Any MCI tape machine users here?

[evm1024]

Soon you are going to want some tape....

I'm selling my 1" 16 track soon. This means that I will have a few gold 996 precision hubs and a handful of 499 reels of tape that can either go with the deck or be traded off. A 996 reel makes a great take up reel and the 499 is good for tracking. What I'm interested in is ATR tape in 1/2" pancakes. If you are interested in trading drop me a pm with terms.

Regards, Ethan

 

[briank]

I didn't get most of the drawers back to life until I hooked the ALIII back up (had it unhooked while sorting out the transport; took so long I forgot all about it lol!) Got me why that would make any difference since the channels are all switched to "local" on the audio motherboards, but it did.

Let's hear it for calibration! Well...I got as far as Rep Cal...got channels 2-8 set but I can't get any level on the channel 1 meter at 1khz...I've got a little level showing on the VU at 10khz (found this out when our short MRL ran out of 1k trying to set ch1 lol) but turning the trim pot doesn't bring it up any...so that's where I'm stuck now.

I did resolder all the ch1 cards, cleaned all the Molexes including the head connections (only thing I didn't do yet was pull out the motherboard to check the soldering because it looks like a PITA hehe)...also thoroughly cleaned the Autolocator connector as it was quite dirty and connectors for other channels were "gotchas"...also fiddled with the remote/local switch on the motherboard, repro/input/cue mode switching on the machine vs remote, pulled and re-seated repro card ICs, even learned from the Right Tension trimmer debacle and gave the Rep Cal trimmer a whole bunch of turns...and I gotta say nothing much changed, I just can't get any level showing on Ch1 for the rep cal...I still suspect the ALIII connection since even after a scrubbing and thorough Deoxit-ing it still seems a bit sketchy but...any ideas?

 

[briank]

Whelp, I took a green scour pad to the Autolocator tuchel and all Molex pins on track one and scrubbed the crap out of 'em until my hands were numb then finished up with some Deoxit (actually I wound up doing all the ALIII tuchels), then pulled the motherboard (not the PITA I thought), re-soldered all the Molexes on it and presto...track 1 back in action.

Now I get to do all the motherboard Molexes for the other 7...and I'm gonna re-solder the rest of the audio cards too for good measure, woo-hoo!

Theeeennn finally I should be able to set up the audio without channels going out intermittently and needing re-seating and whatnot...and then I can maybe actually record something with this beast and see if my efforts have been worth it...I mean, all this time I've kinda just assumed I'm gonna love it

I'll *almost* take the Pepsi challenge with Sweetbeats' Ampex story


BTW, any tips on setting up a 1" MCI JH-110C for Quantegy 499?

 

[briank]

Whelp, every time I start making real progress, another roadblock pops up


The erase head isn't erasing anything and I can't set overbias either...this is a global problem affecting all tracks so it's not likely an individual bias/erase card...basically, I record a test tone onto blank tape, then roll back to the start of the tone, record over it with no input, and when I play back, I only get a quick half a second blip of erasure when the tape starts to roll, then the tone is still there (makes me wonder if there's a bad cap somewhere?)...and when I try to set bias, there's nothing on the meters and turning the trimmer pots does nothing...I'm stumped.

I did check the oscillator frequency and it was perfect...got no voltage at J10 pin 3 on the audio motherboards, though.

 

[sweetbeats]

I ain't no MCI guy, Brian, but you got proper frequency coming out of the oscillator but what is the voltage? Is that what you are talking about with J10 pin 3? Is that the output of the bias amp?

 

[briank]

Yeah. Here's what the manual says, as part of the Erase Adjustment procedures:

[first it instructs how to check the oscillator frequency, which I checked and it's bang-on correct at 120khz]

Next, it says:

"To perform a wave shape and amplitude check, proceed as follows:

1. Connect an oscilloscope to C1 on the mother board [that's the erase peaking trimmer][the oscope showed me different waveforms on channels 1 and 2 so this aroused my suspicions straight away...]

2. Connect a volt meter to J10 pin 3.

3. Set the oscillator gain pot (R9) on the strip board for a meter reading of 1.75 V rms [but the voltmeter barely shows anything at J10 pin 3 and turning R9 doesn't do anything]

NOTE: Changing the 120khz oscillator gain disrupts the bias alignments. The bias adjustments MUST be preformed if R9 is turned [but the bias adjustments can't be done anyway so this is an indication that the problems are connected...]

