Custom Electra VI Wiring

[dcgillespie]

OK you Fisher console owners and gurus, if anyone of you have a good pic of the underside of the tuner/preamp chassis for this console, I'd appreciate your posting it in response.

At question are the connections to two of the cap terminals in the three section can cap. In my unit (with original can cap still installed as wired by Fisher), the connections to the 20uF/300 volt and 40uF/350 volt sections of this cap are reversed, based on the schematic, and the information stamped on the side of the can.

The Fisher schematic for this unit would certainly appearing to be drawn correctly, and accurately represent proper circuit design regarding the these caps in the circuit. So if that's true, then it means that likely only one of two possibilities exist:

1. The can terminals were in fact wired backwards by Fisher, or

2. The information stamped on the side of the can cap is wrong.

Any help is greatly appreciated, as always!

Dave

 

[larryderouin]

Dave; I've got a VII. The tuner /preamp are predominatly the same from the IV thru the vii with minor differences in the molex connectors and tubes IIRC. According to the schematic they look the same in the POWER SECTION. That's C74 A, B, C.

I talked with Tom a Hayseed Hamfest last year and we came to the conclusion that FISHER tagged the sections backward from normal convention in a lot of the units. Mainly the 400, 500C and 800C, TA-600 we were concerned with . They, numbered them in a counterclockwise rotation rather than follow the industry standard of clockwise. The symbology is correct, but they put in the sections on the bottom in a counterclockwise rotation. I've seen about 80% of the one's I've worked on that way. That would account for the "miswiring".
I'd go with #2.


I just did (Monday) a Tuner preamp/hybrid amp on a VIII(49A/49T) and the numbering went counterclockwise on the 3 section (tuner) and the 4 section(amp). The sections vs. the symbols were correct, but they were in a counterclockwise rotation rather than clockwise. Maybe one or a couple of the "Dutchmen" were LEFTIES!!!

Larry

 

[dcgillespie]

Hi Larry -- Thanks for your input, but I think I'm still confused -- first of all because I've never been aware of any clockwise or counter clockwise direction associated with can caps. I've just always matched a given terminal's symbol with the information printed on the side of the can, without any awareness of direction of terminal flow.

I guess I find it kind of hard that a manufacturer of can caps would knowingly let their product go out with the capacitance of a given terminal on their product not being what it is represented to be, according to the data they stamped into their can used with their product -- and then, for the manufacturer of the product using that mislabeled can cap to actively alter their build plans to accommodate the mislabeled product from the can cap manufacturer. It just sounds like a stretch.

In particular, C74A is shown on the schematic as a 20 uF cap. No voltage rating is given for this cap in the service manual -- although on the can itself, the 20 uF section is given as a 300 volt cap, which is an entirely appropriate voltage rating for the position on the schematic where the 20uF cap is located.

74B is given on the schematic as a 40 uF cap, with the can itself indicating that this section is rated at 350 volts -- and again, is an entirely appropriate voltage rating for the position on the schematic where the 40 uF cap is located.

The problem is, based on information on the cap itself, the wiring to these to terminals is reversed. The biggest issue this causes -- if the can cap information is accurate -- is that the 300 volt 20 uF section now has 275 volts impressed upon it, while the 350 volt 40 uF section only has 235 volts impressed upon it, which of course is completely reversed from a standpoint of safety reserve with regards to voltage rating. Also, from a circuit function standpoint, C74A need only be about 20 uF as indicated, while C74B needs to be every bit of 40 uF.

So you are saying that the unit is wired correctly, and that the circuit points are really in fact being serviced by the correct caps within the can because the can itself is mislabeled???

I guess if find it easier to believe that the can is labeled correctly, and that somebody at FRC blew the build instructions -- but let it go (if they even ever discovered it), because it does still work "OK" if the wiring is in fact reversed.

I'm not sure how the clockwise/counter clockwise thing works, as I don't know what the starting point for reference is. In any event, the middle terminal on my can is wired as C74B, but the can indicates that this is the 20uF/300 volt cap that should be wired to the C74A location. Finally, with the 20uF/300 volt section being the indicated value of the middle terminal, it stays in the middle of the three terminals whether you count clockwise or counter clockwise, so I don't see how direction affects this -- but I'm sure there's something I'm just not getting here. It just seems to me that there is more chance that the build is wrong, rather than the can being wrong -- but then of course, I could be wrong!

Thoughts?

Dave

 

[larryderouin]

I was taught (long time ago) to follow the shapes. Top to bottom 1/2 moon , SQ, Cir, Line or blank. And usually clockwise.

On this 49T (Hybrid 1965 version with 4 section cap C74) for example the sections are top to bottom 60uf/200V, 60uf/200V, 40uf 350V, 20uf 300V. 1/2moon, Square , Triangle, Line. And they go clockwise. Although the 1st and 2nd 49T's I did had can's that the shapes went in a counter clockwise rotation on the bottom. Boy THAT was a corker. Screwed me up for a week.

Now the manual shows them switched around in the parts list. A,B,C,D, 60/200, 60/200. 20/300, 40/350. They swapped 3 and 4. I'm presuming A=1/2moon, B=Sq., C=Cir., D=Line or Blank. But the cap side doesn't show it that way. With the 400 and 800-C a few people got bit by this and miswired, blowing a section as Tom built them according to the shape / specs that he was given. Some from the side of the cap and some from the manual. I've seen this on the 800C and 400 caps. The way the sections are listed on the caps don't match the parts list. Hence the confusion. We discussed it and he decided that he'd have all customers list what was actually on the old cap top to bottom and with the shape. He's building a database for the caps per model so eventually someone can call and say I have so and so model, and he can look them up and build them correctly.

