Nakamichi 480 not recording on right channel

[gnexus]

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 set record level. Right channel no output and meter wiggling at -40 dB.

Update:
After making the recording I just now noticed that the right VU level and playback audio output is now very low on a tape with known even channels. This wasn't previously an issue. So the issue is very likely to be the record/playback switch. I'll spray some contact cleaner in it and update this thread accordingly once more info is known.

Update 2:
Spraying contact cleaner in the REC/PLAY switch returned the PLAY output levels to even. Confirmed with 400Hz test tape from other deck that has even VU levels.

BUT, the recorded 400 Hz output is incredibly low. Left VU is at -8dB (or whatever the red mark is) while right channels is -40dB. Dolby in/out has no effect. Raising the record input level to 0 raises the left previously recorded output, but it has no effect on the right channel.

 

[gnexus]

The 480 also has very low output on the RIGHT channel. Moving that discussion here from the 580 thread:

The 480 is similar to the 580. The headphone output takes the same Line Out signal and goes through one additional amplification stage before going to the headphone jack. Since you say that the headphone output is good, then the output from the first amplification stage must be because it is common to both the headphone output and line output.

The ONLY difference is that the line out goes through one more capacitor (C245) before going to the Line Out RCA jack.
Check C245 (C145) to make sure it is good. You can also check the board traces and solder.

View attachment 3820864

 

[gnexus]

Then something strange is going on. I pulled both C245 and 145. Both had identical capacitance of 13uF. I swapped the two when reinstalled. Still has same issue with very low right channel.

This board is very clean. Just like new. So no issues with the traces, etc. I extensively cleaned the RCA jacks by scrubbing them with deoxit. The jacks are enclosed in plastic. But has 0 ohms between RCA and PCB.

 

[gnexus]

Turns out the voltage regulator IC was somehow responsible for the low right channel line output. Replacement of the voltage regulator IC also dramatically improved FF and REW speeds!

 

[gnexus]

Assume now that the issue with no recording on the right channel is due to a defective Dolby IC. Most other possible causes have already been eliminated. Will try swapping Dolby ICs to confirm if defective.

 

[gnexus]

Turns out the voltage regulator IC was NOT responsible for the low right channel line output. The following day the low right output was back!

Replaced the 2 Dolby uA7300 ICs with LA2730s. That accomplished NOTHING, unfortunately. (Hopefully at least slightly improves the Dolby NR).
Still no right channel recording..

So then swapped ALL polypropylene caps in Dolby circuit with left channel. All caps had similar and okay values. So no effect on right channel recording.

Also noted that, unlike tape playback, the right channel line output is fine for recording monitoring.

Now running out of possibilities to resolve these problems without a scope...

Any ideas anyone?

 

[tadawson]

Turns out the voltage regulator IC was NOT responsible for the low right channel line output. The following day the low right output was back!

Replaced the 2 Dolby uA7300 ICs with LA2730s. That accomplished NOTHING, unfortunately. (Hopefully at least slightly improves the Dolby NR).
Still no right channel recording..

So then swapped ALL polypropylene caps in Dolby circuit with left channel. All caps had similar and okay values. So no effect on right channel recording.

Also noted that, unlike tape playback, the right channel line output is fine for recording monitoring.

Now running out of possibilities to resolve these problems without a scope...

Any ideas anyone?

Get a scope . . . you have already wasted far more time than it would cost you.

 

[gnexus]

The problem with no recording in right channel was the transistor in the record amp right channel - Q203 was dead.

Problem resolved

So end of this thread.

 

[gnexus]

The problem with no recording in right channel is now BACK!

Unbelievable!!!
It worked fine for a day. Then when powered off and then powered on the next day it was back! Just like the low volume issue on same channel...

I tried swapping Q203 with another 945 transistor to no effect. Also checked the adjacent capacitors. No luck. I already ordered new KSC1845 low noise transistors to replace the 945s. Maybe that'll fix it again? Maybe not... :/

Think this deck is cursed! A 480 is not worth all this effort...

 

[gnexus]

This poor old very long neglected 480 is doing much better now.

Playback on line out is now even and CD quality. Recording on BOTH channels is also working now.
It seems it somehow got WAY out of both mechanical and electronic adjustments just from sitting so long in non-climate storage.. I don't yet have test tapes. So can't do final adjustments, but at least it's much better now.

Unfortunately the right channel recording is still very low. It's 0 dB on left using 400Hz test tone. But right is at -20dB with the recording level pot maxed out

Not sure of the cause yet. Playback is very even now. So wouldn't think it's an alignment issue with a 2-head deck...

 

[gnexus]

The low recording level on the right channel seems to be a mechanical alignment issue as the recording level voltages are even at the tape head. It seems that alignment for recording is much more critical than for playback.

