Magnecord reel to reel voltages

[Siemens EL34]

hi Guys, I hope you are well. Currently I am doing a full check/repair on my Magnecord reel to reel deck. The problem I have is that I am getting odd AC voltages (only) at the drive and take up motor, and the motor capacitor winding in certain switch positions. I am following the maintenance guide to check the voltages at different sections and rail pins, for major component faults and motor faults. The guide is very straightforward. Odd readings:

1. at the take up motor capacitor winding with STOP position I should read 0 VAC but reading 75 VAC.
2. pilot light should read 45 VAC and its getting a constant 63 VAC
3. the take up motor capacitor is getting 65VAC only with STOP position where should be 150 VAC and at play forward position 170 VAC where should be 245 VAC

The issues seems to be only with ACs... the DC is more or less OK.

What I have done so far:

1.Cleaned the switches ( No changes after this procedure, everything reads the same)
2. Checked resistors and changed what was out of spec ( no voltage changes after this procedure, everything reads the same)
3. Changed the take up motor cap with a brand new continuous AC motor cap, just to see if I have any difference ( no voltage changes, everything read the same)

I am kind of lost here what else left to check. I feel running out of options.

What I did not change is all the foil wax caps within the bias circuit and around the switches. But these caps for DC mainly or am I mistaken this? could any of these 0.1uf 600VDC rated caps responsible for odd AC readings?

Kindly help me out here if you have a second to look at the schematic, as I am getting really lost here... thank so much!

[shooter]

my brains not fully engaged yet


measure TB102 23 to 24 VAC
re-measure each to chassis, which TP closest to 0VAC ?

[Siemens EL34]

my brains not fully engaged yet


measure TB102 23 to 24 VAC
re-measure each to chassis, which TP closest to 0VAC ?

Thanks Shooter

 TB102 23 to 24 is 115 VAC

The tap 23 to chassis is lower...5.5 VAC and tap 24 is about 109 VAC.

[PRR]

Do the motors spin? Is the tape tension right? Does the light light?

I would not be real picky about voltages.

I would be VERY careful in there because many of these voltages are lethal and also a probe-slip could burn-up irreplaceable parts.

[Siemens EL34]

Do the motors spin? Is the tape tension right? Does the light light?

I would not be real picky about voltages.

I would be VERY careful in there because many of these voltages are lethal and also a probe-slip could burn-up irreplaceable parts.

Thanks PRR,

Yes motors spin, light its up, and the tape tension seems to be OK too. I did record a 1khz tone on this machine and the only problem I had is dB level changes during playback. Not whining or wowing, only dB jumping up and down +/- 3 dBs in random fashion. After this I started to look into this machine and ended up doing a full check following the maintenance guide.

[PRR]

> dB level changes during playback.

That really can't be the motors or lights, can it? I'd be looking for dirty head or flaking tape oxide. And all the usual bad-contacts on pots switches connectors and other parts, especially if level changes when bumped.

[shooter]

any chance you have a test tape laying around?
playback will eliminate the head, or.....


RR was the good 'ol days, sorry, all my test tapes are extinct

[Siemens EL34]

> dB level changes during playback.

That really can't be the motors or lights, can it? I'd be looking for dirty head or flaking tape oxide. And all the usual bad-contacts on pots switches connectors and other parts, especially if level changes when bumped.

yes thats right... :) when i was going through the section of the component testing in the user manual and saw the voltage differences, i thought i have a much bigger problem...thanks PRR

[Siemens EL34]

any chance you have a test tape laying around?
playback will eliminate the head, or.....


RR was the good 'ol days, sorry, all my test tapes are extinct

:)
Sadly no test tape...cleaned the heads, demagnetized too... the heads are in pretty good shape and all in all this deck was not really abused by the look of it.. i am still bothered of 100+ voltage differences at the take up motor.. or should I ignore this? Thanks Shooter

[shooter]

does the notes indicate "what ground point to use?"


AC volts and returns can be different than DC, or just chassis


You said directions say measure with motors stopped, remeasure while it's spinning, then compare to noted voltage
sometime Tech Writers have been known to add lib 


as NOTED by PRR, use caution, getting bit by AC motor drive volts isn't recommended!

[Siemens EL34]

does the notes indicate "what ground point to use?"


AC volts and returns can be different than DC, or just chassis


You said directions say measure with motors stopped, remeasure while it's spinning, then compare to noted voltage
sometime Tech Writers have been known to add lib 


as NOTED by PRR, use caution, getting bit by AC motor drive volts isn't recommended!

