, but I thought I would run the symptoms by you just in case. 

Problem 1.  The resistances at the terminals at the terminals are almost all systematically high by exactly 15k ohms. The terminals that should be grounded (0 ohms) are all fine.  The problem cases are:

Terminal:    Should be:  Measured value:
2                71k               85k
4                60k               75k
9                39k               46k
10               39k              46k
12               60k              75k
14               71k               85k

c1                39k             46k
c2                60k             75k
c6                39k             46k
c7                60k             75k

Problem 2:  A4, B4 and C4, which should all be infinite, all measure exactly 619 ohms.  I can't find a short anywhere.  I know the shunt capacotirs running from c4 and c5 to ground and between c4 and c5 are all ok.  So I'm stumped.  As always, thanks for your help with this.

[Grainger49]

Sorry nobody has jumped in.  I'm pretty busy but it will be over this weekend.

I'm with you.  The error seems to be reliably a given resistance.  

What does the meter read when you touch the leads together?  (on the scale you would measure 60k ohms)  What meter are you using?  Is the battery fresh?

Can you check a known resistor, out of the circuit in the 30-100k ohm range?

A4, B4 and C4 are all heater leads.  One heater lead should be grounded, the other should have the 10uF, mustard colored, Tantalum capacitor between it and ground.  I'm not naming leads as they can too easily be swapped.  

So it sounds like that capacitor is missing.  Take a look at the picture of the finished power supply board on page 17 of the manual, bottom of the page.  Nestled between the heat sink fins all the way to the right are the two Tantalum caps.  If one is missing, put it in.  If both are there rewet the solder pads and remeasure the resistance.  

[grosen]

Thanks for the quick response.  The tantalum capacitors were both in place and wetting the joints didn't help.  I pulled one to see if it might be open and managed to snap a lead in the process.  But it's out now and the problem remains. (This was the cap closest to the front of the preamp.)  I'll order a replacement and see if that helps.  Do you happen to know the exact specs of the capacitor?

As for the resistances at the terminals: the meter is an old radioshack meter and it's definitely working. Some of the resistances are fine, like the 47k and 470k's across the inputs and outputs.  The problem is in the RIAA network somewhere, so I'm still stumped.

 

[grosen]

Looks like I'm not the first to have these issues:

http://www.bottlehead.com/smf/index.php/topic,1322.0.html
http://www.bottlehead.com/smf/index.php/topic,2798.0.html

I thought I had checked the forum, but I didn't see these until just now.  From PJ's last comment on the first thread, it sounds like the readings at B4 and C4 are ok, that the * in the manual is an error, and that my high resistance readings are ok.   Is that right? If so, I'll just replace the capacitor I snapped off and fire it up.

[grosen]

Success.  I decided to call the resistance readings ok, checked the voltages and plunked it into the system.  Sounds terrific so far. Dead quiet.  A lot more gain than the Seduction, and noticeably more detail.

Thanks as always for the help.