4. Monitor the erase voltage on erase peaking capacitor (C1) on the audio mother boards [nada]

5. Turn C1 throughout its range... 7. Adjust C1 for peak voltage on all channels. This voltage should be 40 V rms or greater [but it ain't]


I guess I'm needing to better understand the relationship of bias and erasure and how the oscillator works on this machine--and what problem related to it would cause the erase head to not function (we may assume that the head itself is OK). The manual isn't quite as concise on this stuff as it was on the tension system so consulting the manual has only left me scratching my head and begging for mercy lol....

 

[evm1024]

What meter are you using to measure the RMS voltage - does it work at 120 KHz? RMS is 0.707 times peak voltage so you can use your scope to check the RMS voltage. (1.4 x RMS gives peak voltage)

Regards, Ethan

 

[briank]

What meter are you using to measure the RMS voltage - does it work at 120 KHz? RMS is 0.707 times peak voltage so you can use your scope to check the RMS voltage. (1.4 x RMS gives peak voltage)

Regards, Ethan

Hm, good point...I was using the same multimeter (kind of like a Fluke-ish knockoff as far as features but not sure if it's "true RMS") I used to measure the 120khz oscillator freq so assumed I was ok...in any event, it didn't read anything close to high enough voltage at the test points.

 

[evm1024]

Hm, good point...I was using the same multimeter (kind of like a Fluke-ish knockoff as far as features but not sure if it's "true RMS") I used to measure the 120khz oscillator freq so assumed I was ok...in any event, it didn't read anything close to high enough voltage at the test points.

THe Fluke 77 is rated 2% accurate up to 1KHz. Getting a DMM to give accurate AC readings at 120 KHz is quite tough. Not many meters will do it. You might be able to look up your meters AC frew response in the user manual. Till them your scope is your best bet.

REgards, Ethan

 

[briank]

THe Fluke 77 is rated 2% accurate up to 1KHz. Getting a DMM to give accurate AC readings at 120 KHz is quite tough. Not many meters will do it. You might be able to look up your meters AC frew response in the user manual. Till them your scope is your best bet.

REgards, Ethan

Thanks Ethan, I'll give that a try-

 

[briank]

Soooo....just when you thought this thread was dead


I figured out the erase problem, but I need help on the fix:

The problem turned out to be that I have to physically HOLD the RECORD button DOWN to get erasure...that's why I was only getting blips of erasure when I hit the button! I though it must just be a bad Record button, but it's exactly the same deal using the Autolocator, so it's not just a bad switch. I'm suspecting it's a control logic issue but I did a bit of continuity checking and pin re-seating on the logic card but nothing jumped out at me...

Any ideas on why it only works if I hold the REC button(s) down? Aaaack, I'm SO CLOSE!

 

[evm1024]

Soooo....just when you thought this thread was dead


I figured out the erase problem, but I need help on the fix:

The problem turned out to be that I have to physically HOLD the RECORD button DOWN to get erasure...that's why I was only getting blips of erasure when I hit the button! I though it must just be a bad Record button, but it's exactly the same deal using the Autolocator, so it's not just a bad switch. I'm suspecting it's a control logic issue but I did a bit of continuity checking and pin re-seating on the logic card but nothing jumped out at me...

Any ideas on why it only works if I hold the REC button(s) down? Aaaack, I'm SO CLOSE!

OK, just checking - You did push the ready button on the channel electronics. (safe and ready toggle) This is how you enable erase and record operations.

--etthan

 

[briank]

OK, just checking - You did push the ready button on the channel electronics. (safe and ready toggle) This is how you enable erase and record operations.

--etthan

Yessir. I caught a quick low-qual vid of it: http://youtu.be/Q1OGmg-Gul8

[video=youtube;http://youtu.be/Q1OGmg-Gul8]video[/video]

Hm, one thing I just thought of is that the Remote/Local switches (the red "sideways" ones) on the audio motherboards are currently switched to Local...

Other thought is that it could be a batty IC on the logic board...

 

[evm1024]

Had to check...

