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Nakamichi 480 No power/lamps - has correct volts

G

gnexus

Active Member
Long time AK lurker here only now posting:

This deck was purchased new. It worked like new until put in non-climate storage 20 years ago...

When checked it powered on but had transport seized due to flat spotted belts, idler and badly glued up grease. So replaced belts, idler tire and cleaned & lubed the transport mechanism and recalibrated the control cam. Then it would play tapes but with very low headphone volume which would drop out quickly. Stopping the tape and pressing play would again do same thing - sometimes longer faint audio but then drops off...

The cassette tape I was using was also quite stiff from non-usage and improper non-climate storage. So FFW'd it through several times to loosen it. That fixed the tape. But then suddenly the power totally died. Now NOTHING, not even the VU lamps!

The VU lamps are fine. Both have good filaments and continuity. There is 5VAC going to the lamps but they don't illuminate! (Quite strange! Obviously no current.)

Both P/S fuses are ok. There is 24 VAC coming out of transformer and that's properly rectified to 24VDC and 12 VDC.

There's also 5VAC coming from the transformer and going to the lamp and diode. After the diode I'm showing -7 VDC on my multimeter from there to PCB GND screw. That also seems odd. So maybe I'm not checking that correctly.

I have an Associates Electronics degree. But very little experience troubleshooting PCB's (board jockey...). Currently have no other test equipment available other than a cheap DMM. Also: the available PDF manuals I have (2 different ones) are very poor scans and incredibly difficult to decipher the wiring diagrams.

Any ideas, help or possibly a link to a better service manual would be greatly appreciated.

Thanks in advance.
 
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I would Post on Tapeheads for help trouble shooting the deck. If power died suddenly your power supply is the first area to look at. Have you checked all the boards for cold solder joints? I would be looking at capacitors, resistors and transistors in the power supply. I own several Nakamichi decks that I acquired with issues and it was the power supply and transport needing rebuilt.
 
Thanks.
Tried TH first but TapeHeads doesn't accept my email address... :( So actually was hoping some TH people are here also and could give advice. ;)

Agreed on P/S. Assumed it was PS issues so was checking that. No cold solder joints as it's never been serviced...

Please see update post below for more info.
 
Updates:

The VU lamp issue didn't make sense. I forgot about checking auto shut off lamp. So disconnected VU lamp wires from PCB and connected to 5 VDC P/S (no 5 VAC). No lights! Then checked again for continuity. No continuity! So either my previous tests were incorrect or the 5VDC blew the lamps. (Can 5VDC blow 5 VAC bulbs?)

Then did more tests on P/S voltages. But it's not a separate P/S. It's very difficult to make sense of my PDF manual and/or trace the PCB. Both have very poor visual resolution... Anyway, the 24VDC and 12VDC seem good. 5VDC is impossible to trace...

Then reattached the transport and tried the transport buttons again:

NOW HAS POWER!

The sensor lamp is on! PLAY and PAUSE lamps work!

BUT:
REW now runs continuously when button is pressed! (it's supposed to stop after a sec if no tape...). FF no longer works. PLAY no longer works. The sensor lamp goes dim in REW and it goes completely out in PLAY.

The control cam motor works in REC direction (clockwise from front) but no longer works in PLAY direction (ccw from front). Can it be assumed the control cam motor is ok if it still goes clockwise?

If, as is most likely, the cam motor is ok then that would indicate no 12VDC in forward (play) direction. Since also no FF that makes sense. So it seems that either + or - 12VDC is not present depending on which one is used for forward direction. Also no capstan motor. So same situation.

At least the current situation makes diagnosis MUCH easier...

Any ideas, or a better service manual PDF, would be greatly appreciated

It's all a bit screwy...
 
When you press play with no tape in, do the pinch rollers rise up? Cam belt could be slipping. Motor could be dead spotting.
 
Try Analog Alley for good quality service manual scans. It definately sounds like a power supply issue. It sat for 20 yrs in a non climate controlled environment and it was never serviced before. It needs fresh capacitors and reflow all solder joints for starters.
 
There is a good thread on Tapeheads about the same issue and two well known techs helped solved the issue. Contact administrator about your email.
 
Adaboy5 said:
When you press play with no tape in, do the pinch rollers rise up? Cam belt could be slipping. Motor could be dead spotting.
Click to expand...
Definitely not a transport issue.

FYI:
My original post states that transport was serviced with new belts & lubricant on capstan assys, etc. It worked a bit before power loss. The motors all seem good. But no power now in forward direction for ALL motors...
 
Adaboy5 said:
There is a good thread on Tapeheads about the same issue and two well known techs helped solved the issue. Contact administrator about your email.
Click to expand...
Thanks!
Read all the 480 power issue posts last night. Didn't see anything similar then. But today things have changed so probably need to review those posts again.

Plan to contact the admin or get another email to register. But posting here was easier for now.