It could very well be a case of both. According to Tom the shape convention for caps is top to bottom, 1/2 moon , square, triangle, either blank or a line. That is supposed to conform to sections A,B,C,D. But somewhere down the line it looks like someone @ FISHER apparently got confused with the values and the voltages. My understanding is the voltages go low to high A to D. And the values can be anything as long as the values line up.

Probably the best thing to do is to disconnect the sections and then test them with a cap checker to verify the actual vs. claimed value. Couldn't hurt. And you'd know for sure.

Larry

 

[dcgillespie]

All very interesting and informative stuff, Larry -- thank-you!

My three terminal cap is labeled half moon/square/triangle top to bottom just as you say (nothing in the blank spot), and has these arranged in a clockwise fashion starting from the half moon position -- but, it has the individual caps arranged with the highest voltage rated cap on top, progressing to the lowest voltage rated cap on the bottom -- which is how I have always seen caps arranged in their listing on the side of a given can. Therefore, the can itself would appear to follow standard protocol for can cap construction with regards to the order and direction of symbol sequence at the terminals, and for how the individual sections are listed on the side of the can.

If you accept that Fisher's intention then was to designate the same standard order of half moon/square/triangle relative to their schematic labels of sections A, B, & C as well, then it means that while the Fisher schematic shows the correct uF value at each cap location, their schematic designation of which cap is section A and which is section B in the can are reversed -- both on the schematic, and in the parts list.
Most importantly however, the actual unit is wired based on how FISHER shows the A and B designators on the schematic -- not how the capacitance values are shown.

Since those section A, B, and C schematic designators are a product of Fisher and not the manufacturer of the can cap, I am strongly inclined to believe that the error is on the part of Fisher, with the schematic/parts list designator error flowing right on down through to the assembly line build instructions, so that the finished products in fact ended up with the wiring for these two terminals reversed.

The bottom line is that there appears to be complete consistency in how the can cap itself was constructed, and there also appears to be an intended consistency in how Fisher translated can cap terminal designators into their section A, B, & C schematic designators, but in this case, something was lost in the translation process when the final schematics were drawn. It would appear to me in trying to unscramble the ambiguity, that it's another case where Occam's Razor applies.

Dave

 

[dcgillespie]

OK, since I know you've all been on the edge of your seat regarding the discrepancy of this project, I thought I'd give you an update. Here is what I know with a very high degree of certainty:

1. Four section size can caps in fact have their symbols labeled top to bottom on the side of the can as Half Moon, Square, Triangle, Blank, in that order. This is common to all major can cap manufacturers of the period. Sometimes the Triangle is a circle, but that's about the only variation between manufacturers.

2. The internal caps are arranged such that the top (half moon) terminal has the highest voltage cap connected to it, if the voltage rating of the internal caps varies from one section to the next. The remainder of the caps fall in line below the highest voltage cap, arranged in a descending voltage rating order. Therefore, the Square will be the next highest voltage rated cap section, then the Triangle, and lastly the Blank.

3. Now, when it comes to Fisher, there appears to be SOME consistent relationship between their section indications of A, B, C, and D and that of the can's symbols -- BUT THAT RELATIONSHIP VARIES BETWEEN DIFFERENT PRODUCT LINES. For example, with MOST of their integrated amplifiers, the sections A, B, C, and D tend to match up with the Half Moon, Square, Triangle, and so on respectively, so that the highest voltage rated section is in fact labeled as section A. However, in console FM Stereo Multiplex tuner/preamps, section A seems to always be identified with the lowest voltage rated cap within a circuit section (tuner or preamp), with sections B and higher representing increasingly higher voltage rated can sections, and therefore having the exact opposite relationship to the can's symbols from that used with integrated amplifiers. Receivers seem to be labeled like tuner/preamps, with section A being identified as the lowest voltage rated section, and proceeding up from there, with the highest voltage rated section being section D. It's as if there were two different drafting departments working on Fisher schematics, and one did it one way, and one did it the other.

So pity the poor engineers laying these circuits out for the production team. How the heck were they supposed to know that one did it one way, and one did it the other?

Clearly, they were unaware of the discrepancy, as MY UNIT IS IN FACT WIRED BACKWARDS. By measurement, the section that is supposed to be 40uF @ 350 volts is connected in the circuit where the 20 uF @300 volt section is supposed to be, and the 20 uF @ 300 volt section is connected where the 40 uF @ 350v section is supposed to be. Therefore, the can itself is correct in all aspects of its labeling and construction. And the schematic is also correct in terms of identifying what capacitance value is supposed to appear at the various places on the schematic. BUT, the inconsistent labeling of sections A, B, C, and D on the schematic -- relative to the symbols on the actual can -- clearly got Fisher all tangled up in its own underwear (at least it did with my Custom Electra VII), as the circuit design engineers clearly intended the can cap's various values to be connected into the circuit one way, while the production team actually did it another.

Larry -- if you have a copy of the version VII Service Manual for the Custom Electra, I'd love to get a copy of it from you. I erroneously thought I had a version VI, but realize now that it is a Version VII (chassis 590-T). I did not see a complete SM for this version on the Console website (only the power amplifier circuit).

At any rate, the next time you relevant console owners have your tuner/preamp out for service, you might check the wiring of this cap, versus how the can itself is labeled. Odds are, the two terminals of interest are wired backwards.

Dave

 

[larryderouin]

Dave; Check yer email.

Larry