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Nakamichi TA4A tuner has no output
Nakamichi TA4A tuner has no output
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Old 23rd November 2010, 02:43 PM   #11
ZeroG is offline ZeroG  United States
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Quote:
Originally Posted by stephensank View Post
Once you pop the bottom cover, you'll see that nearly all of the cracked & suspect joints are not near the main heatsink, but in the middle & areas toward the sink from the middle. There are various transistors & power resistors that cook the board pretty well. Lots of connections will be cooked so harshly that you'll have to desolder, scrape, then resolder to get good solid new joints. If you examine all the less obvious joints carefully, you'll be able to find other suspects, without having to resolder the whole board. Generally, the controller & tuner boards don't develop bad joints, and the power board on the left is the only other place where bad joints & caps are as common as on main board.
Thanks. If i see anything particularly suspect, I'll photo it. Probably get to it on the long weekend.
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Old 23rd November 2010, 02:50 PM   #12
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Originally Posted by DF96 View Post
I assume you mean it is an analogue receiver for analogue FM signals, which happens to have some digital technology for the tuning arrangements? If so, the Analogue Source forum would be the right one. This forum is for digital sources, which would include digital radio such as DAB (ugh!) in Europe. If it is an FM tuner which uses digital signal processing techniques for handling the FM, as some DAB tuners do, then I am not sure which forum it should be in!
Gotcha. Not sure what kind of tuner it is, but you're probably right about having digital tuning rather than being digital radio. But at this time it's probably up to a moderator to move the thread.
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Old 5th December 2010, 05:52 PM   #13
ZeroG is offline ZeroG  United States
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Default NAK TA4A - Recap, repair, still no tuner

Noting that there were several caps with shrunken casings, I recapped about half of the main board and all of the control board. On the main board, I left most of the Nichicon Muse caps in place, farthest from the major heat sources. In the process, I noted a cracked solder on a cap on the main board, and also re-flowed the solder on several other connections.

Had some issues with getting the ribbon cables to make good connections again. Gratefully, got the control panel to work again after a while.

Still no tuner response. I did notice that the new station memo battery (the new one didn't fit the holes, so I installed it on wire legs) was in backwards, so I corrected it. Now the station call number doesn't show up. Could the reverse battery polarity have damaged anything?

Any ideas where to proceed to get the tuner to work?

Thanks for any guidance on this.
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Old 5th December 2010, 06:22 PM   #14
Mooly is offline Mooly  United Kingdom
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Nakamichi TA4A tuner has no output
It's possible it could have damaged something but also logic circuits can get corrupted and be difficult to reset.

An old trick... remove the battery and all power and run your meter over the control pcbs etc to make sure no caps have significant charge. Now press a piece of tin foil hard over the system control ic pins and any other logic... sounds odd but as a repair tech you might be sursprised how many "faults" this can fix. It helps remove any stray charge. CMOS logic can stay stuck in a wrong state for hours or even days even without normal power. So worth a try... no guarantees of course and yes the reverse polarity may have damaged something.
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Old 5th December 2010, 06:50 PM   #15
ZeroG is offline ZeroG  United States
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Originally Posted by Mooly View Post
It's possible it could have damaged something but also logic circuits can get corrupted and be difficult to reset.

An old trick... remove the battery and all power and run your meter over the control pcbs etc to make sure no caps have significant charge. Now press a piece of tin foil hard over the system control ic pins and any other logic... sounds odd but as a repair tech you might be sursprised how many "faults" this can fix. It helps remove any stray charge. CMOS logic can stay stuck in a wrong state for hours or even days even without normal power. So worth a try... no guarantees of course and yes the reverse polarity may have damaged something.
Well, at least it still works as an integrated amp.

Are you referring to the board I just removed and reinstalled or to the control panel built into the face panel?

Thanks
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Old 5th December 2010, 06:54 PM   #16
Mooly is offline Mooly  United Kingdom
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Nakamichi TA4A tuner has no output
Referring mainly to the IC and logic that the backup battery supplies wherever that might be. As you say you have done a bit of work on it and had trouble with connectors it might be worth going over that again just to be sure.
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Old 5th December 2010, 11:40 PM   #17
ZeroG is offline ZeroG  United States
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Tried the foil from the top. Unit was first left for 4 hours to drain, less than 1 volt detected at the main filters.

No response. Tried the battery again. Not sure what caused this, but even without the battery hooked up, the display now reads "000". At first it read 875, then nothing, now "000."

No idea if that is significant.
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Old 6th December 2010, 07:16 AM   #18
Mooly is offline Mooly  United Kingdom
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Nakamichi TA4A tuner has no output
I don't know is the honest answer. So many possible reasons. If you are 100% sure no problem with connectors or solder splashes etc then that leaves either a true faulty component or still a weird logic issue. I know from experience that it is to easy 99% of the time to condemm a microprocessor etc ... normally you can say whatever the fault is it isn't the micro etc. Has the reverse polarity done something... possible but I would be surprised.
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Old 6th December 2010, 07:32 AM   #19
ZeroG is offline ZeroG  United States
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Originally Posted by Mooly View Post
I don't know is the honest answer. So many possible reasons. If you are 100% sure no problem with connectors or solder splashes etc then that leaves either a true faulty component or still a weird logic issue. I know from experience that it is to easy 99% of the time to condemm a microprocessor etc ... normally you can say whatever the fault is it isn't the micro etc. Has the reverse polarity done something... possible but I would be surprised.
Thanks for your help. I will re-insert all the connectors again and see what that does. I will also let the unit sit again overnight and short the microprocessors with foil (can I wrap each one with wire solder instead? It seems the reason is to short them to reset them, and the solder wire is easier to work with.)

It would be nice to know what each of the flat wire connectors is responsible for.

I was so sure that the obvious cracked solder joint at a capacitor was the problem. Everything else worked but the tuner. Maybe that was it and the connectors aren't seating well. They're not really made to be repeatedly unhooked and reinserted. I will put some deoxit on them. Couldn't hurt.

I'll let you know what I find. Do you think all the Nichicon Muse caps on the main board should also be replaced?

For further restoration I was thinking to replace the main caps. Can I go up a little in value from the existing 12000 uf?

Thanks
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Old 6th December 2010, 07:51 AM   #20
Mooly is offline Mooly  United Kingdom
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Nakamichi TA4A tuner has no output
Suppose you could use wire but I always used foil on the print side of pcb and pressed it over the whole lot.
I looked at the circuit and the backup battery is current limited anyway via 270 ohm ? was it so shouldn't damage anything as such. As to replacing the caps, I wouldn't just do that in the hope of fixing it, you need to find the fault first. You can increase the main caps a little but it probably won't achieve much in practice. The larger the cap, the less it "discharges" between cycles from the bridge. That means the bridge conducts for less time to top the charge up but the current flow is correspondingly higher causing the transformer to run hotter under sustained load. In practice that wouldn' happen with music. No real benefit from increasing them really.
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