resistance check, terminal 1,2,4&5

[pro_crip]

I finished wiring up my crack today and did a quick resistance check. Everything was fine except for the aforementioned terminals. At 1&5 I got 23k, steady, which is the value of the the resistor between those terminals. At 2&4 I got 0.2, essentially zero which the manual warns against. I checked everything that goes to those terminals and everything was kosher. I resoldered all 4 terminals and rechecked resistance and got a repeat. At this point I started getting cross-eyed, reminding of my days of studying orgo, so I shut it down for the day. Would it be okay to do the voltage check with those numbers or should I straighten things out first? Anyhoo, it's time to veg out with the simpsons. Thanks.


Rich

[Jim R.]

How do the pins on the 9-pin socket look?  Any solder bridges there?

-- Jim

[Paul Birkeland]

At 1&5 I got 23k, steady, which is the value of the the resistor between those terminals. At 2&4 I got 0.2, essentially zero which the manual warns against.
Rich

If you are measuring from ground to 1 and 5 and you get 23k and 0 at 2 and 4, you have a short somewhere in the circuit, likely in the power supply.  I would check the wiring back by the transformer first, DO NOT turn the Crack on before you resolve this.

[pro_crip]

I forgot to mention that I'm installing grufti's psu tweak. Well I just spent the last coupla hours checking my wiring and comparing it to the manual, making sure of orientation of parts and whatnot and that's all kosher. I checked for solder bridges with a magnifying glass (my eyes are one of the few parts that work according to spec on my body) and that was fine. To double check to make sure none of my solder joints were cold I used the continuity function on my DVM and that turned up nothing as well. During this check I noticed there is continuity between power transformer terminals 6&7, which is connected to ptt 9&10. Is that supposed to be? A more thorough examination will come on tues., concentrating on the power supply.


Rich

[pro_crip]

Well, I've gone over the wiring with a fine tooth comb and a magnifying glass. No solder bridges and everything's where it's supposed to be. I just re-soldered all the joints, to make sure there were no cold joints and that didn't help. I'm gonna tear it down and rebuild it. I did something wrong somewhere, I just can't seem to find it.


Rich

[JC]

This is the point where I usually have a friend look over the work.  Even someone who doesn't do electronics can spot things that I have overlooked because I've stared at the thing too much.  And, usually the things they spot are "Duh!" simple, in my case.

Of course, you have verified that you have allowed for any manual corrections or updates.

[grufti]

Don't despair: checking to make sure that you have noticed and followed all manual corrections is definitely a good piece of advice in this case.

How about posting a couple of pictures of the belly of your beast?

I'll look at my power supply to remind myself what I did and how I installed the extra parts. I have never gone back. It still has the extra capacitor and works like a charm with the Speedball these days [by itself originally].

[pro_crip]

Grufti, your psu tweak was easy to install. I made sure all the striped ends and non-striped ends of the caps were all connected, just like in the manual. A complete tear down and rebuild is no big deal. Aside from dialysis I literally have nowhere to be or anything to do. So a couple of hours of desoldering today was right up my alley (though planting my butt in front of the tv for some college football would've been better in retrospect). I was in the middle of desoldering power transformer terminal 10 when Down popped on the radio and I got distracted by a riff for a sec., which is all it took for the metal tab to heat up too much and come out of the plastic base. In the process, a little wire running to the tab got disconnected. I managed to get the tab back in the base, resoldering that wire (which I assume carries the juice and therefore needs to be reconnected) will have to wait until tomorrow. I need to think about dinner. Oh yeah, I stupidly grabbed for the tab when I saw it pop free. My middle finger will curse me the rest of the day. Stupidity does get punished.

Rich

[pro_crip]

A complete tear down and rebuild yielded... the exact same problem. I made the same mistake twice? I don't understand why a resistance reading at terminals 1&5 would be fluctuating, they aren't directly attached to the filter caps. Shouldn't I be getting a 22.1k reading, which is what I get? According to the manual: A6, B1 and the 22.1k ohm are attached to terminal 1. The last filter cap is attached to B2&5, which in turn is connected to terminal 2, so I can understand that reading fluctuating. Instead I get 0.3. I used the continuity function on my DVM to check for cold joints and I got it from terminal 1&2 all the way to the power terminal. Just to be safe I re-did all those joints. I don't know what to check next. Thanks for any and all help.

[ironbut]

Hey Rich,
Is there a way you could post a picture of or two showing the the two tube sockets and another showing the octal and the power supply in medium close up shots?

[grufti]

I am finally back near my version of this amp. It is late now, but I'll respond to your questions to me tomorrow.

[pro_crip]

Sorry it took a few days, but I finally have some pics. Now that I have this whole macro mode thing figured out on my camera, I can take other pics if these aren't good enough. Sorry I can't figure out html code so I can't embed the pics, hope the links work.

9 Pin Socket http://www.flickr.com/photos/54358207@N04/5033567226

Octal Socket http://www.flickr.com/photos/54358207@N04/5032948041

Power Supply http://flic.kr/p/8EKb7v

If these angles aren't good enough, let me know and I'll take an appropriate pic.
Thanks
Rich

[ironbut]

It might just be the picture, but check to be sure there isn't a bridge between pins 2&3 on the 9 pin socket. Also, it may be out of picture but, there should be a grounding wire from terminal 3 to the pot.
It would probably be a good idea to take a picture of the other side of the terminal strip (1-5) and how it's connected to the 8 pin socket.
A clearer picture of the power supply (including the diodes) wouldn't be a bad idea either.

[pro_crip]

That wasn't a bridge, it was the tail end of the led. It was wrapped around A3 and the tail end looked like it was touching A2. I've since trimmed it flush. There is a wire connecting the ground of the stepped attenuator to T3, I ran it behind the terminal strip and it's lying flat on the chassis so it's hard to make out in the pic. I took some more pics, I tried to get as much of the power supply as possible but all the wiring connecting the +++ and the --- ends of the filter caps is tight up against the terminal strip and hidden by those big resistors and the filter caps themselves.

Photo 1 http://flic.kr/p/8EU8AL

Photo 2 http://flic.kr/p/8EQWRc

Photo 3 http://flic.kr/p/8EU8BW

Photo 4 http://flic.kr/p/8EU8BW

Photo 5 http://flic.kr/p/8EU8BW

Photo 6 http://flic.kr/p/8EU8BW

Photo 7 http://flic.kr/p/8EQWST

Thanks for looking.

Rich

[pro_crip]

Here are the pics of the back of the first terminal strip.

Photo 1 http://flic.kr/p/8FpgCm   In this one the red wire on the right runs to B1 and the one on the left runs to B2

Photo 2 http://flic.kr/p/8Fm6jZ  In this one the red wire on the right connects to T2 and the white wire runs to B4

Thanks for looking.

Rich