Thanks Shooter, I think the best if I attach all the testing notes written in the maintenance guide. There are indications on each section what to measure against it, I did try my best to follow these indications, measured several times. Table A to D. Each section has the play/rewind/forward and stop position.

Haha..yes I know these manuals sometimes contains errors or mis spellings (i found a few within the parts list vs schematic) but these indictions seems to be what it should be or i donno... if comtains mistakes, what is the point asking users to do maintenance testing... :(

I know and will follow your advise and PRR's too, I am super cautions. I dont poke where I should not, using aligator clips on one end...the rail is outside the unit, easy access. Only using right hand, all with cautions. I hev been hit by a half plugged in socket 110v and also over 300 B+ so far twice, that was enough and a good learning curve. I am super cautios. .....

...what do you think of these testing table attached? I did put my readings there.

Table A has also differences at the take up motor and drive, takep common. and pilot light is always more on each table

Table B is spot on, except pilot light

Table C, D has the most off readings

Table E only measured the record indicatior at stop had 10 V and this is DC. Seems to be OK..kind of

Should I really not bothered about these or should I? I really want this machine to be spot on.

Thanks a million.

[shooter]

Any tables for adjustments?


I might be inclined to tweak R111 n R112 with the motor in STOP, set up to measure TB 3 to 4, then rotate a pot NO MORE than say 10 degrees one direction and "see" if there is a voltage change, if not rotate back 10 degrees (where it started). Rotate 10degrees the other way, if NO voltage change, return it 10 degrees back to start position.


might wait for a 2nd opinion though, I have no power since 4pm yesterday so i'm in the middle of cobbling my off-grid system back together
 

[Siemens EL34]

Any tables for adjustments?


I might be inclined to tweak R111 n R112 with the motor in STOP, set up to measure TB 3 to 4, then rotate a pot NO MORE than say 10 degrees one direction and "see" if there is a voltage change, if not rotate back 10 degrees (where it started). Rotate 10degrees the other way, if NO voltage change, return it 10 degrees back to start position.


might wait for a 2nd opinion though, I have no power since 4pm yesterday so i'm in the middle of cobbling my off-grid system back together
 

Thanks... no table for adjustment sadly... the R111 and R112 uuuuh... i am afraid of those 2 huge variable resistors..its not a turning ones its railed variable resistor...according to the maintenance these controls the tape tension circuit. In Table A, there are measurement requirements for these resistors. How can I touch these resistor pins while the thing is on..? all metal screws for adjustments... uuuh...

Will think about this.

Sorry to hear your power is down...hope you can fix it ... must be super annoying.. 

[shooter]

ahh, then they are out for variable Volts adjust.


got a scope?


I finally got the 4 panels, 4 batteries, OutBack n invertor all plumbed up, dorm fridge up n running 40 deg F!!!
Now if the SUN would just quit playing cloud n seek i'd be charging at 7A instead of 1 5 2 1 3 6 4A........ 

[Siemens EL34]

ahh, then they are out for variable Volts adjust.


got a scope?


I finally got the 4 panels, 4 batteries, OutBack n invertor all plumbed up, dorm fridge up n running 40 deg F!!!
Now if the SUN would just quit playing cloud n seek i'd be charging at 7A instead of 1 5 2 1 3 6 4A........ 

Scope sadly no... but i am glad you managed the solar sorted...i only have one for a little vent for the basement studio...

[PRR]

.....invertor all plumbed up, dorm fridge up n running 40 deg F!!!....

I'll send some sun your way.

My cellar freezer is fully powered and chilling to..... 66 deg. In a 66 deg cellar. Not even 20 years old and it crapped-out with a full load of food. So I'm shoveling spoils and calling for a new ice-box.

[PRR]

....R111 and R112 uuuuh... i am afraid of those 2 huge variable resistors..its not a turning ones its railed variable resistor...according to the maintenance these controls the tape tension circuit. ....

Are you familiar with tape decks? Or not? Tape tension can be felt by hand, heard by ear. If it is not WRONG, snapping or spilling tape, don't mess with these resistors. When you get to wow and flutter and speed regulation, tension is important; even then you go by string and fish-scale (or that meter with fingers), not voltage.

[Siemens EL34]

....R111 and R112 uuuuh... i am afraid of those 2 huge variable resistors..its not a turning ones its railed variable resistor...according to the maintenance these controls the tape tension circuit. ....

Are you familiar with tape decks? Or not? Tape tension can be felt by hand, heard by ear. If it is not WRONG, snapping or spilling tape, don't mess with these resistors. When you get to wow and flutter and speed regulation, tension is important; even then you go by string and fish-scale (or that meter with fingers), not voltage.

Thanks PRR, this is a tape deck i never had a chance to work with before. ...tension by hand not so familiar, by ear, yes. Will not mess with these. Thanks!

