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Reel to Reel Deck Issue

ElectricArt69

Apr 11, 2014
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I have a Teac 80-8 tape deck with a slight issues- when I am in the monitor mode (MONT) it makes a really loud popping noise when I hit the RW, FW, STOP, or PLAY functions. This issue only occurs in MONT mode. I believe this is the cause for another problem I am having, so for now I'm curious to hear some input on this popping issue. I was reading online, someone had said it sounds like a "blocking capacitor" issue. While I have a very basic understanding of electronics, I am in no means an expert, I'm hoping someone can help me figure this out/ direct me to the right parts.

Thanks!
 

Harald Kapp

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Welcome to our forum.
Let's see what we can do...

The "blocking capacitor" is only one trace to follow. A blocking capacitor is a capacitor inserted in series between different stages of an amplifierr (input and output counting as stages too) to block DC current to flow between these stages. Only AC (music related) current will pass the capacitor while each stage can operate on a separate DC level.
A popping sound is often the result of such a capacitor charging very quickly. Example: An audio amplifier mostly uses comparatively big capacitors at the output to decouple the speakers from DC. When you turn on the amplifier, these capacitors are charged to the operating DC voltage which causes a large initial current spike hat is heard as a plopp sound from the speakers.
If a defect blocking capacitor were the cause in your case, I think you'd hear the popp sound once, but not every time you press one of the function keys.

Another possible culprit could be one or more bad capacitors in the power supply of the tape deck. As this tape deck is not the newest any more ;), chances are that the electrolytic capacitors of the power supply (and on every other board) have lost a good deal of their capacity. They can then no longer supply the surge current that is drawn e.g. by the motor(s) on startup, power supply voltage will drop and you hear a plop. That's typical an normally no cause for alarm. Look for any big capacitors in an aluminum can and labeled somethink like 100µF of higher (1000µF, 2200µF etc.).
There are two types of defect:
  • visible: the can is bulged or even exploded
  • invisible: the electrolyte has dried out
In your case it is probably the second effect due to aging of the capacitors. Replace the biggest ones by new ones with the same capacity (in µF) and voltage (or higher, but never lower). Before you fire up your soldering iron, you can check the relevance of this idea by simply connecting a new capacitor across one of the big ones in the power supply.

Take care not to short out anything. Take special care when working in the power supply part of the tape deck. Dangerous voltages may be present even some time after disconnecting the tape deck from mains power! It's a good idea to get experienced help - if only to double check your work.

Regards,
Harald
 

KrisBlueNZ

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Nov 28, 2011
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Hey, that's not a bad piece of gear!

In addition to Harald's suggestions:

1. This popping noise, is it a single pop sound?
2. Is the volume of the popping sound affected by the volume control settings? If you turn all the tracks down to minimum, does it still happen? Is it coming in on a specific track?
3. Do you also hear a pop if you hit the unit with something firm but not sharp? In other words, is it caused by the vibration from the mechanical actions that happen when you push the buttons?
4. Forget the "blocking capacitor" advice. It could equally be the flux capacitor.
5. Can you describe how monitor mode works? I haven't used a machine like that (I used to have a Fostex G16 but that was all automated). What does monitor mode change?
 

ElectricArt69

Apr 11, 2014
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Well to back track a bit..... The popping only occurs once I have started playing a tape in MONT. mode i.e. it pops each time I RW, FW, STOP that tape, and it is only a single pop. As far as something hitting the deck, no.....I simply hit the transport buttons. When I'm playing back a track at a standard listening level, the pop is loud enough to where the speaker cone could blow, that's what worries me. And it happens across the board, not one track in particular.

The way my deck was designed, you have INPUT, NORM, and MONT. modes. Input is pretty straightforward, NORM. is playing a tape back from the record head. Norm mode is how you overdub, BUT (and the manual says this as well), NORM mode could be used to completely utilize the deck (Record, playback, overdub), all off that one setting.
MONT. mode is simply a non-recordable mode (only off the playback head).

The problem with running everything off the NORM mode, is that you cannot properly calibrate.......Which is where the MONT. mode comes into play......You can only calibrate the deck by using the monitor head.......

Long story short, in order to calibrate the deck you have to record a test tone (starting in INPUT mode), then as the tape rolls, switch the deck into MONT. mode (so you are hearing the signal PLAYBACK on the tape and can adjust). The problem: That has not been working for about a month or two.....Each time I attempt to do that, as soon as I switch to MONT. mode, the signal comes in really weak and has a slapback delay sound. This started around the same time the popping did. And the popping issue occurs whenever I use that mode.

After learning that blocking capacitors can affect the input and output signal, I believed that fixing this popping issue would fix the delay issue; because it really sounds like the signal is bleeding through the NORM head and the MONT. head at the same time, like their is a bad component somewhere.
When I am not in calibration mode (what I mentioned above) and am simply playing back a tape normally, the signal comes in fine, but I still always get the popping.

Harald mentioning the power supply also does make some sense-- I have had a few power outages (i.e. where my house has lost power or Ive blown a fuse) and the deck has been shut off while functioning. It was around the last time that happened where the popping issue began.

If I didn't explain something clearly, message me. I can give a more detailed explanation. FOR NOW, my main focus is the popping because I believe whatever is causing that will also be the cause for the slapback problem.

This is significant because as most of you know, if you can't calibrate a deck, it's practically useless.
 

Harald Kapp

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The service manual can be downloaded here.
Page 87 shows the (imho) relevant section of the schematic where the amplifier is switched from NORM to MON mode.
Capacitors C7 and C8 are candidates for failure as are transistors Q1 and Q2.
If your soldering skills are good enough, try swapping Q1 and Q2 and see if the fault "wanders" with the position of the transistors. Try the same with the capacitors.
If the fault wanders, you have the culprits. Get new transistors and/or capacitors and replace them on the PCB.
 

nepow

Jul 18, 2011
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If you turn down the replay monitoring level to zero can you still hear the Plop? Also when you select the various deck functions which create this noise is the tape still in contact with the play back head? just wondering if a muting circuit may be coming in to late possibly!
 

ElectricArt69

Apr 11, 2014
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I have no volume control over the replay head. The Teac 80 is a very dumbed down, simplified deck. I only have the three recording/playback modes, and then individual INPUT volume controls on the channels, that's it. And yes the tape is still in contact with the playback head, that's how I calibrate it? I may have mis-understood that question.

Harald, after looking thru the manual, I have run into one issue. The page you referred me to, is for what I believe to be the individual channel cards. When I look up the photo of the "Rec/Repro Amp." components, they are the 8 individual channel cards. I believe what you want me to look at would be the main control system for the record functions INSIDE the deck, not the individual channel cards??? Correct me if I'm wrong. I'm only asking this because would one bad channel card be the culprit behind the MONT. function not working? I can't see all 8 going bad on me.

This is a photo of the main control board behind a front panel of the deck. The far left blue switch is for the time clock, the 8 blue buttons next to it are for arming the tracks and the 3 to the far right are as follows: INPUT, NORM, MONITOR switches. I believe this is what I should be looking at? If I mis-understood your earlier post I'm sorry, this is new to me. This is "System Control" pgs. 77-78 of the manual.
$%28KGrHqR,!lYE9Iz2wCD%29BPUD9jqfgQ~~60_57.JPG


I uploaded some recordings of the problems. The first one is the popping. Listen with headphones, everytime I click FW or RW that's the popping I get. The second track is the calibration issue. The song starts on INPUT mode and then when you hear the delay kick in I switched it to MONT. and that's what I'm getting, a quieter, delayed signal.
Tape Sounds
 

Harald Kapp

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Clarification: I meant page 87 of the PDF, which is numbered 83 in the document. I don't think the control board is the issue as it doesn't seem to carry audio signals, only control logic.
On the other hand, I'd call it a remarkeable coincidence if the analog circuitry on all 8 channels failed at the same time.
Is the effect on all 8 channels, or ist it more or less prominent on one channel or another?

Do you have an oscilloscope to observe the supply voltages for signs of voltage dips etc.?
 

ElectricArt69

Apr 11, 2014
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The only oscilloscope I had was in my computer in Logic, I used it for Azimuth checks, (even though I could never adjust the heads since they are locked in pretty tight). I have a multimeter would that suffice?
And yes I checked the deck again yesterday, the effect occurs on all 8 channels.
 

