across the bench [season-2] the electron strikes back

rivals - 5.jpg
this must have been an integrated amp chassis at the factory

rivals - 6.jpg
this particular preamp had an intermittent signal issue. i soldered 2 of the 8 connections for comparison, can you guess as to why there was an issue?

broken solder joints from the factory would be my guess due to the quick tack weld/soldering. there is no hardware (bolts/screws) holding this board to the chassis, just the solder connection to the chassis mount rca inputs.
 
8 twin triode tubes plus two rectifiers for a stereo preamp without a phono stage? That just seems excessive.

For reasons I don't fathom it seems like using way too many parts is the thing to do with import gear.

and A+ solder and mechanical work there.
 
rivals - 7.jpg
fully functional and reassembled. top vent vs tube locations should be noted

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no vents on bottom or sides, also noted (potential cooker)

rivals - 9.jpg
not too hungry after warmup, ~40w space heater equivalent
 
I saw 6N6 on the board near the two outboard rear tubes.
6N2 at the rear inboard
6DJ8 at both front positions

guessing the rectifiers are an EZ80 equivalent.
 
nad t753 - 8.jpg
nad t-753 multi channel receiver, power button doesnt work. if you push any of the other buttons it will wake up from standby though.

nad t753 - 9.jpg
more than a few things going on with the back panel


NAD T 753 A/V Receiver At A Glance & Ratings

At A Glance: NAD T 753 A/V Receiver Connections Inputs: Video: component video (2), S-video (5), composite video (5) Audio: coaxial digital (4), optical digital (2), 7.1-channel analog (1), stereo analog (7), preamp (6), AM/FM Outputs: Video: component video (1), S-video (3), composite video (3)...
www.soundandvision.com www.soundandvision.com
 
nad t753 - 10.jpg
a quick look top side, heat sink seems a bit short in terms of fin depth. wonder if there is active cooling.

nad t753 - 11.jpg
yup, nice array of fans that should keep the good times flowing (cfm style).
 
nad t753 - 1.jpg
it was interesting to see that pushing any of the buttons, except the power button, could wake the system from standby. although no way to turn off the system unless pulling the power cord. power button had zero effect, on or off.

nad t753 - 3.jpg
removing the power button board requires some face plate surgery, for complete module/board removal
 
nad t753 - 5.jpg
chopped the cable and cleaned up the board, fresh solder should be good to go

nad t753 - 6.jpg
fully re-installed, and now the power button works

nad t753 - 7.jpg
system idles high even when in stereo mode, more than a few circuits need to be fed regardless so this isnt a red flag concern.
 
aragon 8008 - 1.jpg
up next is an aragon 8008 power amp

aragon 8008 - 2.jpg
simple amount of inputs (no XLR option installed) and outputs vs the avr completed earlier


Aragon 8008 power amplifier Specifications | Stereophile.com

Sidebar 1: Specifications Description: Two-channel solid-state power amplifier. Rated power output: 200Wpc continuous into 8 ohms (23dBW), 400Wpc continuous into 4 ohms (23dBW). Rated full-power bandwidth: 5Hz-20kHz. S/N Ratio: >110dB, A-weighted. THD: 0.04%, 5Hz-20kHz, at full power into 8...
www.stereophile.com www.stereophile.com
*output: 8r=200w 4r=400w
 
aragon 8008 - 3.jpg
some ventilation although channel pcb's have different sized chambers and thermal reactivity

aragon 8008 - 4.jpg
looks like left channel will be a nightmare if it ever needs removal. like for a recap of repair or cleaning relay contacts...
 
aragon 8008 - 5.jpg
an interior view of the difficult to access channel

aragon 8008 - 6.jpg
the outside channel and its small compartment. looks like the board has space for more output transistors.
 
aragon 8008 - 7.jpg
closer look at power caps

aragon 8008 - 8.jpg
toroid transformer, jmp electronics 18-0700 rev. a

also a thermistor parked next to the txf.
 
aragon 8008 - 14.jpg
the results after a rather invasive cleaning. earlier measurement(s) were around 70r and randomly higher.

aragon 8008 - 15.jpg
left channel doesnt seem to have any issues

the dmm activity above can easily be done to evaluate output relay pass/fail status. no signal nor preamp nor audio nor speakers required. a simple sanity check.
 
aragon 8008 - 11.jpg
carefully opened the relay and removed its spring to access the contacts. lots of carbon, wonder how many high output disruptions occurred with this amp so far. typically a large arc happens when high current is flowing during the contact opening action.

aragon 8008 - 12.jpg
inspecting and need to clean both sides. note that the relay is still in the circuit board. removing the board from the chassis looks to be time consuming. cleaning the board mounted contacts would be a good idea as well.
 
gadget73 said:
while playing it would abuse the contacts.
Click to expand...
playing at "mine goes to eleven" and then the ac mains is interrupted or power button exercised would definitely cause some arc&spark activity. although regular low level output and then power off would be a significant yet gradual erosion of the contacts too.

amazing how an output safety relay can also be an eventual weak link in a system. electrolytics have some competition.
 
aragon 8008 - 13.jpg
one contact cleaned to compare with the others. obviously used deoxit pro-gold for final surface conditioning on all the contacts involved for this relay.

aragon 8008 - 16.jpg
top installed and ready for some exercise. thermals coming up soon, if people are into that type of engineering nerd candy.
 
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