Dreaded HU-650 intermittent FM and possible fixes?

[dikidera]

So the original HU-650 in my car is acting up. I get the dreaded intermittent FM which corresponds to how hot the radio gets. Cold being no-go and hot causing it to work.

The implicated problems are two IC chips under a shield, one chip being SAA7709H/103 and the other of the same family. Some folks have had success by replacing the chip, others say the problem comes back after 1-6 months, so no permanent fix there and the replacement chips are of dodgy quality.

I also know there are two antennas on the S60. One at the rear D-post and somewhere behind the bumper which have also been implicated in the issue.

https://forum.gsmhosting.com/vbb/f179/v ... d-1906082/

https:// www.facebook.com/ggerc/posts/volvo-hu-8 ... 703352835/

https://www.drive2.ru/l/594573833055257956/

I already opened the unit once but didn't fix it the first time. Now my second attempt will use an oscilloscope to check signals going in the chip vs going out.

However notice the chips are used in other car radios, and not once has anyone said of any such defects, only in Volvo radio units. I am still wondering if it's the internal circuitry of the chip that get affected or is it simply a case of bad solder joints somewhere.
The other possible thing I can think of is incorrect circuitry leading to damage over time. This is why chip makers give reference designs that they encourage you follow.

[yanga001]

So one thing i had with my 98 V70 was that some electrical solder connections went bad in the rare manual climate control system. I got intermittent functionality with no functionality in cold and somewhat operations in hot. What fixed it was resoldering the connections.

I suspect that high resistance connections form at this joints either due to a cold solder joint or just time. Reflowing the connections may fix it.

Like you said these chips are normally good and things rarely cause them to fail.

I would attempt a resolder or use a hot air station with wick to clear one side and then resolder it.

I would also resolder any connectors that may have strain or movement over time. Ie the posts that connect to the antenna, the outputs, etc.

Hope it helps!

[dikidera]

This is my second time taking it out, I saw a capacitor for 3.3v that had a broken connection from the many heat cycles, but I doubt this could be the main culprit. I also resoldered all pins of the infamous SAA7709H/103 chip which is implicated in the problems. The chip itself was however covered in some yellow substance that is probably there to prevent moisture from causing corrosion, but this ultimately prevented me from doing a clean resolder so I spent a lot of time with acetone to get it out, and I still couldn't, it's very persistent.

The first time there was some kind of load or power resistors that had broken connections from the power transistors on the other side of the board that causes browning of the PCB. I immediately thought they were the main cause, but no, now the second time I found more things.

Now I have to figure out if I can power the unit outside of the car.



If we assume this is also correct for HU650 then I can apply power externally. Next is I wonder if I can receive FM signals with some unpowered wire I can use.

Then I can use the datasheet and hook my oscilloscope.

Note, that the unit is also implicated and I have witnessed it doing it, the unit turning itself on without pressing the power button, and also going from FM1 to FM2 or FM3 by itself. You cannot just say that the DSP SAA7709H is the one causing this, it just wouldn't make sense unless some feature is built-in for this to happen. However in my opinion, the power button does not actually turn off power to the entire unit, this would make it boot slower, it probably just turns off the LCD and some light sleep of the chips.

[vtl]

Time to upgrade to Kenwood!

I remember HU-650 were so cheap on ebay that I didn't even bother selling my 2 leftovers.

[dikidera]

Not ready yet to install a touchscreen. Plus I spent 30 dollars on a Bluetooth-FM dongle, I didn't manage to use it much.

I looked at the SAA7709H datasheet, but either it is incomplete or I am missing how the chip selects the input signal. It has what is called an "Analog Source Selector" which has no pin to control. So how does the chip select between signals?

Addendum:Must be this "Analog input selection via I2C bits ($0FFD) signal destination"

The SAA7709H datasheet is incomplete, what is missing is multiple chapters, especially Chapter 9. For this, we can find the full datasheet albeit for 7706H on here https://www.nxp.com/docs/en/data-sheet/SAA7706H.pdf . This describes that the input selection is done via I2C.

