NAD 3155 outputs one channel only

[fiskmaas]

I'm getting good signal on both of these points with oscilloscope. Shouldn't that point to the relay as the issue here?
Left most:
Right most:
1khz tone


Edit: dammit, managed to bridge the two jumpers to the right (red cross and just right of red cross)... the relay is now off all the time and the protection light on the front is completely off, even from powering it on... I assume the relay is fried so I ordered a new one. Let's hope it fixes it.

 

[mbz]

Edit: dammit, managed to bridge the two jumpers to the right (red cross and just right of red cross)... the relay is now off all the time and the protection light on the front is completely off, even from powering it on... I assume the relay is fried so I ordered a new one. Let's hope it fixes it.

The jumpers are the outputs from the L&R power amps, you've probably damaged(shorted) output transistors, the relay should
be ok. Suggest measure dc voltage at each jumper to GND, expect less than 100mV, you will probably have 20-40Vdc

 

[fiskmaas]

The jumpers are the outputs from the L&R power amps, you've probably damaged(shorted) output transistors, the relay should
be ok. Suggest measure dc voltage at each jumper to GND, expect less than 100mV, you will probably have 20-40Vdc

Oh, allright. Measurements: -37mv, -59mv and 1.1v

 

[mbz]

Power amp outputs look fine (37mV, 59mV) so no short. The 1.1V link is for the relay power (24V?). Check R801 (FR, 33ohms)
and Q801 for a c-e short.

 

[fiskmaas]

Power amp outputs look fine (37mV, 59mV) so no short. The 1.1V link is for the relay power (24V?). Check R801 (FR, 33ohms)
and Q801 for a c-e short.

R801 = 160 kohm rising
Q801 not entirely sure how to check that, if it's just continuity to ground there is none.

 

[mbz]

R801 = 160 kohm rising

Not OK, should be 33 ohms, replace with 279-FRN25J33R ie, fusible, flameproof, ok to replace
with ordinary metal film for test pruposes.

Q801 not entirely sure how to check that, if it's just continuity to ground there is none.

Preferred to use diode test function on multimeter, however resistance check between emitter and collector would also
work. Something for your toolbox, a nice graphic from markthefixer, red/black indicate meter probe orientation. 2 results
expected either 650mV (550-750mV) or OL (Open Loop/Circuit)

 

[fiskmaas]

Not OK, should be 33 ohms, replace with 279-FRN25J33R ie, fusible, flameproof, ok to replace
with ordinary metal film for test pruposes.

Preferred to use diode test function on multimeter, however resistance check between emitter and collector would also
work. Something for your toolbox, a nice graphic from markthefixer, red/black indicate meter probe orientation. 2 results
expected either 650mV (550-750mV) or OL (Open Loop/Circuit)

Ok, I'm getting 1.6-1.8V here...

I'll have to order new resistors for R801.

Also, I replaced the R907 with a ceramic wire wound one before, should I get a different one for that as well or is that ok?

 

[mbz]

Certainly R801 is faulty, replacement may fix all, however the excess current through R801 has probably done downstream (Q801)
damage.

Also, I replaced the R907 with a ceramic wire wound one before, should I get a different one for that as well or is that ok?

A Mouser search only came up with
KNP500JT-91-220R

I would have liked a low noise metal film, even flameproof, something like the cpf series? Looks like you are stuck with
the wire wound, needed to dissapate the 5W.

 

[fiskmaas]

I'm having trouble finding any reference to low noise or flameproof on the resistors I'm looking at:
https://asset.conrad.com/media10/ad...ohm-axial-hallmonterade-0207-025-w-1-1-st.pdf
https://www.switchelectronics.co.uk/33r-metal-film-0-25w-resistor-1
https://www.elfa.se/en/carbon-film-...&pos=1&origPos=252&origPageSize=10&track=true

I've ordered some regular carbon/metal film ones, will have to do for now.

As for the Q801, I'm not entirely sure what to look for. Would this do for example?
https://www.electrokit.com/en/product/kta1023y-to-92/

 

[mbz]

Fusible resistors in the wanted size,ratings are harder to find.
Often need to go for metal film, though would be wise to include
flameproof/flame retardent. Suppliers is also an issue, assume
mouser/digikey are delivery cost prohibitive in which case go with
the linked item.


Regarding Q801, with amp powered off/unplugged "measure" resistance
between the collector and emitter, easiest to measure between items
marked below. A near short indicates failure. Q801 2SA988, simple
switching purposes. KSA992 looks like an ok match.

 

[fiskmaas]

Fusible resistors in the wanted size,ratings are harder to find.
Often need to go for metal film, though would be wise to include
flameproof/flame retardent. Suppliers is also an issue, assume
mouser/digikey are delivery cost prohibitive in which case go with
the linked item.


Regarding Q801, with amp powered off/unplugged "measure" resistance
between the collector and emitter, easiest to measure between items
marked below. A near short indicates failure. Q801 2SA988, simple
switching purposes. KSA992 looks like an ok match.
View attachment 1985644

Measured 106 kohm between the points.

Ok I'll see if I can find KSA992 here, mouser seem to be the only ones who carry it. Is ebay a bad source?

 

[mbz]

106kohms is not a c-e short so I'd go with replaceing faulty R801 only.
ebay is a bad source, mostly fake parts from china

 

[fiskmaas]

106kohms is not a c-e short so I'd go with replaceing faulty R801 only.
ebay is a bad source, mostly fake parts from china

Allright, replaced R801. Relay is functioning properly now. Awesome.
Sound is as usual though, no left channel.

 

[mbz]

Back to original problem, good.
Real busy at moment, will try and find time later in night

 

[fiskmaas]

Back to original problem, good.
Real busy at moment, will try and find time later in night

No rush mate, appreciate you taking the time.

 

[mbz]

Could you try oscilloscope trace at left speakers post with spkr also connected, thinking that the channel falls over
when loaded by the speaker. Previously you had 1kHz signal at left spkr post (no spkrs connected)

 

[fiskmaas]

Could you try oscilloscope trace at left speakers post with spkr also connected, thinking that the channel falls over
when loaded by the speaker. Previously you had 1kHz signal at left spkr post (no spkrs connected)

Right:
Left:
Note the difference in voltage range. 1khz tone. ~same volume
Signal is there and changes with volume, but is substantially lower than right and not audible. Measured with speaker connected on both.

 

[mbz]

Waveforms at post#61 (relay input, no spkrs connected) look about the same.
Post #47 don't look great but should be audable at 0.5V/div

With spkrs connected, check trace at jumpers as per post#61. Ccompare
with trace at white wire, if this trace is attenuated compared to #61
then blame relay contacts, replace relay.

 

[fiskmaas]

Pre relay jumpers look good.
Post relay output looks the same as speaker posts (#77).
Relay confirmed then, awesome.

I'm looking at these for replacement, 24V 2A
TR5V-M-24VDC-S-Z
HR93-DC24H
Should work right?

Edit: Looked at some other threads and G5V-2 with some modification seems the best replacement available.

 

[Stepwise]

I used Omron G2R-2A-DC24 that were a drop in replacement relay in a NAD3400.
Check what the ratings are for the original relays, I have no idea of what model number
they have. (DigiKey # Z3132-ND for the ones I used)