Solder joints all look ok...
 
I realized just now that the ground wire from transport to chassis wasn't reconnected after I serviced the transport. That possibly contributed to the issue because the transport is screwed onto plastic studs and needs a ground. Looks like that, or just age or a bad capacitor somewhere, caused a motor control transistor (or multiple ones) to die. But it's incredibly difficult to trace the issue. Hopefully the better SM will help. But the circuit descriptions are somewhat lacking details of operation. That has me confused how the DC motors operate in both directions. DC motors require current reversal to go in the other direction. That's normally done by swapping polarity.

It seems no -12VDC power supply is provided. Only +24VDC and +12VDC for the motors. So it's confusing to me how the motors operate in both directions with only a single +12VDC input on one side and a control signal on the other. Maybe someone can help explain how that works?

I noticed just now that the sensor lamp flickers in FFWD (which is not working). No lamp in PLAY (also not working) and dims slightly in REW (works, but stays on with no tape).

No motors are operating in forward direction. The cam & hub motors operate in reverse direction. Cam motor goes to REC when REC is pressed and it returns to STOP position at power on if at FF, CUE or PLAY positions. So seems it's something in common with all 3 motors.
 
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Well the symptoms you described sounds like a dead spotting motor and power supply is bad. I've worked on a total of 6 vintage Nak decks still own 4 and its the transport, motors(cam, capstan) and power supply that need rebuilt. keep us posted.
 
Adaboy5 said:
Well the symptoms you described sounds like a dead spotting motor and power supply is bad. I've worked on a total of 6 vintage Nak decks still own 4 and its the transport, motors(cam, capstan) and power supply that need rebuilt. keep us posted.
Click to expand...
The motors all seem ok. Certainly all 3 motors wouldn't go bad at once and definitely not in only one direction. If they work in one direction they'll definitely work in the other if the polarity is correct. So it's definitely an issue with the power supply or motor control transistors.

Looking at the circuit diagram it seems there's really no separated "power supply" per-se. 24VAC and 5VAC comes from the transformer. The 24V goes to a rectifier and the 5V goes to a diode or two. That's about it... The 24VDC later gets stepped down to 12 VDC for the components that need it. It's fairly simple and the voltages seem ok. But haven't yet checked under load when PLAY is pressed.

Do you know what was needed on yours to repair the power supply? Did you do the work?
 
gnexus said:
It seems no -12VDC power supply is provided. Only +24VDC and +12VDC for the motors. So it's confusing to me how the motors operate in both directions with only a single +12VDC input on one side and a control signal on the other. Maybe someone can help explain how that works?
Click to expand...
Here is a description of how the reel motors have either +12v or "-12v" across the motor to turn in different directions.
1785724161888.png
 
Yes I did the work. On my CR-7 two Shoie capacitors failed and took out two fusible resistors, zener diode and two transistors. And serviced transport.

ZX-9 two capacitors on the motor board and reflowed four transistors on that board get hot, had cracked joints. Also new caps in power supply, serviced transport.

RX-202 capacitor failed causing counter to be intermittent and none of the controls responded.
 
dankik said:
Here is a description of how the reel motors have either +12v or "-12v" across the motor to turn in different directions.
View attachment 3811703
Click to expand...
Thanks for that!

Saw that before in the manual but didn't quite make sense to me. But your highlights help to clarify it.

So it's the difference between the 24 and 12 which gives the -12! Now it makes more sense!

Also noticed in the "control motor drive circuit" that there's both "+24V" and "+24VS." The "+24VS" is for signal instead of constant +24VDC.

Now just need to find the common denominator between all three motors that prevents them turning...
 
Adaboy5 said:
Yes I did the work. On my CR-7 two Shoie capacitors failed and took out two fusible resistors, zener diode and two transistors. And serviced transport.

ZX-9 two capacitors on the motor board and reflowed four transistors on that board get hot, had cracked joints. Also new caps in power supply, serviced transport.

RX-202 capacitor failed causing counter to be intermittent and none of the controls responded.
Click to expand...
Nice decks and nice work!
I used to have a CR-7 at one point. Very nice deck.

The 480, on the other hand, is an earlier low end model. They still sound great. But not worth a huge effort to resurrect, unfortunately. They probably also have a much simpler power supply.

I started working on it now because thought it only be belts, etc. Thought it would be easier than fixing my 580 with no audio... Go figure... :/
 
Yeah Im working on a K-2000 now. The old glue in the power supply turned corrosive/conductive and damage capacitors and legs of couple transistors. Lots of weak solder joints Heads are in great shape though. Its playing and recording pretty good. You still own the 580. I had a 581 was my first Nak.
 
gnexus said:
REW now runs continuously when button is pressed! (it's supposed to stop after a sec if no tape...).
Click to expand...
Check the voltage on Q428 collector. It should go to 0v when you get to tape end.
See my highlighted parts.
1785732590810.png
 
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