Nakamichi TA4A tuner has no output - diyAudio
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Old 21st November 2010, 03:15 PM   #1
ZeroG is offline ZeroG  United States
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Default 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.
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Old 21st November 2010, 05:25 PM   #2
Mooly is offline Mooly  United Kingdom
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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 ?
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Old 21st November 2010, 06:17 PM   #3
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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.
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Old 21st November 2010, 06:48 PM   #4
ZeroG is offline ZeroG  United States
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Quote:
Originally Posted by stephensank View Post
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.
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Old 21st November 2010, 07:10 PM   #5
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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.
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Old 21st November 2010, 07:26 PM   #6
ZeroG is offline ZeroG  United States
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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.
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Old 22nd November 2010, 07:30 PM   #7
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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.
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Old 22nd November 2010, 11:30 PM   #8
ZeroG is offline ZeroG  United States
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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
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Old 23rd November 2010, 01:22 AM   #9
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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.
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Old 23rd November 2010, 09:34 AM   #10
DF96 is offline DF96  England
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Quote:
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!
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