Nakamichi TA4A tuner has no output

Greetings!

I'm pretty new here, posting-wise. Hopefully this is the correct Forum for this question. I have a Nakamichi TA4A receiver with a non-functional tuner.

It can be manually tuned to a known station but with no output, not even static. Auto-tune just runs up and down and doesn't stop anywhere. No output from the signal strength meter either.

I understand there is a battery for the station memory, but research elsewhere says a bad memory battery wouldn't be the cause for no output.

Wiggled some of the ribbon connectors looking for loose connections with no result. This was in storage for quite a while, if that helps.

I appreciate any assistance with this.
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
I suspect you'll get more response here in the analogue forum,
Analogue Source - diyAudio

perhaps a mod could move it across ?

As to the fault, well it could anything but as you mention auto tune that implies a varicap tuner so it makes sense to see if the voltage is being swept from around zero to... what ? 15 or 18 volts at a guess as the tuning frequency increases. So rare to get tuner faults tbh... also check for leaky (leaked!) caps. No physical damage to pcbs ?
 
The one & only time I have had a tuner failure like that in a TA-series Nak, it was a bad LA1235 FM IF chip. There are a few other possible causes, though, of course, and this is actually the wrong forum for the question.
The two major issues with the TA receivers were heat-related cracked solder joints on the main board & bad electrolytic caps on the main board, especially those near any heat generating components. Your tuner issue could easily be caused by a soldering issue on the main amp board.
 
The one & only time I have had a tuner failure like that in a TA-series Nak, it was a bad LA1235 FM IF chip. There are a few other possible causes, though, of course, and this is actually the wrong forum for the question.
The two major issues with the TA receivers were heat-related cracked solder joints on the main board & bad electrolytic caps on the main board, especially those near any heat generating components. Your tuner issue could easily be caused by a soldering issue on the main amp board.

Thanks for the responses so far. I placed this here because it was a digital tuner. Should I reproduce it on the analog forum?

Sounds like there's some serious troubleshooting to be done here. Is the FM chip available? How would one test for it?

Any particular caps on the main board to be the likely culprits? There's a hefty transformer in this, so it could be a ton of caps to be replaced. Why on the main board and not on the tuner board?

Thanks again for the responses. I'd really like to restore this piece to full working condition.
 
The easy way to diagnose for the LA1235 IF chip is to 'antenna test' the ceramic filters before it. This assumes, however, that you've already confirmed the board is getting the proper power supply feeds from the main board. The 'antenna test' is to take a small screwdriver, dental pick or even straightened paper clip, and, with your fingers in contact with the metal implement, and muting off, touch each outside leg of each of the little blue, 3 flat pins, ceramic filters that come before the chip. If you pick up a very strong local station, or hear a pronounced change in the output, the LA1235 is ok, and there is a problem in the front end, which will usually, if not bad solder joints in the area, be a problem with the VT(tuning voltage) line from the controller section.
As for caps, the TA series used mostly 'god knows what' brand electrolytics for most of the small values, and they go bad, so far, pretty much only when near heat. Not much heat on the tuner board, but plenty of sources on the main board. If you see any darkened areas of board, pretty much automatically replace any small lytics in that area, and replace any lytics that have any heat discoloration at all. Use Nichicon or Nippon Chemicon for long term reliability & best performance. The darkened board areas are also the first place to find cracked solder joints.
Oh, and the TA-4 was particularly full of that horrible tan glue that lots of makers used to hold bigger components in place for soldering/vibration control. That stuff always darkens over time, and by now has become conductive AND corrosive. So, carefully chip away ALL of that stuff from all boards, especially the big controller board that sits on top of everything.
 
I was wondering if a re-cap would be in order - it's 21 years old. This thing has dozens of small caps. I've already noticed the glue.

Well, time to get out the magnifying glass and get to work. I'll try to check for power to the tuner board. Is there a specific test point you would recommend?

Thanks for the advice.
 
I can't seem to find my TA-4 manual at the moment, but there are usually pin labels next to each board-to-board connectors. The VT line should vary with tuning frequency and should range from something under 10V to near or over 30V as tuning goes up. Can't recall ever seeing a VT fault on a TA that wasn't simply a power supply problem, or just a soldering problem on main or controller board.
 
Thanks for your reply. I removed the uppermost board (with the battery) to replace some of the caps and also the battery.

If there is a soldering issue - would you recommend re-flowing all the solder joints on the entire board, or just those around the connectors or near the heat sink? A solder crack might not show, and I'm concerned that repeated disassembling and reassembling might damage the ribbon cables or connectors.

Here's a link for the manual from Hi-Fi Engine:

Nakamichi TA-4 | Owners Manual, Service Manual, Schematics, Free Download | HiFi Engine
 
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.
 
I placed this here because it was a digital tuner. Should I reproduce it on the analog forum?
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!
 
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.
 
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.
 
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.
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
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.
 
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
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
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.
 
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.
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
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.
 
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
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
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.