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  1. Mayank

    Happy Birthday Mayank!

    Thank you guys. I'm back home in DC after a long stint in rural/remote Tanzania where access to stable internet & cellphone was a challenge. Need to catch up on posts/messages and action at AK ;) Rgds Mayank
  2. Mayank

    AK is 19 years old, so we're having a raffle.

    June 20, 2004
  3. Mayank

    All amped up about another piece from Mayank!

    Awesome! You are welcome Scott. Do share your feedback after ~20 hours of settling in. The new capacitors in the signal path should make it sound even smoother. I have to visit you and listen to your amazing set up. Stay safe & healthy my friend Mayank
  4. Mayank

    Mid-Atlantic April Zoom Gathering 4-11-21

    Looking forward for tomorrow - I will be home after getting my second shot :thumbsup:
  5. Mayank

    Rotel RB-990BX 53V on the right speaker terminal!

    Sorry I am travelling - very unreliable internet here in Kigoma, Tanzania. Will reply when I get back home next week
  6. Mayank

    Carver TFM-6CB

    Awesome. Congratulation on a job well done! Nothing is more satisfying that seeing (hearing?) the success of your work!! A few suggestions: 1. Do check for DC offset on the outputs - you don't want to damage your PC-80's. Replacing the dried electrolytics is a good idea and will make the...
  7. Mayank

    Carver TFM-6CB

    :thumbsup: That was exactly my chain of thought too! By lifting one leg of D4 can confirm this if relay were to click. Wish Carver had incorporated a full wave rectification design here instead of saving pennies. Rgds
  8. Mayank

    Carver TFM-6CB

    @lifer70 - do not replace any new parts as yet. We need to get the relay working first. Good work testing D004. My chain of thought is slightly different. Please reinstall the relay and re-solder the legs of components lifted - all except one leg of D004. Check if the relay engages with D004 in...
  9. Mayank

    Carver TFM-6CB

    @lifer70: I went through my notes for a TFM-15cb which had a similar relay-not-clicking-on issue (both these amplifiers are very similar in design). Follow my chain of thought first before you replace Q4/and any other components - lift/desolder one leg of diode D004 and check if the relay comes...
  10. Mayank

    Carver TFM-6CB

    Carver was notorious to have typos in the service manuals/schematic - but they did issue several service bulletins correcting the errors. In the schematic that I have Q004 is 2SC2235 NPN 800mA 120V. I would expect you have narrowed the issue with the relay circuit to just these components...
  11. Mayank

    Adcom amplifiers

    Adcom GFA-555 (not the II) and the GFA-565 mono-blocks are by far the best sounding designs by Nelson Pass for the money. Adcom's later models did get some bad press, which was partly due to sub-standard components. Like several manufacturers of that era, Adcom was also unknowingly a victim of...
  12. Mayank

    What I learned on Craigslist

    Snip Snip :cool:
  13. Mayank

    Carver TFM-6CB

    We are all glad to help - AudioKarma is a great place! Do let us know if your amplifier works now. Remember to carefully bring it up with a DBT/variac. You may need to recalibrate bias and check for DC offset. Recapping would be a good idea. I had a TFM-6c on the bench a few months ago - it...
  14. Mayank

    Carver TFM-6CB

    P1. P3 show correct rail voltages and your emitter resistor readings are normal. To confirm if relay is bad (1) check for 12v at J005 (between blue & red cables) (2) with a DBT in place, connect an input signal (CD) and see if you get audio output at R004 (Right) & R005 (Left). If (1) and (2)...
  15. Mayank

    Carver TFM-6CB

    +1 Also, assuming the two 6A fuses F001/F002 are good, with power switch on what voltages are you getting at P1, P2, P3 for +B, gnd & -B respectively? Rgds Mayank
  16. Mayank

    Rotel RB-990BX 53V on the right speaker terminal!

    Ivo: I was waiting for you to get your amplifier working before recommending upgrades 1. A complete recap as there are only 5 electrolytic capacitors on each board (will dramatically improve the sound). 2. Installation of a speaker protection board. I have had great success with this one from...
  17. Mayank

    Rotel RB-990BX 53V on the right speaker terminal!

    1. Good that all the emitter resistors are OK. 2. Do a diode test on the balance 4 of 2SC3856 to confirm they are OK. 3. Check driver transistors Q635/Q633 (D1047 & B817) also mounted on the heat sink. They should not have a short on C-E. 4. If everything is good, you can re-solder the lifted...
  18. Mayank

    Rotel RB-990BX 53V on the right speaker terminal!

    Good progress Ivo. 1. No to eBay; it is full of counterfeit devices being sold. Always buy from trusted sources. Digikey is the authorized retailer for Sanken. C3856ND will work. Don't be in a hurry to place the order, there could be more components you may need to replace. 2. I usually change...
  19. Mayank

    Rotel RB-990BX 53V on the right speaker terminal!

    Here is the complete schematic on one large page :) Edit: Hmmm I wonder why it didn't upload in the full size
  20. Mayank

    Rotel RB-990BX 53V on the right speaker terminal!

    Also ivo, C624 is in the RIGHT channel which is good :cool:
  21. Mayank

    Rotel RB-990BX 53V on the right speaker terminal!

    ivo: In your post #5 you have confirmed all the NPN output are showing a dead short on C & E. This means one or more of the 2SC3856 transistors have a fault. As all 5 have their C's connected, all will show a short even if one/more is bad. Recommend you desolder and lift just the middle C leg...
  22. Mayank

    Rotel RB-990BX 53V on the right speaker terminal!

    Hi ivo: Please confirm you checked for short between Collector & Emitter (pins 2 & 3) of the 2SC3856 transistors. The pictures shows diode test between B & E (pins 1 and 3) . Rgds Mayank
  23. Mayank

    Rotel RB-990BX 53V on the right speaker terminal!

    Dear Ivo: The RB-990BX is a very respectable amplifier from the "990 series" which was the last of their top of the line ones made in Japan. With both line fuses out on the LEFT channel and 57V on the speaker terminals means there is a significant fault - probably due to one/more of the output...
  24. Mayank

    Relay replacement: JC2aD DC48V

    Good luck. FYI the one I bought on AliExpress/Alibaba was made in Indonesia and cost ~$6 + shipping. There were a few other vendors selling similar ones for 1/3rd the cost. I decided to go with this - you get what you pay for. The relay has been working as designed over the past two years.
  25. Mayank

    Relay replacement: JC2aD DC48V

    From this vendor I had ordered a different DPDT 10A DC48V relay LY2-DC48 - it was well made and a perfect fit Rgds
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