Nakamichi 480 No power/lamps - has correct volts

[gnexus]

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.

The 580 had a very badly seized up transport and a flat idler tire. Now the transport works perfectly after a new tire, cleaning and lubrication. But it has no audio output...

The 580 seems a more daunting fix. I don't have the proper diagnostic equipment for audio troubleshooting. So I moved on to fix the 480.

Also for some reason the RM-580 remote no longer works...

It's a very sad situation!

I need a deck to test the 200+ Maxell, TDK and Nak tapes I have recorded on those decks to see if they're all still ok. I used a $20 Amazon Walkman clone to test the current tape I'm using, which was fine. But the Walkman clone rewinds very slow and I'm not willing to use something that low quality for testing all the tapes.

Any ideas on a decent, rugged, and very low cost used deck for tape testing? It doesn't need to be Nakamichi or superb audio quality. Just something cheap and rugged with a good transport that won't damage my tapes.

 

[gnexus]

Check the voltage on Q428 collector. It should go to 0v when you get to tape end.
See my highlighted parts.
View attachment 3811745

Really do appreciate that help! Thanks!

Do you think that a Q428 problem could also cause the other issues (no PLAY & FFWD reel or control cam power, no capstan motor power, and shutoff lamp going out in play?)

I definitely would have preferred Nakamichi to have used TTL logic ICs instead of all these discrete transistors!

It seems there's a component (or multiple ones) in common that's causing the multiple issues. Since the sensor lamp is going dim/out I would suspect a short in the bad component(s) when those buttons are pressed. Maybe multiple components in PLAY (no lamp at all). If only I can trace it down with little experience and without any fancy diagnostic tools...

 

[Adaboy5]

The 580 had a very badly seized up transport and a flat idler tire. Now the transport works perfectly after a new tire, cleaning and lubrication. But it has no audio output...

The 580 seems a more daunting fix. I don't have the proper diagnostic equipment for audio troubleshooting. So I moved on to fix the 480.

Also for some reason the RM-580 remote no longer works...

It's a very sad situation!

I need a deck to test the 200+ Maxell, TDK and Nak tapes I have recorded on those decks to see if they're all still ok. I used a $20 Amazon Walkman clone to test the current tape I'm using, which was fine. But the Walkman clone rewinds very slow and I'm not willing to use something that low quality for testing all the tapes.

Any ideas on a decent, rugged, and very low cost used deck for tape testing? It doesn't need to be Nakamichi or superb audio quality. Just something cheap and rugged with a good transport that won't damage my tapes.

No need to buy another deck you have two good decks they just need to be sorted out. Then you can play those 200 tapes on already good machines.

 

[gnexus]

No need to buy another deck you have two good decks they just need to be sorted out. Then you can play those 200 tapes on already good machines.

I really wish it was that simple!

The 580 transport is good. But the mainboard was really trashed! Had major moisture damage and needed lots of repairs. Now still no audio after nearly 40 hours repair work so far. That deck also has lots of cosmetic issues. The output level knob needs replacing. So it really needs a donor deck...

I thought the 480 would only need the same transport repairs as the 580. But it almost ate the tape after the repairs (it still needs better cam and capstan belts. Have those ordered now).

But then the 480 audio also didn't work! and now also have the power issue problem...

I'm now getting quite fed up with Nakamichi and their silent mechanism. It would be good to have something rugged that works without the Nakamichi complications. Then at least I can listen to the tapes while trying to fix the Nakamichis...

 

[dankik]

EDITED:
I'm starting to get confused on what is working and what is not working on your 480.
Let me summarize the issues that you have and you tell me what I forgot.

1. REW runs continuously when REW button is pressed
2. FF does not work
3. PLAY does not work
4. Sensor lamp is dim in REW
5. Sensor lamp flashes at normal level in FF
6. Sensor lamp is out in PLAY
7. Control cam works in REC direction, but not in PLAY
8. No motors are operating in the forward direction
9. Cam & hub motors work in the reverse direction
10. Cam motor goes to REC when REC button is pressed, returns to STOP at power on... if FF, Cue, PLAY positions

Did I leave anything out?

 

[dankik]

TEST1: Let's start off by making sure that the transport buttons are all functional and none of the transistors are bad.