Unfortunately no alignment tapes or a M300 jig to properly set the alignment.

 

[gnexus]

It's not any mechanical alignments. Most all electronic components have also been tested. So now thinking the playback /recording head could be bad. That would explain a lot - like the low right channel output on old tapes previously recorded on this deck in addition to the low right channel recording level. Will swap transports to test...

 

[avionic]

I tried swapping Q203 with another 945 transistor to no effect.

Trivial tip : 2SA945 is ECB pin out. KSC945 is EBC. KSC945C is ECB pin out.

 

[dr*audio]

It's not the head. Your problem is intermittent. Since playback is always ok, the head is not intermittent. Check the schematic to see if this uses a relay to switch the head from playback to record.

 

[gnexus]

Trivial tip : 2SA945 is ECB pin out. KSC945 is EBC. KSC945C is ECB pin out.

Yeah. Knew that. The KSCs I got and tried are KSC1845FTA. Also tried swapping an original 2SC945(A). Neither made a difference although, as noted previously, initially for a day the record levels were ok after swapping in the 2SC945(A).

Very strange problem! Need to at least swap out another transport to isolate the issue.

 

[gnexus]

It's not the head. Your problem is intermittent. Since playback is always ok, the head is not intermittent. Check the schematic to see if this uses a relay to switch the head from playback to record.

Playback is not even on most tapes. Right channel is very low. Had other thread on that before this one. Thought it was resolved. But no. . .

Any of my previous comments on that were either erroneous or after cranking up the right playback level

Playback is always at least -10dB(+/-5-10dB) lower on right channel with most tapes. Only way to resolve that is to crank up the right playback level.

The play/record switch has been cleaned, tested and examined with DMM multiple times. It's fine.

It may not be the head. But at least need to swap another head or transport to isolate the issue.

 

[gnexus]

Just got this deck working again after swapping parts with other "new" one. I discovered on the other 480 that the levels on my rudimentary 400Hz test tape made on the 580 were way off. That 580 obviously needs much better calibrations. It has the better Crystalloy heads instead of the sendust ones on later models. So should be very good once properly calibrated.

That means that to get almost even playback on this one the left channel level must be at nearly minimum and right playback level must be maxed out. Then they are almost even.

That definitely sounds like a bad head...
It's either that or I have a factory prerecorded tape + 200+ tapes made on this deck with (previously perfectly even) now very degraded right output even after recording new audio on a couple...

Wonder what the results will now be for recording?

 

[dr*audio]

Just got this deck working again after swapping parts with other "new" one. I discovered on the other 480 that the levels on my rudimentary 400Hz test tape made on the 580 were way off. That 580 obviously needs much better calibrations. It has the better Crystalloy heads instead of the sendust ones on later models. So should be very good once properly calibrated.

That means that to get almost even playback on this one the left channel level must be at nearly minimum and right playback level must be maxed out. Then they are almost even.

That definitely sounds like a bad head...
It's either that or I have a factory prerecorded tape + 200+ tapes made on this deck with (previously perfectly even) now very degraded right output even after recording new audio on a couple...

Wonder what the results will now be for recording?

I threw out a 480 about ten years ago because nobody wanted it, even for free. If I had saved the head I would have given it to you. Fear, not; 480's are cheap and plentiful. I found the one I eventually threw out in the garbage. It just needed all the rubber parts and I hate working on the Classic transport and didn't need it.

 

[gnexus]

The 480 models are incredibly undervalued and underrated. That unfortunately makes them either parts decks or not worth the repairs. So many, like yours, end up in the trash...

They all use the same Classic transport as the most expensive Naks like the Dragon (except of course the capstan motor, auto reverse and NAAC). Most of the electronics are nearly the same. Even the heads are the same on the 3-head decks. So they sound basically just the same as the higher end models.

The "parts deck" I just bought now sounds so good that I can't tell the difference between a CD and a 35 year old tape of it. Tapes of recorded LPs that are 46 years old actually still sound even better than that! Simply amazing!

I had friends in several very high-end audio boutiques when I was in high school. They all recommended a 480 or 580 for someone like me. I've been perfectly happy with the 480 since then. I also had a ZX-9. But sold it when CDs became affordable. There wasn't much sound quality difference between those decks although the ZX-9 convenience features were nice.

Overall I like my 580 better, but that's mainly because of the extra features and the lack of slider pots. But it doesn't sound as good and, unfortunately, also doesn't record metal tapes.

Later, now that I find the classic transports simple to repair, I might find a Nak that better holds its value and doesn't say Sankyo. But I'll always keep the 480 simply because I love the awesome control buttons.