Discussion in 'Tape' started by Bigerik, Mar 18, 2012.
Mark the AAACs for easier accurate alignment, clean the old grease and lube out!
PB head Tilt adjust. In order for the record head LEDS to light, on the decks with adjusting rec heads, you have to switch the ground wire right to the metal of the head.
That is friggin brilliant!!!!
Yes, that caught me by surprise the first time, a few decks back. I could clearly see the contacts touching the head and had a good ground, as the PB head LEDs lit. Just needed a better ground to complete the circuit.
Well, my success got rained on. I always run a restored deck as much as possible afterwards, because, well, that's what the owner is going to do. If it starts acting up after 20 hours of use, I want to catch it, if I can. Sometimes, that's a problem (like with the reel motors on the Sankyo transports. The more you use them them better they are. let them sit a few weeks, and poof! they start acting up again). For some reason, the left channel has gradually declined to around -6dB at 20kHz, while the right channel remained stellar. Time for some more investigation...
EDIT: Well after a week of delays, I finally got down to more diagnosis on Eriks deck. I recleaned the heads thoroughly, de-magnetized again, and then checked alignment. I was surprised that there was some oxide evident on the swab, as I had done a pretty thorough job cleaning it. Apparantly, not as well as I thought, so I continued a good healthy scrub with swabs and American Recorder S-721H. After this I still found the PB head left channel is down a few dB over the right, at 20kHz, but not enough to warrant replacement especially for the associated cost. I concluded this by simply exchanging L&R connections on the plug from the PB head to the connector on the main board. The right channel "electronics" were now showing -4db, with the left plugged in there, where with the right it was at 0dB (all references from -20dB). Oddly, the PBH right channel showed -2.5dB in the left channel electronics. So the gain on the left channel, AND the PBH left channel are both lower than the right, at high frequency. They are dead even at 400Hz at both -20 and 0dB. I started replacing all the electrolytic caps associated with both channels playback. Gained about a dB there. Then I rechecked the 10kHz level and decided that I would max out the EQ adjustment there, as I had left the originals in and it was low, but within spec. So I replaced the resistance values for the gain amps, and then re-adjusted the LC filters. After all this, I rechecked head height and azimuth, and was able to finally balance L&R to about -2dB at 20kHz, which lessens to about -1dB at 10kHz.
Subsequent replays have not shown any drift, and auto cals are right on the money. It sounds like a Nakamichi should, and recordings are indistinguishable from the sources. Both Dolby B and C perform very well, on pre-recorded tapes, and on recordings. Actually, I never gave it much thought, but on the decks like this, with only one dolby set used for encode, and then decode, it would make sense that their own tapes would be decoded more accurately than a deck with two separate sets doing encoding and decoding. I just need to record a calibration "as left" tape, and the deck can go back to Erik.
Erik, do you have a copy of the user manual? I don't and wouldn't mind one. I bought the service manual, just to do your deck.
Wow Perry ! I am in total Awe of you man ! Given my complete novice stature I really appreciate what you do and I hope to be at 10 % as good as you in the future. Keep up the great work
Indeed. That is very awesome detailed information. I wonder if I should have my Nak MR-2 looked at, though its running fine for me right now.
IMO the best part of having Perry refurbish a deck isn't the incredibly thorough analysis and solutions, it's the passion he exudes about the decks themselves, I saved the emails he sent me on the diagnosis and repair explanations and reread them every once in a while because they're really awesome. What a great advocate for analog to have on this board.
If this is the same perry on tapeheads...he a great guy. In Va at least...
Perry is a great guy!!
Perry is indeed a great guy. And does amazing work. Been too damn busy to post an update to this thread. I will try to make that a priority ASAP.
My comments on the end result can be found here:
I had a 680 i wanted fixed. Sent it off to somewhere else (not going to cause problems, so I won't say who). I just wish I had known about perry then. He fixed my zx-9 and I love it. I guess i SHOULD HAVE demanded the deck be returned. I actually sent emails and talked on the phone. Maybe posting this again will p me off enough to get on the ball and do something about it. If it is junk i wanted perry to have it for parts. :dammit:
I can't recommend him or his work more highly . Truly the best repair experience I have had.
PerryinVA, do you service Pioneer Reel-to-Reel decks?
No, I do not, sorry.
Thanks here for an excellent discussion. Lots of valuable information for the Nakamichi 681 ZX restorer here. Threads like this one are Audiokarma at it's finest. Many thanks.
Is Perry still around here?
Yes, I replied to your 680zx thread.
Do you service Sony TC-756 RTRs? Thanks in advance. Cheers!!
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