Nakamichi 680zx calibration issues?

[W4THX]

Hello to all this is audioworkshop1.com we have 2 Nakamichi 680zx decks in for service with the same problem... when we try to calibrate them we can hear the 400hz tone but not see it on the FL meter display either in the source or tape position, the units record/PB perfectly... we have totally overhauled them both and gone thru the calibration sequence from the service manual. Can we be overlooking something obvious here?

 

[perryinva]

So, everything works correctly, in that when the switch is set to “Cal”, the tone is there, but you cannot adjust the front panel Level pots because you cannot see where level is relative to 0dB. Is that correct?

Otherwise, the meters work absolutely correct? Peak Hold works, the correct levels are shown in both Source and Tape in normal use?

Also, the built in 400Hz tone is the correct level at the output jacks in Source?

 

[W4THX]

yes everything works fine we have calibrated the 400hz tone to the service manual specs on tp101/201 to 100mv on both channels but we only have .25vac at the outputs in source and 2 bars on the meter, I assume that's the issue ... were just a little perplexed that we have the same issue with both decks. Were also finding a lot of bad solder joints on that board and redoing all of them now, so far we haven't found any bad caps, but still checking...any advice at this point?

 

[Hajidub]

yes everything works fine we have calibrated the 400hz tone to the service manual specs on tp101/201 to 100mv on both channels but we only have .25vac at the outputs in source and 2 bars on the meter, I assume that's the issue ... were just a little perplexed that we have the same issue with both decks. Were also finding a lot of bad solder joints on that board and redoing all of them now, so far we haven't found any bad caps, but still checking...any advice at this point?

Every one of those orange poly caps, whether you tested it or not (and it tested good), needs to be replaced (even the ones on your meter board).

 

[perryinva]

If you haven’t recapped the meter boards, especially the orange polypropylene caps, that has to be done, as well as all 4700pF ones in the deck. They are always leaking. Replacing all of them would be better, but usually those are the worst. Any 100uf 25V Shoei blue caps should be replaced. They have a high mortality rate. I haven’t looked at the circuit in a while, so have to check. Only 250mV at the output is low, should be 1000mV, but that should still give you way more than 2 bars. 100mV output is -20dB. When adjusting the 400Hz tone level does it react accordingly on the output as well as the test point?