A-700 Restore

Start checking your power supply voltages.
On the power source 1 board (the one with the diode bridge) there is 45.5 vac from either red to black, should be power from transformer.
I’m measuring 117vdc across the red (B+) and blue (B-) seems high... not sure where to look on schematic to see what it’s supposed to be but I’m pretty sure it is power to the main board.
There is also on power source 1 board a
Black (E) and white (DSC) wire. I’m measuring 52.3vdc across those.

All measurements are taken while on DBT
 
Much better then what I’ve been using thanks, What am I looking for? I know your busy mr @avionic and don’t want you to stop what your working on. When you get a chance I could use some help if your up to it
 
Measure the collector voltage of each of your output transistors.( B+ and B-). Both Channels.
 
TR151 (relay driver) Need to know the emitter,collector and base vdc's
 
Me @avionic, I’ve got to get up early for work. I’ll be back online tomorrow evening if your available. I sure do appreciate your time and hopefully we can start where we left off tomorrow. Thank you
 
As an armchair observer vicariously playing along at home, I'm concerned for the amplifier's safety. :lurk:
TR 151
E .0
C 58
B .0

TR 152
E 0
C 58
B -3.6
Please verify your voltage measurements/supplied information.
According to the circuit diagram, TR151's Emitter CANNOT be at a different potential to TR152's Base. :no:
Yamaha_A-700_TR151andTR152.jpg

I suspect that you've swapped/muddled the transistor designations: i.e. TR151 voltages are actually TR152 voltages and vice versa. :dunno: :confused:
Bad news, after soldering all the caps and reorienting the bias transistor...

Rechecked orientation of ecb on bias transistor and it is correct.
A picture of the transistor orientation is worth a thousand words.

N.B. The assistance/answers you receive will, in most cases, be based on the information you supply. If you supply erroneous information, you'll destroy the amplifier. :blah:

And...
The DC voltage polarity indicators are NOT optional - please specify + or - with each DC voltage measurement. The DC voltages and their polarities should be measured with the black probe welded to the zero volt reference: i.e. the copper busbar or the black leads on the 22000uF capacitors. :blah:

The following misleading information indicates a fault as both B+ & B- are at the same (unspecified polarity) potential. :whip::eek:
B+ 58.8vdc
B- 58.8vdc
Both channels same
Another example
...I measured 36v dc on both hot sides of the relay contacts.
+ or -? :dunno:

As there's 36V of unknown polarity at the L & R relay contacts, it suggests that the problem is common to both channels.

With your meter's black/negative lead welded (not clipped) to the 0V reference point, please measure (at both individual component leads) the voltage and polarity at C205, C210, D149 & D150.
Please post the results.

N.B. You don't need to weld the negative lead to 0V - clipping is sufficient. :rflmao:
You must always use the bulb limiter (DBT) until ALL issues are resolved.

BEWARE - There are several errors/inconsistencies in the circuit diagram!

DO NOT assume that because you've replaced parts the issue is resolved. VERIFY!
200w_d.gif

DO NOT use/select the PHONO input until the current issue is resolved. :no:
DO NOT engage CLASS A until the current issue is resolved. :no:

DO Engage the SUBSONIC filter - it will block any DC voltages coming from the pre-amp stages.

Good Luck!
 
Thank you @Hamish119 for this post, one thing I have to do before I go any further is pick up a better set of leads for my fluke, I’m hoping to get that today if time permits after work. (Unlikely though as we are having a hospital power shutdown this evening). I know I need the electronics type leads with the sharp pointed end. I will review your post and follow up when I’m able to get back to work on it. Thanks again
 
Thank you @Hamish119 for this post, one thing I have to do before I go any further is pick up a better set of leads for my fluke, I’m hoping to get that today if time permits after work. (Unlikely though as we are having a hospital power shutdown this evening). I know I need the electronics type leads with the sharp pointed end. I will review your post and follow up when I’m able to get back to work on it. Thanks again

Are you doing a "pull the plug and see what happens" power test at the hospital? That's always stressful. We're doing ours next month. Good luck.

Cheers,
James
 
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