Schematic vs parts list - what trumps what?

[62vauxhall]

I'm re-visiting a project I abandoned a few years ago. It's a mint Teac R2R. When I got it, I was told it had a "something burning inside and making smoke problem" which it did do after being on 30 seconds or so. What was being incinerated was at least one wire wound resistor. Not picking up on the fact something was the cause of that, I replaced the wire wounds and burnt one of those as well.

I posted on TH and got what seemed knowledgable advice from a particular poster but I think he was over his head as further correspondence ceased. The advise I followed up to that point was pretty much useless. Now I have to undo what I did which means replacing a bunch of parts to get it back to stock - if that's possible.

So I went to the parts list in HiFi Engine's SM intending to get more wire wounds, gonna need them anyway. The thought occurred then then to see what voltage should be present and looked at the schematic.

At least one resistor does not jive. According to the parts list, it's identified as R8 but I've yet to find an R8 on the schematic - maybe just illegible script and I missed it. However, a resistor of the same value is marked on the schematic as R6.

There is only one such resistor so is it a safer bet to think the schematic is right and the parts list is wrong? There looks to be a typo in one of them.

 

[laatsch55]

Gary, if it's one thing I've leaned, it's that documentation canb NOT be taken as gospel, as soooooooo many revisions of this or that were never documented. The boys on AK taught me years ago, it's what's on the board that is right, if the schematic and parts list agree , well, that's icing on the cake....

 

[Bradrock]

I was going to comment, but now all I can think of is the 20 flight rock!!

Maybe I need to get some honey from that honeycomb.............

Can't remember yesterday, but..................I've got that LP locked dowwn up there!


1972?

 

[laatsch55]

20 Flight Rock??? WTF....

 

[Bradrock]

Lost in the Ozone Lee..................Lost in the Ozone

 

[laatsch55]

Ah.... been there, done that, made the shirt meself...

 

[Gepetto]

Usually the parts list since most schematics are made generic to cover multiple build options.

 

[WOPL Sniffer]

I was going to comment, but now all I can think of is the 20 flight rock!!

Maybe I need to get some honey from that honeycomb.............

Can't remember yesterday, but..................I've got that LP locked dowwn up there!


1972?

Is this a "HUH?" Moment????

 

[Bradrock]

Is this a "HUH?" Moment????

Nah, I've just had Commander Cody in my head since 1972


When I see his avatar I am 'triggered' A macro agression into my micro mind.

 

[BlazeES]

Nah, I've just had Commander Cody in my head since 1972


When I see his avatar I am 'triggered' A macro agression into my micro mind.

I got a good chuckle ...

 

[marcok]

Gary, if it's one thing I've leaned, it's that documentation canb NOT be taken as gospel, as soooooooo many revisions of this or that were never documented. The boys on AK taught me years ago, it's what's on the board that is right, if the schematic and parts list agree , well, that's icing on the cake....

I do agree .
PL 4000 ( 3 versions ) and 2 service manual versions .
PL 400 and 700B ( many versions )
Carver C4000 ( 3 versions )
Carver M 400 ( 3versions )
These are some examples !!!
Solution : study and ask !
Ciao
Marco

 

[62vauxhall]

Nah, I've just had Commander Cody in my head since 1972


When I see his avatar I am 'triggered' A macro agression into my micro mind.

"....My dog died on me yesterday,
and left me all alone.
The finance company came by today, and repossessed my home"

"But that's just a drop in the bucket,
compared to losing you.
And I'm down to seeds and stems again too"

 

[62vauxhall]

Schematic vs parts list

For some reason I thought a schematic would be the more concise of the two. But I too have seen discrepancies comparing diagram with what was physically on a board. In that case though I attributed it to being a NAD thing.

Regarding the Teac I'm pondering now, the schematic has two R6's. One of them is mislabeled as it should say R8.

The wattage of those two components don't match either but at least the resisistances do. The schematic indicates they are one watt higher than the parts list says. If I pursue this, I will go with the higher wattage.

I cannot refer to what resistors were on the board when I got the deck because they got carbonized and replaced.

Last night I noticed something that got me wondering - why? When I quit the work, I had what looks to be an 88 ohm resistor half soldered in where a 3.3 is what is called for. I cannot for the life of me remember why that would be. Unless perhaps that was one of the suggestions made by the TH poster. It also may be I questioned that move and why I heard nothing further.

Between then and now, I learned a bit more about schematics than I used to know which was not much. Am I wrong in thinking voltages should be documented on various parts of the circuit? Because there are next to none on this one. I think I identified what wire supplies power from the transformer and I'll have some time this weekend so will check for what might be present. If I can't make sense of that, I may just abandon this thing for good - sell off a few parts maybe.

 

[WOPL Sniffer]

Maybe on a "new" board things May be kosher, once a dirt bag has monkeyed with it, then nothing is correct. Sometimes the schematics have errors however, they are more correct than a circuit board that has been touched. We were taught in school to go by the skizmo while scrutinizing the board also. Use what you got. After 40 years, its hard to find a virgin.

 

[Netfly]

.. Am I wrong in thinking voltages should be documented on various parts of the circuit? Because there are next to none on this one...

Unless otherwise advised, that is often at the discretion of the person making the schematic. Is he documenting it so he will remember what to look for later? Does he really want people to know how it works? Maybe, maybe not. Usually a separate production test document will contain where to test for what voltages during production test, but that isn't typically shown on the schematic.

 

[rtp_burnsville]

Lee summed it up pretty well..... After playing engineer for several decades I'll just add that sometimes all the docs are all wrong and that design errors have been known to have been manufactured (sometimes for years!). About all one can do is reverse engineer what is found and devise a solution for what the circuit should do. Also beware that replacement parts may not perform as the originals. Sometimes a circuit makes use of a part 'feature' that was never spec'ed or tested. When a so-called 'exact replacement' is inserted things go very bad, very fast.

Robert

 

[62vauxhall]

Glen talked sense yesterday, suggesting a replacement board I saw on e-bay was the best solution so I bought it. Untested, but intact so a $30US gamble. Guess I'll see what happens with this thing in a week or two.