1. Do you have +24V on the Q428(e)?
2. Do you have +24V on the Q428(c)?
3. Press the FF button. Do you now have +24V on Q401(c)
4. Press the REW button. Do you now have +24V on Q402(c)?
5. Press the PLAY button. Do you now have +24V on Q418(c)?
6. Press the REC button. Do you now have +24V on Q419 (c)?
7. Press the STOP button. Check to make sure that you no longer have +24V on Q401, Q402, Q418, Q419 collectors.

 

[gnexus]

I'm starting to get confused on what is working and what is not working on your 480.
Let me summarize the issues that you have and you tell me what I forgot.

1. REW runs continuously when REW button is pressed
2. FF does not work
3. PLAY does not work
4. Sensor lamp is dim in REW
5. Sensor lamp is out in PLAY
6. Control cam works in REC direction, but not in PLAY
7. No motors are operating in the forward direction
8. Cam & hub motors work in the reverse direction
9. Cam motor goes to REC when REC button is pressed, returns to STOP at power on... if FF, Cue, PLAY positions

Did I leave anything out?

You're correct!

Also: sensor lamp flashes at normal level in FF.

 

[gnexus]

TEST1: Let's start off by making sure that the transport buttons are all functional and none of the transistors are bad.

1. Do you have +24V on the Q428(e)?
2. Do you have +24V on the Q428(c)?
3. Press the FF button. Do you now have +24V on Q401(c)
4. Press the REW button. Do you now have +24V on Q402(c)?
5. Press the PLAY button. Do you now have +24V on Q418(c)?
6. Press the REC button. Do you now have +24V on Q419 (c)?
7. Press the STOP button. Check to make sure that you no longer have +24V on Q401, Q402, Q418, Q419 collectors.

View attachment 3811985

1. Yes
2. Yes
3. It's 0V when not pressed. Goes to 24V then to 0.
4. Yes. Stays at 24V (because REW stays on)
5. Yes. Stays at 24V
6. Yes. Stays at 24V
7. There's 0V on all.

Also: checked button switches. Only continuity when pressed.

 

[dankik]

Are you sure that you measured the transistor collectors for 3-7 above and not the emitters?
OK, let's check the Q401(b). Should be +24V when nothing pressed and go to close to 0V when FF is pressed.

 

[gnexus]

Are you sure that you measured the transistor collectors for 3-7 above and not the emitters?
OK, let's check the Q401(b). Should be +24V when nothing pressed and go to close to 0V when FF is pressed.

No. Sorry. Was rushed then... Seems it was actually the emitters... Please see above post for updated readings on those.

Q401(b) is at 24V when nothing pressed and goes to 3V in FF.

 

[dankik]

No. Sorry. Was rushed then... Seems it was actually the collectors... Please see above post for updated readings.

Sorry, those measurements were the collectors, or not? If they were already collector voltages, why do you need to update the readings?

 

[gnexus]

Sorry, those measurements were the collectors, or not? If they were already collector voltages, why do you need to update the readings?

Sorry for the typo. Meant emitters in that post.

 

[dankik]

It's 0V when not pressed. Goes to 24V then to 0.

What does this mean? When not pressed, the Q401 EMITTER is 0V, then when the FF button is pressed it goes to +24V, then back to 0V. When does it go back to 0V?
It might be going to 90V because Q428 is turning off because the Shut-off condition is bet and the Auto Shutoff circuit puts 0v on Q428 base to cut the +24VS power to the switches.

OK... now you need to measure what I originally asked for, the collector voltages for each button in post #26 before it is pressed then after it is pressed.

 

[gnexus]

What does this mean? When not pressed, the Q401 EMITTER is 0V, then when the FF button is pressed it goes to +24V, then back to 0V. When does it go back to 0V?
It might be going to 90V because Q428 is turning off because the Shut-off condition is bet and the Auto Shutoff circuit puts 0v on Q428 base to cut the +24VS power to the switches.

OK... now you need to measure what I originally asked for, the collector voltages for each button in post #26 before it is pressed then after it is pressed.

View attachment 3812083

The updated readings are for the COLLECTORS, as you requested. Sorry again for that mistake and also the typo in #30. It's been a long day..

So maybe not the best time for quick troubleshooting tests...

Q401 COLLECTOR goes to 24V and then IMMEDIATELY back to 0. Only happens in FF.
UPDATE: Now it varies rapidly from 12-18V.

Shut off never works! Because ALL modes stay on forever while the take up reel is NEVER turning. I'll check Q428(b) and see if it ever goes to 0V...

