AnyTone-D868UV
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geary
Audio far too quiet despite level 8 (AnyTone-D878)
There was a bang or loud blob when receiving DMR. Then the audio volume is only estimated at 20% maximum. The same with headphones. The maximum level (8) is set. Does anyone know of this error? Does anyone have a schematic? Best regards Frank
Hi Frank, I suspect a failure in the AF amp. It consists of a HM8872 Class AB / D audio amp. See http://hmsemi.com/downfile/HM8872.PDF for the datasheet with sample circuit. (Google translate will provide an english text version) The amp chip is placed next to the headphone plug on the rear PCB side. The circuit around seems to be pretty close to the application in the DS. As there are only ceramic Cs and some Rs around, my guess is one half of the HM8872 has been probably blown. You may check Digikey, Mouser or similar if they can provide spares. The chip's housing is SO8, with a bit skill you should be able to replace it.
Hallo Bert, vielen Dank für die Info. Damit hast Du mir schon mal sehr geholfen, den Fehler einzugrenzen. Das Wechseln sollte nicht das Problem sein. Leider konnte ich keinen Lieferanten finden. Auch nicht unter den von Dir genannten. Beste 73, Frank - DL8FX
I've got a radio here with the EXACT same problem. I'm also having trouble tracking down a replacement part, but if I can find anything I'll post back here.
If anyone else has any idea for a suitable alternate, I'd love to hear it!
With a bit of fiddling it should be possible to use a SSM2305 amplifier IC by Analog Devices. It is available in 8-pin MSOP case and fits directly onto the available print of the HM8872. As the specs of the SSM2305 are slightly different, some additional modifications to the circuit are required:
- remove the bypass cap connected to pin 2 as SSM2305 does not require an external bypass capacitor.
- Pin 3 mode pin is now In+, but already tied to gnd as required for single ended operation.
- Pin 1 will be the most difficult one: Unfortunately shutdown polarity of SSM2305 is inverse to the original HM8872. There seems to be an inverter stage with a single transistor close to pin 1 which can probably bypassed by removing the transistor and its collector resistor and placing a 0R resistor onto the free pads between collector and base.
Most critical point will be the supply voltage: The HM8872 is directly fed with 7,4V nom. from the battery. This is far too much for a SSM2305, its abs. max. voltage is 6V, recommended operating is 5V. On the top side of the PCB back to the HM8872, close to the GPS connector, there is a yellow tantal cap 33uF which provides decoupling for the audio amp. Next to it there is a ferrite bead connecting to 7,4V. This bead must be removed and soldered to the free pads left up its original position. It then connects to the 5V regulated rail which is fine for a SSM2305.
For replacing the audio amp chip, due to its exposed gnd pad on the bottom, I suggest to use a hot air SMT rework station. Earpiece connector close to the chip must be shielded against melting by a piece of aluminium foil.
BTW: Before stepping into above instructions first check the two ferrite beads at pin 5 and pin 8 for proper conductance! It could happen that one of them has degraded, so check if their resistance is somewhat around 1 ohm. Disconnected the display ribbon to prevent measurement affected by the speaker resistance.
Hello to all,
Where could I buy this HM8872 semiconductor, does anybody have any idea?
Thank and have a nice day! Savo
Where could I buy this HM8872 semiconductor, does anybody have any idea?
:-) If it were obtainable easily, I wouldn't have worked out a replacement solution like above.
For anyone else experiencing the quiet audio issue, actually test that amp chip before jumping to conclusions and doing a bunch of work to replace. In my case the amp ended up testing out fine, and it was the actual SPEAKER that had failed. Odd that the speaker failed to a state of quiet but perfectly clear, but that was my discovery. In that same vein, if anyone had a source for a proper replacement speaker that would be great. I have something in that is functional, but not rated to the same power as the stock speaker. The stock speaker is quite powerful for its size, and tough to find.
So before you spend the time replacing that amp ic, make sure it is really the culprit. :)
On Fri, Feb 5, 2021, 10:03 Bert, DD5XL [email protected] wrote:
Where could I buy this HM8872 semiconductor, does anybody have any idea?
:-) If it were obtainable easily, I wouldn't have worked out a replacement solution like above.
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Hi, In my case, the HM8872 is destroyed, so I need to replace it and audio is not working at all.
I haven't been able to locate a HM8872, but a LTK5130 seems to have the same pinout. One difference is that the HM8872 has a max Vdd of 8.5V where the LTK5130 has a max Vdd of 7.5v, so a bit less margin... Available through AliExpress. You will still need to bypass the inverter, as above. I may try inserting a SMD diode on the supply side for longevity's sake...
Hi Guys, I confirm adding successfully an LM4871M amplifier IC, need to modify VDD to 5V as above, and tie pin 2 and 3 toghether, also adding a gain setting resistor between pin 4 and 5 as in the datasheet. https://www.ti.com/product/LM4871/part-details/LM4871M/NOPB
also a note that the speaker in not connected via the display ribbon cable (at least in 878 Plus) but via two springs from the main PCB... contacting the speaker tiny PCB
