I have a 4-year old HK3490 that randomly goes into protect mode. When this occurs, the display reads "Voltage Protect Check DSP". The only info I've been able to find on the internet is "send back to Harmon Kardon for repair".
I have checked all the speaker connections and etc and found no issues. If I unplug the unit for several days and reconnect to AC power it will sometimes run for days without going into protect mode.
For these types of integrated receivers, is there any hope of a DIY'er, with electronics background, repairing this type of problem? Where to find a schematic or troubleshooting guide? I really like the unit, but could probably buy something else for what it would cost to send to HK for repair.
I have checked all the speaker connections and etc and found no issues. If I unplug the unit for several days and reconnect to AC power it will sometimes run for days without going into protect mode.
For these types of integrated receivers, is there any hope of a DIY'er, with electronics background, repairing this type of problem? Where to find a schematic or troubleshooting guide? I really like the unit, but could probably buy something else for what it would cost to send to HK for repair.
Found a service manual (SM) with schematic online.
There is a reset procedure in the SM that I tried. Still going to Protect mode thereafter.
Sometimes it seems the receiver runs longer without going into "protect mode" if I reseat the ribbon cables. Perhaps the reseating is "fixing" a bad connection on the PCB, for a short time? Sooner or later I end up back in Protect mode. I've been running the receiver with the top cover off for a while.
From the schematic, it appears that each "Protect" signal is derived from the DC power supply voltages for that circuit section. Each DC voltage is applied across a resistor divider, then the mid points of all the dividers are wire-ANDed and clamped with a zener to become the "Protect" signal. Going to check the PS voltages tonight.
There is a reset procedure in the SM that I tried. Still going to Protect mode thereafter.
Sometimes it seems the receiver runs longer without going into "protect mode" if I reseat the ribbon cables. Perhaps the reseating is "fixing" a bad connection on the PCB, for a short time? Sooner or later I end up back in Protect mode. I've been running the receiver with the top cover off for a while.
From the schematic, it appears that each "Protect" signal is derived from the DC power supply voltages for that circuit section. Each DC voltage is applied across a resistor divider, then the mid points of all the dividers are wire-ANDed and clamped with a zener to become the "Protect" signal. Going to check the PS voltages tonight.
Most of those protection circuits are triggered when there is DC offset voltage on the speaker outputs of the power amplifier.
Ideally there only should be the AC voltage audio signal on these outputs. A significant amount of DC voltage indicates a device is failing in the amplifier and throwing it out of DC balance.
The bad device could be in the power supply, but usually it is one of the output power transistors failing when it warms up.
Ideally there only should be the AC voltage audio signal on these outputs. A significant amount of DC voltage indicates a device is failing in the amplifier and throwing it out of DC balance.
The bad device could be in the power supply, but usually it is one of the output power transistors failing when it warms up.
Hi,
the thread is a bit old but I´ve got a HK3490 on repair from a friend which shows the same problem. Turn on...protect mode......turn off.
Sometimes the message "check input voltage" appears.
There seem to be more Harmans with the same problem so maybe it´s a standard failure? Would save me a lot of time searching if anybody knows a solution.
Thanks,
William
the thread is a bit old but I´ve got a HK3490 on repair from a friend which shows the same problem. Turn on...protect mode......turn off.
Sometimes the message "check input voltage" appears.
There seem to be more Harmans with the same problem so maybe it´s a standard failure? Would save me a lot of time searching if anybody knows a solution.
Thanks,
William
Looks like this is a standard problem on these. There is a check on supply voltages into IC51, its quite accessible. In my case +15V was gone. LM7815 was defect. I suspect this 15V might be the prime suspect. Unfortunately, this is on the bottom board, take off all other boards, then the ±15V is the regulators with quite large heatsinks.
Top tip: I grinded a hole in bottom plate, big enough for the soldering iron. This saves a lot of work, taking out bottom PCB is not a quick job.
Top tip: I grinded a hole in bottom plate, big enough for the soldering iron. This saves a lot of work, taking out bottom PCB is not a quick job.
Attachments
Also, Check the .47 ohm fusible resistors located right on the transformer PCB.
If you've lost the 15v supply, check the resistor supplying the 19v AC line.
If you've lost the 15v supply, check the resistor supplying the 19v AC line.
@Scanlines:
Will a fusible resistor show an infinite resistance (value of 1) if blown?