I don't claim to be an electrical engineer, but several things caught my eye.

From what I know about microcircuitry, each module in integrated circuits sometimes need their own power supply source, in this case the FSDAC module needs 3.3v. Missing or low voltage on any voltage rail will produce undefined behavior. Incidentally, I did find a single cap, 3.3v that had a cracked solder joint, but it was connected to ground, so more like power stability.
Power on mute - this is again a circuit that could be causing this, probably to avoid crackles and pops during power on/off.

From what I've read, the HU radios output some voltage to the antenna, missing voltage could cause the issue. As well as a broken antenna, of which there are two for multipath diversity(of which I know next to nothing).

[dikidera]

I want to ask if the +ANT output is supposed to be 10v or 11.7 like I had measured? Someone mentioned 10v but also mentioned any higher and the antenna amp will not work properly.

I do not know how this amp works, but after tracing the circuits I saw that there are two inputs so two antennas, which is correct. One is Y->1MOhm->[an array of smd components I cannot identify]->shielded box. I have seen these shielded boxes in old TVs so it's doing something. RF Tuner?

the other antenna signal goes like so

Y->1Mohm->capacitor->gnd. However the signal is also passed through a diode before the cap, which is likely 0.3 or .7 volts drop. This implies the signal voltage is at least higher than .7v if not the 10-12v supplied by +ANT, carrying the signal.

[FMradio]

I have a theory which is that there are some air vents behind the dash where the radio is and Volvo used the foam gaskets in them. There's a huge heater air box directly behind the radio with foam gaskets, that you can obviously see behind the radio, and even see that parts are missing or crumbling. And if you turn on the cabin air blower, you can feel a significant amount of air flowing behind the radio. (Either hot or cold, it is the same temperature as what your vents are blowing)

And as far as I know it's impossible to replace the foam in the heater air box behind the radio, without removing the entire dash, it's a horizontal rectangle shape, so the best I can personally do is remove the old foam (because it's disgusting) and tape the gap up with aluminum foil tape that's designed for HVAC.

Problem is the gasket extends behind the dash, where you can't easily get to it to apply tape to seal up leaks, but I guess taping as much as you can reach would minimize the air leak. And perhaps you can think of a creative insulation layer to block airflow from the dash to the radio.

They also use the foam at the vent outlets on the dash, But that's probably a much smaller air leak than the heater box's.

[dikidera]

Regardless, the issue that happens is permanent, there is damage, that may be fixable. My symptoms are, that as the radio gets hot, it starts working. Usually this does mean cracked solder joints, of which I found many on the radio. However everyone looks at the mainboard, but not the volume control + display board. And the antenna power supply or antennas.

A few other symptoms I noticed: Sometimes it cannot find any FM station, even with my dongle plugged in, this is clear indication the antennas are not picking up the signal, which is either the antennas or power supply to them, since they are powered antennas.
Sometimes my music works perfectly when it gets hot, until a certain region on the road where general reception of signals is bad and the radio simply stops working, even with the Bluetooth FM dongle. It has happened twice that my audio cuts out at that particular location.

What we need to know is how much voltage is output to the powered antennas with a working setup. Then we can measure what voltage is output from the non-working HU units. If the voltage is correct, we can determine if the power supply circuit works or not.
Next is volume control knobs circuit. I have determined that sometimes with very serious punches I would make it work for a long time.

In summary:
We have two antennas for multipath diversity. These should be checked for correct voltages to determine next step.
Volume control knob is a well overlooked aspect of the HU units. It uses potentiometers that may be dirty or with cracked joints.
The final culprit, the mainboard and it's DSP SAA7709. Maybe it has a loose bond inside. But some honda units also use the same DSP and those guys have never had complaints of a bad DSP.

[cmayo1]

Any updates to this? Don't feel like buying a new stereo and would rather put the man hours in (free time ≠ money)

[dikidera]

Unfortunately not. No matter what I tried I couldn't fix it and every attempt required reinstall to test. In the end I caved and got a used one.