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 Post subject: Re: Grundig YB 400 Troubleshooting- What's Next?
PostPosted: Mar Sat 19, 2022 3:58 pm 
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Joined: Aug Thu 06, 2020 7:46 pm
Posts: 239
Location: Morro Bay, CA USA 93442
Project Update:

- I have replaced C147 and replaced Q41 again for good measure. Front panel is now fully operational with the exception of the on/off button which is still a bit intermittent. But the radio section is powering up and I can see a number of stations coming in based on the tuning bar and stereo indicator.

- Only problem is I can't hear those stations through the loudspeaker or earphone jack.

- Did some work with a signal tracer and found strong audio coming through C117 and C119. But voltages at IC7 are basically all at zero except for the 9V coming in from C147.

- I thought C138 could be responsible for the voltage problems at IC7, so I pulled and replaced it but didn't help. I'll next take a look at C141 and C142, and check the traces/solder joints around IC7.

Looking for ideas; why no voltage at IC7? Could I have blown the chip? Or did it just die? Or could it be one of the surrounding components? Most likely it's the chip, I'm thinking.
ALSO: Looking for a source for a replacement IC7, Sanyo LA4550. I see a few used on eBay, though I have no idea if the sellers are reputable.

Thanks for reading! ~Bill A.


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 Post subject: Re: Grundig YB 400 Troubleshooting- What's Next?
PostPosted: Mar Sun 20, 2022 12:52 pm 
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Joined: Jul Wed 22, 2009 3:07 pm
Posts: 956
Hi Bill,

The audio output is also switched by the audio output jack, when a plug is inserted it switches over from mono to stereo.
That switch could be dirty. I needed to squirt some contact cleaner into the jack of my radio, it is still intermittent at times...

If you do not see the voltages on the audio amp IC as indicated on the schematics, chances are that IC is faulty.
There are equivalents to that chip, the KA2206B, and the TA8227P are two of those. It is possible that it is easier to find some of those.

Regards, Peter


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 Post subject: Re: Grundig YB 400 Troubleshooting- What's Next?
PostPosted: Mar Sun 20, 2022 3:57 pm 
Member

Joined: Aug Thu 06, 2020 7:46 pm
Posts: 239
Location: Morro Bay, CA USA 93442
Thanks so much Peter. No problem finding the new 2206B chip; any tips for getting the old one out? Looks like it might be a bit of a chore! ~Bill


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 Post subject: Re: Grundig YB 400 Troubleshooting- What's Next?
PostPosted: Mar Mon 21, 2022 1:00 pm 
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Joined: Jul Wed 22, 2009 3:07 pm
Posts: 956
Hi Bill,

I do not recall having trouble getting out that chip.
I probably used (it was some time ago) a Weller desoldering iron, one with hand suction bulb on it (it is really just a toy) and solder wick.
Luckily that PCB is only single sided.
Do not overstress the PCB, the traces might get damaged!
On another board I cut all the pins of a DIL chip that needed replaced and then removed the pins one by one. That was a two-sided PCB with plated holes.
Probably that is the "gentles" way of removing an IC with regards to the PCB.
You could use a Dremel tool with a small cut-off wheel to carefully cut the pins. You can not cut the wide cooling flag of the IC with a side cutter.

Good luck, Peter


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 Post subject: Re: Grundig YB 400 Troubleshooting- What's Next?
PostPosted: May Wed 04, 2022 10:02 pm 
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Joined: Aug Thu 06, 2020 7:46 pm
Posts: 239
Location: Morro Bay, CA USA 93442
Some very good news, and some not so good news to report.

- Replacing C147 and IC7 (along with Q41) has restored full function and audio to the radio.
- Remaining issue which I am still troubleshooting: audio in left channel is considerably softer than right channel. Or course this isn't a problem when using the internal speaker, but it does affect the headphone jack.
- New problem: while troubleshooting the left channel issue my DC power supply had an issue and sent a large voltage surge to the radio, which was turned off (in standby/clock) mode. I saw smoke and shut down quickly, but not before IC6 (the voltage regulator) got smoked.

- I have had no luck finding a replacement for this chip and looking for any advice/suggestions. More info below. Thank you! ~Bill A.

RH5RA50AA voltage regulator chip.
RH5RA50AA is a 5.0V Ā±2.5% voltage regulator with a maximum quiescent current of 1.0Ī¼amp.


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 Post subject: Re: Grundig YB 400 Troubleshooting- What's Next?
PostPosted: May Thu 05, 2022 12:13 pm 
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Joined: Jul Wed 22, 2009 3:07 pm
Posts: 956
Hi Bill,

I gave a link to that chip in a previous post. Here it is again:
https://www.digikey.com/en/products/detail/nisshinbo-micro-devices-inc/RH5RE50AA-T1-FE/10214824?s=N4IgTCBcDaIEoAkCscCiSAMBBLBaAKgIy4BiqIAugL5A
You should order the "Cut Tape" version part number and get a few.

Regards, Peter


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 Post subject: Re: Grundig YB 400 Troubleshooting- What's Next?
PostPosted: May Thu 05, 2022 6:52 pm 
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Joined: Aug Thu 06, 2020 7:46 pm
Posts: 239
Location: Morro Bay, CA USA 93442
Peter, thanks. I completely forgot about your earlier post. I'm ordering form Digi-Key and will let you know how things turn out!