Harald Kapp

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A multimeter doesn't replace an oscilloscope. You can try to get a feeling for the stability of the supply voltages, however, by putting the multimeter in AC (!) mode and setting it to a low range (e.g. 200mV). Then measure from V+ to GND and V- to GND (check all supply voltages). The meter should show almost no reading. If it show a good amount of AC on the supply lines, that is a sign for bad capacitors.
If that doesn't help, I'm lost, sorry.
 

shrtrnd

Jan 15, 2010
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Just some other input. I don't have any TEACs, all of my open reels are Akai.
First, I assume you know to clean and demagnatize the heads.
Second, the Akai's use a slide switch, to move the heads to read the channels on the tape. When I get reduced volume on some of the channels, I thoroughly clean that slide switch. On the Akai's that solves the reduced volume problem.
Third, clean the switches used when the popping occurs, to eliminate that as a possible source of the popping sound. A dirty or bad switch will cause the big 'pop' sound.
Fourth (and less likely), is the popping sound in one or all speakers. A bad speake will give you large 'pop' sounds at certain switching, or 'fast attack' sounds.
Not to dimininsh all the above advice, just giving you ideas about what I'd try first, before I did extensive troubleshooting to the electronics.
Good Luck
 

ElectricArt69

Apr 11, 2014
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Yes, I know to clean and demag. The Teac has a switch to engage the tape to the heads, but doesn't really serve a purpose, since hitting play engages it. (Same thing as Stop and Pause on a tape deck = they do the same thing)
I will have to try cleaning the switches, however highly unlikely since the switches work fine in all other modes (Input and Norm)
The popping isn't from the speaker. I used headphones to make the soundcloud link I put above and I know it's not the mixer either.
 

shrtrnd

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The slide switch causes the heads to physically move SIDEWAYS (also). the tape has channels on one side of it for FORWARD, and the other half of the tape has the channels for playing in REVERSE.
The heads may move to contact he tape on a TEAC, I don't know (they don't on my Akai's), but they must also move sideways to pick-up the REVESE tracks.
On the Akai's, when that slide switch gets dirty, I get reduced volume on one or more channels.
Your 'popping' sound is a separate issue.
 

ElectricArt69

Apr 11, 2014
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Uh, the Teac is a 'forward' only deck. One direction. I plan on looking at everything you all have suggested over the weekend, I'm gonna' pull apart the deck and look for bad capacitors first and anything else that looks like it could use a replacement. I'll post back.
 

ElectricArt69

Apr 11, 2014
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Well unfortunately we found no serious issues with the logic board. And also now the slapback is occurring on the NORM mode as well as MONT. But I noticed a new symptom when I was using the MRL to calibrate: All the pots were not working properly on any of the channel cards; For example the MONT. EQ and MONT. LEVEL pots when I would adjust them, they would also modify the NORM EQ and NORM. LEVEL settings. The actual NORM EQ and NORM LEVEL pots did nothing. Neither did the BIAS adjustment on the card. The rest of the pots I could not tell you as I cannot properly test them.
 

shrtrnd

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Have you checked your power supply voltages? It's seems highly unusual for any other one component to be causing all of these peripheral problems.
The HEADS themselves DO wear-out also. Could the heads themselves be the culprit?
 

ElectricArt69

Apr 11, 2014
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I have not checked the voltages. What am I doing specifically? Putting the probes where exactly? I'm a electronic newb ;) . The heads could be a culprit. In which case I'm screwed because I don't have the money to repair/replace them.
 

shrtrnd

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I'm not familiar wth TEAC boards. Most boards will have voltage test points identified. The voltage you're supposed to see at a particular point on the printed circuit board. If you have or can obtain a schematic, the voltage test
points will be identified on that. Barring any of that, get data sheets on some of the components on the board. A particular point on components like IC's or Voltage Regulators, will have specific voltages on that lead. If the voltage
is not correct, the voltages to other componens will be wrong, and will cause circuit problems. Where the power comes in, there will be a 'power supply' section for the recorder. You will have high input voltage dropped to run the recorder electronics, those voltages will be rectified by Voltage Rectifiers/Regulators, which feed the regulated voltages to run the electronics on the board. Those Voltage Rectifiers are what I'd check first. Maybe 5vdc to run the IC's, 12VDC or 15VDC are common (both positive and negative Voltage Regulator types). Those regulated power supply output voltages are important because they supply power to the components you're testing.
You may have multiple problems. The heads may be a separate issue, but I'll mention I knew a lot of guys who had TEACs, and it was common to have to replace the heads which wore-out when the recorder was often-used.
I got the Akai's because they have glass-ferrite heads, and last infinitely longer than the standard recorder heads. I'd check the power supply voltages (particularly the voltage regulators; if you don't know what they are, Google the
component part numbers, and you'll find them). THEN, worry about whether the heads are too worn or not. Good luck. People here will answer if you have specific questions about how to troubleshoot components.
 
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