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Nakamichi 480 power supply issue (control cam)

dankik said:
PCB mounting holes 10mm with 2.0mm mounting holes
Click to expand...
Thanks! :)

No. The PCB holes are much smaller. 1mm.

All the 10mm caps I saw on both DigiKey and Mouser were snap in. So it looks like I must just go with 7mm spacing. The leaded ones are all that size now instead of the larger older size. That's no big deal. The 7mm ones will fit ok in 10mm holes. I was more bothered by the 12mm one. I didn't know yesterday there were 2 sets of PCB holes. That makes it much better and not so sloppy looking. :)
 
The play lamp on the new deck was already burned out! Totally black! That made it very easy to fix! :)

But:
Now the play lamp is still on, quite dimly and nowhere near full brightness, in stop mode! :(

Obviously either a bad transistor or bad capacitor leak! The deck still works fine.

It is fully off for 3 seconds after power on. Then it flashes on a single time. Then stays dimly on after exactly 6 seconds.

Pressing pause in stop mode makes stop much dimmer. Then pause is also very dimly lit. Both are then at the brightness of those decorative fake "antique" bulbs where you see the orange filament.

Play lamp is super bright in play mode.
 
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Play lamp issue fixed! :)

It was bad Q418 (2SA733) transistor.

On another note:
The "control cam shimmy" at power on is back.
Obviously the caps from the other deck are also dying.... Didn't even bother to try to check their out of circuit capacitance due to the previous measurement issue highlighted by tdawson.
 
Nichicon long life caps from DigiKey fit perfectly and look original! Even are still Japanese! :)

It also fixes the control cam "shimmy" issue! :)

Other 480 also gets them since its caps didn't fix the issue in this one...
 

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dankik:

Thanks for your help choosing the capacitors! :)

Could you please comment on other 480 thread about recording issues:

G

Thread 'Nakamichi 480 not recording on right channel'

The Line inputs are okay. It has perfectly even line-in audio levels (adjusted with level controls) and equal audio output and VU levels on both channels. This is from a 400 Hz test tone on line-in.

The Left channel playback works fine. But right channel has no audible output after record (it's only a 2 head deck so no actual tape monitor output during recording...). The tape was also tested on different deck (580) and only the left channel was recorded.

This is with a standard 400Hz test tone calibrated to the red lines next to -10dB on the VU meters. Left channel output corresponds to...

Thx
 
Control cam oscillation is still there! :(

It was same as before when powered up today after replacing the belts. So it wasn't the power caps! (But they did still need replacement)

Maybe next step is possibly swapping the other big cap (C306) although it's for the DC power. Then, if issue is still present I guess (and it's definitely a guess) it could possibly be a funky RC4558. There's also an electrolytic cap next to the RC4558... Need to find all the large electrolytics on power rails.

Need to do more COLD (after 24 hrs power off) voltage tests. But only a minute or less time to make the checks. Then must wait another 24 hrs...
 
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Swapped the other big cap (C306) with other deck. It was also obviously leaking at the bottom. But it made no difference to the control cam oscillation.

Checked power rails. Both 24VDC and 12VDC are now rock steady with no variation even in mV.
 
The control cam oscillation on power up was gone today! :)

The only thing previously changed was to remove and check C421 (22uF non-polarized electrolytic cap). It was possibly reinstalled in opposite direction since it's not polarized.
 
So then now it's no longer oscillating in stop. But now it's oscillating when play button is pressed!

The head jumps up and down and the record lamp flashes on and off... NO fast forward! But rewind is ok.

At least it's consistent and not only at power on...

@dankik
Got any comments or ideas on this issue?
Obviously way more important than just 1dB on 580.
 
Q408 was nearly on fire it's so hot!

And CN-3 came unplugged!
Plugging in CN-3 fixed the FF problem.
Also fixed the problem in play!
 
dankik said:
Check the DCV around Q408.
Click to expand...
Thanks! :)
I checked the voltages there at all those points yesterday.. They were correct and perfectly stable yesterday. Rock solid stable even instantly after power on!

It appears the deck is doing okay now. It was just the loose CN-3 connection. Q408 now seems normal temperature.

The big question is whether the oscillation will return again tomorrow?
 
The very low & distorted record level input issue is back :(

Since it's intermittent it's obviously not blown out inputs as I originally assumed. So MUST be the play/record switch.

Edit:
Wrong! The voltages are EXACTLY the same on both sides of the switch!

Looks like C110/210 may be bad.
No. Just couldn't get correct capacitance reading while in circuit.
 
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"Thought" it might have burned out input level slider pots since basically only possible thing left... So swapped one and issue was gone on that channel... Swapped other and issue was back!

Both sliders have broken shafts & missing knobs.

The slider pots are probably the most difficult thing to get on a 480 without paying too much or getting another parts deck. :( New similar ones not available. DigiKey has 10k Alps slider pot. Maybe can use for parts?
 
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The input problem is actually the play/record switch as first suspected.

But it's not an issue with the record switch itself. The switch itself is fine and all the contacts are good with 0 resistance. The problem is the engagement of the switch. It's often not engaging properly...

Except when you're checking it for engagement. :(

So, actually, the input problem is also associated with the control cam issue! Because the control cam isn't always fully engaging record mode.
 
This deck has control cam calibration issues. If stop, FF/REW and play are correctly calibrated then pause is way off (~1.5V). Only way to correctly fix that is to replace R454 with a resistor that gives the correct voltage. To do that you probably need a HUGE selection of 5% tolerance resistors from around 600-800k.

Had to temporarily "fudge" it and set the play position on the control cam far off to get pause to fully engage the record switch in pause.

Probably a good possibility that the control cam sensor pot (VR601) is dirty... But it's a pain to remove & clean.
Edit:
Transport works fine in other 480 with no oscillations. So can't be VR601.
 
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Recording works perfect now. :)
Hope to get this deck fully working well because it's the best sounding of the 3. REALLY spectacular quality!
 
The control cam issue is back today. So whatever capacitor is causing the issue yesterday must have still had a charge.

It definitely not the control cam potentiometer. The transport works fine in the other deck.

Ordered some 1M ohm trim pots to help find the correct value for R454 pause resistor. Then can order correct resistor. But that's not what's causing the oscillations at power on.

Everything else is done now. So just need to find the cause of this remaining issue.
 
dankik said:
Check the DCV around Q408.
Click to expand...
@dankik
I checked all those voltages before and they were rock stable even right at power on. So the control cam oscillations must be something else.

Any other ideas?

You'd think it would be a capacitor somewhere because it's fine after a minute or less and then is ok for at least a few hours even if turned off. But I'm running out of capacitors to replace...
 
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