Both of my 19V supply's are reading 0V, and both 19V .47ohm fuses are reading 1 for resistance values.
Will a fusible resistor show an infinite resistance (value of 1) if blown?
Both of my 19V supply's are reading 0V, and both 19V .47ohm fuses are reading 1 for resistance values.
@Scanlines,
-------UPDATE--------
Bypassing these two resistors has SOLVED the problem!
(For anyone wondering, these are the lower two grey resisters on the TRANSFORMER board. #'s R951 & R952)
My Harmon Kardon 3490 no longer displays the "voltage check" error, and it no longer goes into protection mode!
I am ordering two replacement resistors, and will limit my usage until they arrive.
Cheers!
-------UPDATE--------
Bypassing these two resistors has SOLVED the problem!
(For anyone wondering, these are the lower two grey resisters on the TRANSFORMER board. #'s R951 & R952)
My Harmon Kardon 3490 no longer displays the "voltage check" error, and it no longer goes into protection mode!
I am ordering two replacement resistors, and will limit my usage until they arrive.
Cheers!
@Scanlines,
-------UPDATE #2--------
I AM able to get sound out of the amp, but ONLY when using the MAIN IN connection on the Main Board.
The amp DOES stay on, but none of the standard inputs work.
Any idea where to start?
- C
-------UPDATE #2--------
I AM able to get sound out of the amp, but ONLY when using the MAIN IN connection on the Main Board.
The amp DOES stay on, but none of the standard inputs work.
Any idea where to start?
- C
Hope DeepBlue555 got the amp working?
I have also fixed one by replacing the .47ohm fusible resistors.
A problem that remained was a pop in the left channel when powering off, changing input OR setting volume to -80dB.
So some mute circuit probably has failed.
That would be on the lowest down "main" board, right?
If someone knows what exactly could be the problem I would be delighted to know.
But I am hesitating to disassemble a 299 amplifier into atoms just to have a chance of finding the problem 🙂
I have also fixed one by replacing the .47ohm fusible resistors.
A problem that remained was a pop in the left channel when powering off, changing input OR setting volume to -80dB.
So some mute circuit probably has failed.
That would be on the lowest down "main" board, right?
If someone knows what exactly could be the problem I would be delighted to know.
But I am hesitating to disassemble a 299 amplifier into atoms just to have a chance of finding the problem 🙂
I hate receivers that does not have a removable plate at the bottom to avoid disassemble the whole unit to desolder a transistor,,,,grrrr
I am repairing one with DC at both channels, DC is around -6v but curiosly if I put a 12k resistor in parallel to a 33k R303 the dc offset goes down and I can hear music without overheating my speakers with the DC
I am repairing one with DC at both channels, DC is around -6v but curiously if I put a 12k resistor in parallel to a 33k R303 the dc offset goes down and I can hear music without overheating my speakers with the DC.
I am suspecting on Q301 to Q306, what do you think guys?
I am suspecting on Q301 to Q306, what do you think guys?
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I have just repaired this gem, sounds excellent for a receiver, this is because it uses discrete Bass, Treble and Balance...this avoid electronic ugly sound found on all modern receivers that use DSP which deteriorate significantly the sound.
I change all small transistors from Q301 to Q311 and its working fine now
I change all small transistors from Q301 to Q311 and its working fine now
Bonjour
après avoir vérifié toutes les tensions d’alimentions , supprimé les transistors de puissance.
La tension sur la zener 4.3V de sécurité reste 0.6 V
Le +15 & -15 sont bien présent
le +8 & -8 aussi
aucune ronflette sur ses alimentations. Petite différence de 0.1 à 0.2 v pas significatif
si j’alimente la détection DSP sécurité en 4.8 v, je me retrouve avec un autre code erreur
Check input et ainsi de suite.
Je pense à un pbl de l’IC 51 ? avez-vous ou ce problème ?
Cdlt
après avoir vérifié toutes les tensions d’alimentions , supprimé les transistors de puissance.
La tension sur la zener 4.3V de sécurité reste 0.6 V
Le +15 & -15 sont bien présent
le +8 & -8 aussi
aucune ronflette sur ses alimentations. Petite différence de 0.1 à 0.2 v pas significatif
si j’alimente la détection DSP sécurité en 4.8 v, je me retrouve avec un autre code erreur
Check input et ainsi de suite.
Je pense à un pbl de l’IC 51 ? avez-vous ou ce problème ?
Cdlt