Ok then the logic board it is. It should latch the record + play button pushes. There are TTL gates forming flip flops there on the logic board. I'll get out the schematic and see what logic diagrams they have. Then you can find ouut which is the record flip flop andd work from there.


--Ethan

 

[briank]

Ok then the logic board it is. It should latch the record + play button pushes. There are TTL gates forming flip flops there on the logic board. I'll get out the schematic and see what logic diagrams they have. Then you can find ouut which is the record flip flop andd work from there.


--Ethan

Cheers Ethan, I'm looking at the control logic schematic and seeing that the "Rec" 7400 IC6 handles Rec Latch (I also see one of those pins goes to a Shield Latch IC, not sure what that is?). I'm also seeing Mom. Rec on IC7, the 7402 "Edit" IC. I checked continuity all the way to the Molexes on either side of the pins associated with the rec latch and mom rec on those chips and that all checks out; however I was a little confused in that I didn't think I was seeing on the board exactly what I was seeing on the schem, but I put that down to lack of experience reading schematics. I guess now it's time to probe those pins with the scope--I'm just not sure what I should be seeing on scope to know whether I'm seeing a problem...

These chips are both at the bottom right corner of the board and the good news is they're both in stock at Mouser...OH, the other catch is these chips are both in black IC sockets. All the other IC sockets on the machine are white ones; I don't know if the black ones are notorious like the red ones? Also makes me think that the logic card is not original to the machine, I'll have to check the card number against the one on the schematic....

 

[evm1024]

7400, 7402, 7408 are standard TTL gates that you might just be able to pick up at radioshack. Hopefully it is IC6 (7400).

When you push play and record does the record light come on? When releasing record/play does the record light stay on? In play mode when pushing rec does the rec light come on (and then go off when rec is released)?

My guess is that the reclrd relay etc on the audio motherboard is OK as that mom rec is working. On the logic board mom rec is handled by IC7.

You should replace IC6 as a shotgun to see if it clears up the problem. To debug it:

IC6 is the record RS Flip-Flop. Normally both inputs (p13 and p5) should be logic level high (a logic level high is +5 volts). During deck power on this Flipflop is reset by pin 13 pulsing low which will cause the FF to latch pin 4 high (pin 4 is rec lo).

So in stop mode we should see pin 13 and 5 high and pin 4 high too. Pin 3 will be low in that case. (pin 3 should be the opposite of pin 4)

When pressing rec pin 5 should pulse low and pin 4 goes and stays low. Pin 3 goes and stays high.

I think that key here is to see if the RS inputs (pin 13 and 5) are both high with no buttons pushed and that they pulse low when they should (pin 5 low to latch record and pin 13 to latch stop/not record) and that the inverter output pin 3 is the opposite of pin 4.

On your scope you should see hear +5 volts DC or near 0 VDC at the pins. A high is above (scratches head, darn this is a long time ago) +2.3v and a low is below 0.8v.

Give that a try and if replacing IC6 does not clear it up than record the logic levels at the pins we talked about as well as the button pushes that caused each level. This a state machine that is dependent on the prior logic state as well as the input button pushes. (I'm thinking about how mom rec would work)

Regards, Ethan

 

[briank]

When you push play and record does the record light come on? When releasing record/play does the record light stay on? In play mode when pushing rec does the rec light come on (and then go off when rec is released)?

The video shows it best; the record light does come on when I put it into play/rec however it turns off when I physically hold the button in, and audio will indeed record to tape without having to hold the REC button in, but I only get erasure if I hold the button down.

My guess is that the reclrd relay etc on the audio motherboard is OK as that mom rec is working. On the logic board mom rec is handled by IC7.

You should replace IC6 as a shotgun to see if it clears up the problem. To debug it:

IC6 is the record RS Flip-Flop. Normally both inputs (p13 and p5) should be logic level high (a logic level high is +5 volts). During deck power on this Flipflop is reset by pin 13 pulsing low which will cause the FF to latch pin 4 high (pin 4 is rec lo).

So in stop mode we should see pin 13 and 5 high and pin 4 high too. Pin 3 will be low in that case. (pin 3 should be the opposite of pin 4)

When pressing rec pin 5 should pulse low and pin 4 goes and stays low. Pin 3 goes and stays high.

