[Jonatan Sutrisna]

Yep, the channel boards. I ordered some replacements (slightly higher uF, but same dimensions) and I'll change them when they come in, 5 minute job to do those.

Here are the caps installed before I started closing things up. Nothing really exciting... but perhaps all these photos will help someone down the road.











As expected, the closing up the case work was the biggest part of the job. I'm glad I remove it, it made the solder work easy and I got a good look at everything to make sure it's all clean and looking good. Overall pretty easy job since the caps that spaceace picked were an easy fit everywhere.

Fired up, allowed everything to get up to temperature and settle, set DC offset and balance, and now playing some music.

It's always amazing how much better things sounds after we work on them? The 717 is really sounding wonderful tonight!!

Halo Shipsupt. My SRM717 sound is very weak despite the vol knob on maximum. Apparently R60/61, 63/64 & other power resistors' values mostly have changed. I believe its transistors' values also have changed. How did you adjust the DC offset ?

 

[BillyTea]

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.

Hello fellow Melbournian!

I believe those carbon composition resistors R60/R61 are more likely 0.5 W, just based on their approx. size and what I've seen before for that type of resistor. But I would probably replace it with a 1 W anyway! I like to use Vishay's Pro series resistors to replace any carbon composition resistors in power supply sections, they have options of 1, 2 and 3 Watts.
Interestingly it seems like you cannot buy the typical carbon carbon composition that easily anymore! Just had a look on Mouser and RS Components, my usual go-to's.

I'm also interested in getting my hands on the service document/schematic for the SRM-717 if someone can provide it?

Or at least hoping someone can provide some insights into what each of the trimpots are for? (TVR1 and TVR2)
And also recommended testing points as needed.
I keep reading people mentioning DC Offset (or "near zero") and Levels. To me this sounds like it's just the DC offset (to remove/minimise any DC on the output) and fine adjustment of the output volume level so that the Left and Right side can be fine tuned to match output levels?
There doesn't appear to be an actual Bias adjustment as such? Would love to hear more insights on this from someone!


I think likely that the two removable boards are the the amplifier boards, but the main output drivers are fed by these boards and are located on the big heatsink in the middle? I haven't tried to trace that far yet to see where things go.

Cheers!

 

[Jonatan Sutrisna]

Hello fellow Melbournian!

I believe those carbon composition resistors R60/R61 are more likely 0.5 W, just based on their approx. size and what I've seen before for that type of resistor. But I would probably replace it with a 1 W anyway! I like to use Vishay's Pro series resistors to replace any carbon composition resistors in power supply sections, they have options of 1, 2 and 3 Watts.
Interestingly it seems like you cannot buy the typical carbon carbon composition that easily anymore! Just had a look on Mouser and RS Components, my usual go-to's.

I'm also interested in getting my hands on the service document/schematic for the SRM-717 if someone can provide it?

Or at least hoping someone can provide some insights into what each of the trimpots are for? (TVR1 and TVR2)
And also recommended testing points as needed.
I keep reading people mentioning DC Offset (or "near zero") and Levels. To me this sounds like it's just the DC offset (to remove/minimise any DC on the output) and fine adjustment of the output volume level so that the Left and Right side can be fine tuned to match output levels?
There doesn't appear to be an actual Bias adjustment as such? Would love to hear more insights on this from someone!


I think likely that the two removable boards are the the amplifier boards, but the main output drivers are fed by these boards and are located on the big heatsink in the middle? I haven't tried to trace that far yet to see where things go.

Cheers!

Hi Billy. I think the tvr1 & 2 are to trimp the DC output. I put my DC voltage multimeter. The red I put on the output (if we facing the pcb from the bottom, they're on the left side. If I'm not mistaken there are 4 points with colour cables) & black to the ground. Before I move the tvr I marked it with marker pen its original position then I moved it a bit to left & right. I saw the V changed. I've already changed all the power resistors. Some changed alot. Result: the sound a bit better but still weak. I suspect one/ some transistors on the heatsink could be broken. I've got all the transistors for replacement but due to my other activities, I haven't got time to check it one by one. Need to check its parameters, eg. hfe, r value & whether its diodes leaking or not. I've bought Peak Electronic DCA 55 T.

I couldn't find its schematic on internet but similar construction can be found on Blue Hawai solid state energiser on its web. https://headwizememorial.wordpress....tatic-amplifier-for-stax-omega-ii-headphones/
Let me know.