Re: Marantz PM7200 Can't adjust Bias or DC Offset
Summing up how that problem was resolved (thank you to all who contributed!!):
I replaced fusible resistor 3315 that had gone very high.
And lowered 3301 (and 3302) to 220R to bring DC back within adjustable range (7267 and 7268 having drifted?)
Now will be replacing lots of electrolytics, all other fusibles, and putting back 7289 that i blew up (remember: discharge those Caps!), to reenable Protection. Looking for that 2SA970 and other through hole legged critters i discovered...
mossieurclo
New Member
Last Activity: 11-12-2020, 02:27 PM
Joined: 09-30-2020
Location: Petite Nation Valley, Montpellier, QC
-
Re: Marantz PM7200 Can't adjust Bias or DC Offset
I got the meter and solder pump today.
I calibrated the meter, rigged pins and alligators to extend the ZIF socket, tested a few cans in my NOS and 7267 of the Marantz that i had taken out (it's good :-().
That puny meter looks useful.
For Google customers searching, a pretty good manual (not supplied with the lower priced item from Amazon.ca) for "LCR-T4 Mega328 Component Tester" is here:
[url]https://kookye.com/download/manual/mega328_transistor_tester_user_guide-[/url]......Leave a comment:
-
Re: Marantz PM7200 Can't adjust Bias or DC Offset
igottheshieldsoff igottheshieldsoff igottheshieldsoff igottheshieldsoff
! ;0 GOT THE ;O SHIELDS ;D OFF ;"!!!!!!!
Leave a comment:
-
Re: Marantz PM7200 Can't adjust Bias or DC Offset
I ordered a mega328 esr meter, and a solder sucker. 1 week?
I tested a lot of a lot of diodes and fusible resistors, those i thought could be tested in circuit. All tested ok.
A lot more tests to do, especially after i remove the copper shields. I at least succeeded in tinning the old butane irons (ECG J-500 and big tipped Portasol T1), those could help.
So i plan to annotate a .pdf with my readings and post it, hoping someone more experienced than i will be there to read it and advise....Leave a comment:
-
Re: Marantz PM7200 Can't adjust Bias or DC Offset
Yeah, i read about the light bulb safety device. I did not expect to go look for incandescent bulbs again ...
And there are no FETs around. I kind of scrutinized that schematic trying to figure things out, i would have noticed
Ordered an ESR/component tester today, and a solder sucker to replace the shopvac
Next steps are: finish removing that damn copper shield, testing the fusibles, and probing that first stage.
thank you...Leave a comment:
-
Re: Marantz PM7200 Can't adjust Bias or DC Offset
Ah, well... i am really looking for that bugger.
Would you have an idea of the more likely guilty party??
I did spot 2 slightly bulging caps, but on the right side! (yes they will get replaced), but the described trouble is on the left.
Will be probe happy for a few days......Leave a comment:
-
Re: Marantz PM7200 Can't adjust Bias or DC Offset
Yes i did adjust Bias for both Classes, before trying to adjust DC where it went crazy. And after resoldering 7265 i could not adjust either DC or Bias.
I did not go back to try and adjust Class A Bias because of fear of letting the blue smoke powering all electronics get out.
But as mentioned the 56V suplies are present as deep as i could probe.
Am now in the process of removing the copper shield (i'm just about ready to try with a torch) over the first stages to probe...Leave a comment:
-
Marantz PM7200 Can't adjust Bias or DC Offset
Thanks for reading me:
After i repaired the speaker protection board of that amplifier, all was ok.
So I then proceeded to adjust iddle current, got it, then DC offset. Oh, bboy.
At that stage, on the left channel, after first seeing normal readings while moving the trimpot to get to the correct setting, suddenly readings were all over the place and did not respond to my turning the trimpot.
I played music to earphones, to find that there was no sound on left channel. Only distorted crackles on peaks.
I took out the board... -
Re: New Members - please post your introductions here
Ah? is this how i introduce myself???
So, then: retired longhaul truck driver. Fingerstyle guitar player. Amiga user. Linux user. Learner of too many interesting things. Good cook i'm told....
And repairer of my stuff, by necessity and curiosity.
Here seems a nice place ;-)
HereLeave a comment:
No activity results to display
Leave a comment: