I have recapped a Nakamichi SR4A- sorted out the power supply, switch noises, some dead caps and even had it playing beautifully for a few hours.
I then started to reassemble it (bottom plate then top cover) and now it wont come out of protection- so I have disassembled, read all the previous posts here (and on AK), checked resoldered any dodgy looking connections and even found a broken wire....and yet still in protection.
I know the speaker relays work (they clicked beautifully before the reassembly), so now I am flumoxed.
The protection circuit components all measure correctly, and IC901 which is the protection IC has the following:
Pin1 -0v
pin2 0.14v
pin3 0v
Pin4 1.9v- not this comes form CN27- pin 1is 45v and pin 2-connected to pin4 on the IC is 1.9v
Pin5 0v
Pin 6 44v
Pin 7 0,05v
Pin 8 3.43v
The IC is a UPC1237h- which is apparently a common protection IC.
additionally the speaker relays are controlled by the speaker switches- which switch the 45v rail on pin 1 of CN 26 and return via speaker switch A to pin2 and speaker switch B to 3.these then go via 2w 1k resistors to the coil of the relay.
With either switch A or B in the off position there is 41v at pins 2 and 3, when switched in this rises to 45v- this seems wrong to me
CN17 pin 2 has 30v which goes to thermistor-and then connects to pin 5 (0v).
However I am very confused as everything worked great until the reassembly- which has made me double check all the connections and where the screws go etc.
I have attached the relevant part of the circuit
Any guidance on how to debug this would be greatly appreciated
I then started to reassemble it (bottom plate then top cover) and now it wont come out of protection- so I have disassembled, read all the previous posts here (and on AK), checked resoldered any dodgy looking connections and even found a broken wire....and yet still in protection.
I know the speaker relays work (they clicked beautifully before the reassembly), so now I am flumoxed.
The protection circuit components all measure correctly, and IC901 which is the protection IC has the following:
Pin1 -0v
pin2 0.14v
pin3 0v
Pin4 1.9v- not this comes form CN27- pin 1is 45v and pin 2-connected to pin4 on the IC is 1.9v
Pin5 0v
Pin 6 44v
Pin 7 0,05v
Pin 8 3.43v
The IC is a UPC1237h- which is apparently a common protection IC.
additionally the speaker relays are controlled by the speaker switches- which switch the 45v rail on pin 1 of CN 26 and return via speaker switch A to pin2 and speaker switch B to 3.these then go via 2w 1k resistors to the coil of the relay.
With either switch A or B in the off position there is 41v at pins 2 and 3, when switched in this rises to 45v- this seems wrong to me
CN17 pin 2 has 30v which goes to thermistor-and then connects to pin 5 (0v).
However I am very confused as everything worked great until the reassembly- which has made me double check all the connections and where the screws go etc.
I have attached the relevant part of the circuit
Any guidance on how to debug this would be greatly appreciated
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I downloaded the spec and application note for the UPC1237 ans from what I can see the voltages are all OK, except for pin1which measures 0.004v, and the spec sheet gives a range of 0.58 to 0.76, and pin 4 which is 1.9v, whereas the spec sheet gives a range of 0.6 to 0.9.
Both these ranges refer to inverting pin 6. Here is the link for the UPC1237:
http://www.unisonic.com.tw/datasheet/UPC1237.pdf
I have tested Q718 which is OK as are R903, R904, R902 and all the caps are new and working.
The pin 4 voltage comes directly from the PS (via CN27) and is AC taken before the bridge rectifier via R420 and D416. The bridge rectifier provides +/- 44v which is OK.
I am thoroughly confused and would be grateful for any hints or assistance
Peter
Both these ranges refer to inverting pin 6. Here is the link for the UPC1237:
http://www.unisonic.com.tw/datasheet/UPC1237.pdf
I have tested Q718 which is OK as are R903, R904, R902 and all the caps are new and working.
The pin 4 voltage comes directly from the PS (via CN27) and is AC taken before the bridge rectifier via R420 and D416. The bridge rectifier provides +/- 44v which is OK.
I am thoroughly confused and would be grateful for any hints or assistance
Peter
so further investigation has shown that if I remove CN17, which connects the logic board to the protection circuit- the flashing green light becomes solid, suggesting the protection circuit is operating correctly. The voltage on CN17 for the mute switch changes from 0v to 4.56v as i would expect. However the "power mute" voltage stays at 26v- which seems high as an input to the logic chip (pin22). The other issue that is causing me to worry is the speaker selector switch- which has 44v when selected and 41v when not selected- which seems very wrong to me- thus the relays are always powered, which I think they should not be for normal operation? again any help, guidance or advice welcomed, this one really has me confused Thanks Peter
Is the protection system faulty ?
Or.
Is the protection system doing its job because there's (now) a fault in the amp ?
Have a look at the audio signal before the output relay.
Or.
Is the protection system doing its job because there's (now) a fault in the amp ?
Have a look at the audio signal before the output relay.
thanks for the response
Yes audio on both channels is at the relays. So I think it is the protection.
and when I remove CN17, the green light goes form blinking (in protection) to solid- which suggests the protection circuit is working, however with no relay clicking in.
this one has me very confused
Yes audio on both channels is at the relays. So I think it is the protection.
and when I remove CN17, the green light goes form blinking (in protection) to solid- which suggests the protection circuit is working, however with no relay clicking in.
this one has me very confused
Does the audio at the relays have any DC offset though? If so the protection should be operating to save the speakers.