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 Post subject: Re: Grundig YB 400 Troubleshooting- What's Next?
PostPosted: May Sun 08, 2022 5:32 pm 
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Joined: Aug Thu 06, 2020 7:46 pm
Posts: 239
Location: Morro Bay, CA USA 93442
Radio update post external power supply voltage surge event and blown voltage regulator
- Blown Voltage regulator replaced and 5V output is verified. 9V OK at audio amp too.
- Audio from radio still the same, no left channel sound (or very little)
- Using signal tracer, signal at pin 5 is much louder than at pin 9, in fact I can't hear 9 at all
- Tried briefly shunting capacitor C119, have yet to tack the new capacitor in place. But handheld, there was no audible change
- Signal tracer shows that C118 and C119 have matching levels of signal, so both channels are making it that far
- The radio's main LCD display is now looking a bit weird, contrast is off and sometimes it flickers, though is visible from an angle
- Hearing some intermittent loud oscillations in the speaker, and frequency might be off a touch on FM. Unsure about this.
--These last two points are making me think there's some possible damage to the radio from the voltage surge, perhaps the microprocessor, or perhaps an intermittent connection of power to the LCD display?? Not sure what circuit that might be.
Thanks for reading! ~Bill A.


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 Post subject: Re: Grundig YB 400 Troubleshooting- What's Next?
PostPosted: May Tue 24, 2022 11:28 pm 
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Joined: Aug Thu 06, 2020 7:46 pm
Posts: 239
Location: Morro Bay, CA USA 93442
PLEASE SEE NEXT POST; THIS WAS SUBMITTED IN ERRO


Last edited by billalpert on May Tue 24, 2022 11:36 pm, edited 1 time in total.

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 Post subject: Re: Grundig YB 400 Troubleshooting- What's Next?
PostPosted: May Tue 24, 2022 11:35 pm 
Member

Joined: Aug Thu 06, 2020 7:46 pm
Posts: 239
Location: Morro Bay, CA USA 93442
Radio Update:
- Recovered from voltage surge with a freshly installed IC6.
- Removed a damaged Q39, as it was causing left channel audio to drop severely when heard through headphone jack.
- Radio is playing well, though apparently there was some lingering damage from the voltage surge
- LCD display contrast is weaker, especially when in FM stereo mode.
- while reassembling cabinet, the 4 wires leading to the ferrite bar became separated from the PCB. Yikes, I tried hard to prevent this.
Question:
There are four leads from the ferrite. Red and Green show continuity, as do the remaining two, though there's about 25ohms resistance across that coil. There are two coil sections on the rod.
I believe red and green are the small coil, and the remaining black/tan wires are from the larger coil section.
But it's entirely unclear which of the 4 PCB antenna connections should be used be each color. Any help appreciated!!
- a photo of the 4 stray leads: https://www.dropbox.com/s/w82a9b8t8onp8 ... s.jpg?dl=0
- the relevant section of the schematic: https://www.dropbox.com/s/ro9adski8abu5 ... x.png?dl=0

Regards, Bill A.


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 Post subject: Re: Grundig YB 400 Troubleshooting- What's Next?
PostPosted: May Tue 31, 2022 6:20 am 
Member

Joined: Aug Thu 06, 2020 7:46 pm
Posts: 239
Location: Morro Bay, CA USA 93442
I resolved the antenna connection issue, plus a problem with the power on button traces and I'm back in business on this now vintage radio.

Closing Post and Final Video: https://www.dropbox.com/s/hqckqz04mco97 ... l.MOV?dl=0

The Yacht Boy 400 sat in a junk drawer for years, as it had gone dead after a long tenure on my night stand as my "go to sleep" and morning alarm clock radio. I just didn't have the heart to throw it away, even though at the time I had no soldering or troubleshooting skills. Over the last few years, I've learned a lot, and had fantastic and generous support from this group.

This particular project was quite protracted and was complicated by my lack of SMD experience plus a failed bench power supply that caused additional damage. But several transistors, capacitors, two ICs, several PCB board jumps later this baby is once again playing. Like many of us, the Grundig is a bit worse for the wear, but still robust in its ability to keep on kickin'.

As you may be able to hear in the video, the internal speaker does a great job with the audio and the earphone jack puts out a nice clean stereo signal to headphones. The internal ferrite and whip antennas do a nice job pulling in signals. The radio is quite sensitive on the SW bands, has SSB capability and holds its own compared to more contemporary designs. It's pulling in most of the SW broadcast stations I can hear on my IC7300. In short, I'm enjoying having it around the house once again!

Thank you for the help!


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 Post subject: Re: Grundig YB 400 Troubleshooting- What's Next?
PostPosted: Jun Wed 01, 2022 7:04 am 
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Joined: Dec Sat 21, 2013 5:15 am
Posts: 935
Location: Puyallup, WA 98371
I'm glad you got it working again. This has been a slightly frightening read :). I have yet to venture into solid state radio repair, but I will- I have a lot of cool sets that don't work, but I'd love to repair them. My favorite radio is my YB-400. I bought it new (I think it may be the only radio I've ever purchased new). After about 25-30 years, it went silent. Since I value it so much, rather than learn on it, I went to eBay and bought another one (nearly mint) for about $40.00. It's been serving me well for the last 5 years or so. The original is in a drawer. Your post has inspired me to tackle it. They must be less fragile than I thought!

Thanks for the enjoyable thread,

Dale

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 Post subject: Re: Grundig YB 400 Troubleshooting- What's Next?
PostPosted: Jun Sun 05, 2022 5:30 am 
Member

Joined: Aug Thu 06, 2020 7:46 pm
Posts: 239
Location: Morro Bay, CA USA 93442
@Dale, yes, it is a very robust radio. I put it through a lot of unnecessary punishment, though I did learn a lot along the way.

So pull that dead YB out and check out Q41; very good chance your problem is right there. Good luck!

Bill A.
KG6NRV


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