I think that key here is to see if the RS inputs (pin 13 and 5) are both high with no buttons pushed and that they pulse low when they should (pin 5 low to latch record and pin 13 to latch stop/not record) and that the inverter output pin 3 is the opposite of pin 4.

On your scope you should see hear +5 volts DC or near 0 VDC at the pins. A high is above (scratches head, darn this is a long time ago) +2.3v and a low is below 0.8v.

Give that a try and if replacing IC6 does not clear it up than record the logic levels at the pins we talked about as well as the button pushes that caused each level. This a state machine that is dependent on the prior logic state as well as the input button pushes. (I'm thinking about how mom rec would work)

Regards, Ethan

That's superb info! Thanks again Ethan, this is huge help! I'll probe the pins and get some spare ICs to sub in and see what happens-

 

[evm1024]

OK I better take a look at the video so that I know what I'm talking about. I'll see what I can come up with tomorrow.

-_Ethan

Short video. So if I understand you correctly you place a tape on the deck that has a tone on it. IN playback you hear the tone (of course). In record without any tone on input jacks and monitoring the repro head you hear the tone except when you push the rec button.

SO record appears fine (Which is to say that if you recorded another tone of a different freq you would hear that also.) It is just that the erase is not active unless the rec button is pressed.

Is this the same on all channels? If only one or just a few channels then I expect to look at the erase activation logic. If all channels then start with erase control logic. There are more variations.

--Ethan

 

[briank]

OK I better take a look at the video so that I know what I'm talking about. I'll see what I can come up with tomorrow.

-_Ethan

Short video. So if I understand you correctly you place a tape on the deck that has a tone on it. IN playback you hear the tone (of course). In record without any tone on input jacks and monitoring the repro head you hear the tone except when you push the rec button.

Yep, and when I play back I can confirm that the tone is getting erased only when the Rec button is held down.

SO record appears fine (Which is to say that if you recorded another tone of a different freq you would hear that also.) It is just that the erase is not active unless the rec button is pressed.

Exactly. Hmm, yeah you're right, record IS fine...

Is this the same on all channels? If only one or just a few channels then I expect to look at the erase activation logic. If all channels then start with erase control logic. There are more variations.

--Ethan

Yep, same deal for all channels. I'm not sure where to start with erase control logic...the word "erase" doesn't even show up on my control logic schematic, I suppose that's why I got fixated on the rec logic...but we're getting closer!

 

[evm1024]

Something to check....

Erase is controlled by 2 things it appears. The first is the record relay K1 on the audio motherboard. The second being the FET switch Q7 on the bias board.

When you put it into record mode does the record light stay on when you release the record button. I just wanted to be sure on that point as that the record light is controlled by the record relay. If the light stays on then the record relay is in record mode. You might still have a bad relay.... but less likely.

Test J10 pin2 on the audio motherboard - I'm looking for the voltages in stop, play, with the record button pressed and after releasing the record button. This is record mom.

Do the same tests for J10 pin1 (this is record hold).

Record momentary comes in on J10/2 and is isolated by CR1 from there it is joined by record hold (which is isolated by cr16) and goes th S7 the safe/ready switch. passing through S7 it goes to CR4 and thus to relay K1 pin 13. This energizes K1 which then allows record hold to pass thrugh the relay (in on pin 12? and out through pin 8?) through CR16 and thus S and back to the relay coil to lock the relay on. The record light is controlled by a section of this relay so if it has switched the light should be on. And we presume that the other sections of the relay are working....

Record hold not only goes through the relay to latch it but also passes to the bias board through J7/1 where it goes through som shaping circuits (ramp up ramp down) emerging from IC1 pin 14 where it then turn FET Q7 on which then passes the erase signal to IC2 (forming a power amp along with Q8 and 9) and thus back to the audio motherboard, the record relay and thus the erase head.

The test you could do is to see if the record ramp control signal onthe bias board (which comes from record hold) goes high (+22v) when the record button is pressed and stays high when the button is released.

You can also check with your scope bias board IC2 pin2 in play, record press, release of record. This is the bias signal after the FET switch.

Something is not quite adding up here and perhaps these tests will shed light on what is happening.

Sorry that this post is not as informative as it could be. I'm looking at about 3 or 4 subsystems inthe tests...

--Ethan