SRM-717 Re-Cap
Aug 5, 2013 at 8:05 AM Post #31 of 46
This  is very interesting I like a challenge . I tested mine and both tested okay at 4.7M ohm, By removing the fuses you can test better in circuit. I agree the current shouldnt have affected them . But I have seen switch on surge take out resistors  Most of the resistors   I have come across especially in radio front ends go high. Those two resistors seem to be the only kind of that type[unless somebody has better eyesight  than me]  with capped ends. Studies of different types of caps on resistors were carried out in the UK in EW mag using special micro-ohm equipment and some were found to have a small increase in resistance over a period . The longer the higher the resistance especially high voltages employed .So the type of metal that is used for the caps[at each end] plays a part in the reliability of the resistor . I dont have the actual mag to hand but I have a good memory.It could be a combination of things that bring it about. I take it they are 500V types?
 
Aug 5, 2013 at 12:29 PM Post #33 of 46
Sorry to disagree but in my 717---R60/R61 are 4.7 MEG.Maybe if I give you the serial no. of the mother board it will help=PB-101/08454-0010. If your board shows different  . Then--- 1-UK and US boards are different??[not counting different mains voltage--or 2-modifications that Stax hasnt mentioned have taken place and circuit diagrams dont specify--seen this happen elsewhere--only government  equipment seems to show all mods.There is a 727-11 diagram on this website saying its a 727-11 diagram with a switch added for local/global feedback -.Some of the components numbered dont comply to my 727-11 also no input components are shown [small value caps for filter/bandwidth limiting purposes.] Whats going on Kevin?? I might be a subjective but when it comes to science and circuit design I am an objective. and can only see what a circuit board shows me. ----May I add found R63/R64 they are at the front of my board look like carbon types but they too are yellow/violet/green=4.7M ohm.
 
Aug 5, 2013 at 12:50 PM Post #35 of 46
Apart from the "pb" being in capitals ---yes Kevin. Can I also say that it-the 717 and the 727-11 were both bought from the one and only[as far as I know] authorized Stax dealer in the UK namely=Symmetry-quote-Authorized Distributor in United Kingdom-end quote.
 
Aug 5, 2013 at 1:10 PM Post #36 of 46
Make it four times; it was the same resistors giving me the intermittent fault.  
 
60/61
 
Quote:
its always the last thing you do that fixes the problem.
 
no reason those resistors should burn up, they are running at half power.
I think this is the third time I have seen problems with those 2 resistors.
And its always both of them.

 
Aug 5, 2013 at 1:37 PM Post #37 of 46
Shipsupt-That makes sense to me --attached-one end to each HV fuse. We both live in the UK maybe the US has mods to their -717. But thats not very good technical business as applied to Stax.  Making different versions [apart from mains supply] causes confusion and would mean their standard circuit  diagrams dont apply.   
 
Sep 24, 2014 at 7:51 PM Post #38 of 46
Hi guys,
I know this is an old thread but I am entering the world of Electrostatics and am looking at the 717 for my solution.....
 
I have always loved playing with electronics and am confident to solder, replace resistors, caps etc but I really have no idea regarding how to test and measure circuits.
 
My question is can the 717 be easily converted from 110 to 240V?  Would it require a new transformer? I note the caps are 400V so does that mean the circuitry would be fine with the change?
 
I would also like to thank you all for this thread... As I said before I love to tinker and could see myself trying to perform the mods as described in this thread in the future .......
 
Thanks
 
Jul 26, 2023 at 7:14 AM Post #42 of 46
The small ones in front of the mains transformer beside -IC -1 and IC-2 Are smoothing caps for those 2 +/- 15 V regulators in my conversion of the 727[ which is the same as 717 in this] I separated those regulators cut the PCB copper strips and added 2 more regulators so that BOTH channels had their OWN regulators thus stopping overhearing interaction between them causing a degradation of the stereo image.
I increased the values and also added more at the sockets of both channels- It has been proved scientifically that over a few
inches of track can pick up radiated or induced noise/distortion .therebye affecting the quality of the reproduced signal.
See my longer posts on the 717/727 elsewhere.
 
Last edited:
Jul 26, 2023 at 7:30 AM Post #43 of 46
Hi Duncan. I agree with you. I assembled Borberly headphone amp as dual mono. I was shocked about the air/ soundstage. At the beginning I thought why the sound became strange. Later on I realised that's the good effect of dual mono. Yes, it's hurting wallet as the price of the 2 PSU is more expensive than the 2 amps (stereo) itself.

About the IC regulators (7815 & 7915) on SRM717 where are the amps ? I think the 2 cards since they receive the input lines but there are 2 x 10 uF/ 400 V on each card. So, the amp is running on high voltage?
 
Jul 26, 2023 at 7:36 AM Post #44 of 46
CAPVoltageUFHightDiameter Note
C31251011.56.5Not much room for increased size
C32251011.56.5Not much room for increased size
C33251011.56.5Not much room for increased size
C34251011.56.5Not much room for increased size
C353547105 Lots of room for hight, 1.5mm extra for diameter
C363547105 Lots of room for hight, 1.5mm extra for diameter
C393547105 Lots of room for hight, 1.5mm extra for diameter
C263547105 Lots of room for hight, 1.5mm extra for diameter
C273547105 Lots of room for hight, 1.5mm extra for diameter
C22354701510 Not much extra diameter but lots of room for extra hight
C23354701510 Not much extra diameter but lots of room for extra hight
C24354701510 Not much extra diameter but lots of room for extra hight
C25354701510 Not much extra diameter but lots of room for extra hight
C184002204625No room for extra diameter but caps could be 60mm high
C194002204625No room for extra diameter but caps could be 60mm high
C204002204625No room for extra diameter but caps could be 60mm high
C214002004625No room for extra diameter but caps could be 60mm high
C11 #140010201030mmHighx16mmDiameter would be easy.
C12 #140010201030mmHighx16mmDiameter would be easy.
C11 #240010201030mmHighx16mmDiameter would be easy.
C12 #240010201030mmHighx16mmDiameter would be easy.

























Halo Spaceace. Are the sound cards the amps ? I think it's running on high V because there are high V caps (10 uF/ 400 V) on each card. What unit for (& where) of the ICs regulator?
 
Jul 26, 2023 at 8:05 AM Post #45 of 46
R60/61 are 1M resistors

R63/64 are 4.7M resistors
R60/61 4.7 M (likely 1 W) & R63/64 same 4.7 M (likely 1/4 W). Recently my Stax (headphones 4070 & SRM 717) don't wanna play. Despite the vol control maximum, I only heard small music & distorted. Whn I pulled it out & test R60/61 apparently the value becomes 8 M & 6 M. R63/64, 40/41, 42/43 & some other 1 W resistors' values also changed. I suspect the all power resistors. Well.... maube all the transistors' (especially the power transistors) values have changed too. I believe it's due to high temperature. I also in the process of replacing all of its electrolytics. When finish & back sounding again, I'll take off it's cover so the heat will not affecting other components.
 

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