Nope! Q428(b) stays at 24V...
Q427(b) is 0. C412 is 0. Q430(b) is 0. Q429(b) is 24V. Q429(c) is 24V.

Q423(b) is 24V no matter if PAUSE is on or off. PAUSE light is on when PAUSE is depressed.

Interesting note:
Bought this deck as "new" from local very reputable high-end audio dealer. Only service has been for counter belt shortly after purchase (how did the counter belt die so quickly?). But looking at the PCB Q422 has definitely been replaced! Thinking now that the dealer sold me a used & repaired deck as "new." Been so long forget if it was in a sealed original box...

That's about enough for me for tonight. I'm getting dingy and will likely short something out if I keep going... :/

 

[gnexus]

So... on goes the diagnostics...

Thanks again to you, dankik, for getting me going

It seems PAUSE is staying on even when the switch is not depressed. The switch operates correctly. So it's something else. But having PAUSE on explains why the auto-shutoff doesn't work because PAUSE disables it.

Looking at the wiring diagram the PAUSE switch goes directly to the IC402(1/2) op amp. That IC also supplies the motor power signals and the +12V power. The IC402(2/2) +12V section is putting out correct voltage but it may not be supplying enough current. It appears the (1/2) section isn't working at all. That would explain why PAUSE stays on and also why there's no forward signal to any of the motors.

IC402 is common to ALL the issues previously described. It seems to be the common factor. So I'm under the assumption it is defective. I've ordered a replacement RC4558D that should arrive tomorrow.

 

[gnexus]

The problem was a defective IC402! Replacing that op amp with another RC4558D resolved the issues!

PLAY mode still needs "coaxing" the control cam by hand due to a bad belt. I'm still waiting on new belts. They should be here soon. I don't want to "strain" the circuitry more. So I'll wait until the belts are replaced for the final tests.

IC402 had a small capacitor across terminals 2-3. I forgot to reinstall it. It's not shown in the circuit diagram. Looks original. Deck was (supposedly) never previously serviced except for the counter belt. Does anyone here know what is the purpose of that capacitor? The deck seems to work okay without it and I don't have a capacitance meter to check it. So should it be reinstalled?

Thanks again to dankik for getting me going!

 

[dankik]

Does anyone here know what is the purpose of that capacitor?

Looks like it's to reduce noise on the opamp input.

 

[gnexus]

Looks like it's to reduce noise on the opamp input.

Thanks! ...and thanks again for the help!

I forgot the other section of IC402 is also used for the audio section... Guess I'll solder the cap back on and hope it doesn't change anything. It shouldn't. It's the other section than the one for the motors.

I'm planning on doing more troubleshooting this weekend on the Nakamichi 580 no audio problem while waiting on the new belts for the 480. Could you possibly be kind enough to comment on that thread and maybe give me some ideas to get started better on the 580? Thanks in advance.

 

[gnexus]

Just now installed the new belts. Now the control cam action is very positive! Just like new!

But then, after testing all the functions, I tried to play a tape. It would rewind and FF perfectly, but play wouldn't engage! The pinch rollers weren't coming up all the way to meet the capstans

So tried to recalibrate the control cam. I'd already readjusted it previously. But maybe the new cam belt changed things... Stop was dead on. But play was at the PS position! Tried readjusting VR603. But it wouldn't get all the way to play even at the VR stop! So then checked the manual, which says to go through extensive fine adjustment procedure checking voltages and replacing resistors

Then noticed the PAUSE button was depressed! LOL!

Works great now! Great sounding audio! Haven't heard highs that clear in a very long time!

But the music test tape I used on it now has dropouts from previously getting eaten by the 480

Thanks again to dankik for helping get it fixed!

EDIT:
Tape has big dropout 10 mins after where it was eaten. That doesn't bode well for all my other tapes

Also:
The right channel output on VU is 10-20dB lower than the left. I don't know if it's the tape or the deck. In addition, I'm noticing a quite apparent odor of baking electronics! It's nothing serious. But it's a bit concerning. Haven't yet tested RCAs or recording...

 

[dankik]

I noticed on my Nakamichi 681ZX and 500 that when I was recapping the boards and cleaning it with isopropyl alcohol the board coating was sticky and also had a distinct smell that was hard to get rid of. I had to clean the boards many times until I removed the coating so it was not sticky, then the smell eventually went away. Maybe they used the same coating on yours? As far as the R channel, have you tried cleaning the tape heads? What happens if you try to record and playback the Dolby test tone? Do the VU meters work correctly?