[shooter]

even then you go by string and fish-scale

yep
most of the tape decks I worked on weighed about 100lbs, rack-mounted at eye level
I had a tool bag just for them, including a dave-modified "gram scale" that I found a head shop 
too many years ago to recall details, If I don't use it, I lose it!

[Siemens EL34]

Hi guys... i think i am getting closer to the right voltages. I did change all the wax cap's. There were 6 inside the oscillator chassis where I also noticed a bathtub 0.1 capacitor which did some tiny and fine line of oil coming out at one of the pin's. This cap is the C108 connected to the bias pot and a coil.

Can this cap be replaced with any 0.1 UF or must be for some reason oil filled or paper in cap?

Thanks for your help again! 

[shooter]

any good modern-day will work.
watch your heat, use some heat sinks or gator-clips high up the cap legs, between the cap and the solder point.

[Siemens EL34]

watch your heat, use some heat sinks or gator-clips high up the cap legs, between the cap and the solder point.

Thanks Shooter! With regards the heat you mean to be careful during soldering not to damage the coil?

[shooter]

careful with the small caps, they are heat sensitive, too much and you can damage them.

[Siemens EL34]

careful with the small caps, they are heat sensitive, too much and you can damage them.

go it...thanks a lot for your help! :)

[Siemens EL34]

Alright...quick update. Changed all the paper caps for the switches and inside the bias circuit, also changed the pot to a fresh 25k to avoid any doubts. Resistors checked; tube socket cleaned again. Checked for cold solder joints, re soldered  the ones looks shady at the bias tube, also checked the cables connecting the amplifier to the deck, re soldered to be sure that is nice and tidy. Checked all the sockets and cable between the preamp and the deck for loos connections and finally the connections of the erase, record and playback heads. After all of these this is where i am at:

1. the voltages in the original question, some of the were better, improved some of them are still off around the capacitor winding.
2. The audio +/- 2 or 4db drop out while recording the 1kHz tone is still happening in a totally random manner
3. the deck works in terms of playback, tension fine, the 1kHz to is nice and even without wow

Everything responds and looks alright except the audio with the 1Khz tone. I do not have much left here to think what the heck is this and why is this happening? 

Swapped bias tubes swapped, preamp tubes, the same... cleaned and demagnetized the head, same..

I did a video of the 1kHz playback after recording the tone. Trying to post i youtube of any of you is interested to hear it/see it...

I completely ran out of ideas here.. please... help! 

[shooter]

do you have any pre-recorded stuff to play-back? NOT recorded with the current deck


maybe temp in a real small signal downstream of the head. the idea is to split the circuit to help nail down the loss

[Siemens EL34]

sadly no...i dont have that..it would only work if a 1kHz to is pre recorded on full track machine i guess. What for sure I can eliminate as source of fault is the preamp. I fed the 1kHz directly into the bias circuit and record head of the deck, played it back into another preamp, same inconsistency and dB jumps up and down randomly.

There are few cap's ...mica's I did not change in the bias circuit. Should I just go and replace every single part now till the last one? God ...its nerve wrecking...

[shooter]

it would only work if a 1kHz to is pre recorded

so if you record music instead of 1k it plays back fine?

[Siemens EL34]

it would only work if a 1kHz to is pre recorded

so if you record music instead of 1k it plays back fine?

well, sort of fine...with dB jumping ....the listener will only hear it if a long note has been recorded. I have an idea...

I don't have a scope BUT I have a Leader AC Milli-Voltmeter for high freqency AC measurement and I can get a 1kHz at 0dB generated.

I was thinking to:

1. hook the Leader up right where the record head input is while setting the amp on record mode feed the 1kHz tone at 0Db assuming this is .775v and record this is to see if the signal out from the bias is jumping or not. If it does, the head is fine and something happening in the bias circuit.

2. If the signal is clean with no dB changes while leaving the head before entering the bias circuit and the preamp in PLAYBACK mode would indicate that something is wrong either at the preamp in playback mode or the bias circuit in playback mode.

3. I could leave out the preamp audio in/out and connect the record head directly to the 1kHz signal at 0dB in and out. Do the same testing and see what happens. This could eliminate the preamp in PLAYBACK mode.

So the above 3 could tell if its the head, or the bias circuit, or it is the preamp in playback mode.

Am I on the right track here? 

[PRR]

> 0Db assuming this is .775v

It won't be 0.775V but it should be STEADY.

I'm thinking bad joints or caps. Like rats, where you find one, there are probably more.

(OTOH, porcupines are solitary except in mating season. This week, my tree.  )