• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Philips 7871 issues

noprayer

noprayer

Super Member
Well, i hooked it up (my new 7871) :sigh: last night after checking the dc offset and noticed that the volume in the left channel is a little louder than the right and that with the volume turned all the way down i still have sound coming from the left channel. I would like to figure out what is causing this. The dc offset in the left channel was pretty high but not dangerously so, 54mv or so. Could this be the cause of still having sound come through with the volume turned all the way down? It does this no matter what i have the cd player hooked up to, meaning the tape inputs or the aux input. The right channel was around 34mv and i can hear a faint signal coming through but the left is loud enough to cause some concern. Any help would be greatly appreciated!
 
Last edited:
Register to hide this ad
Aaarrgghh!

O.K. after a wicked good cleaning (F%$&!n radio shack 10 bucks for about 8 drops of de-oxit!) i still have the same problem. The left channel has sound with the volume turned all the way down. I also noticed a slight his in the right tweeter if you put your ear next to it. Is there anything i can do? Also, do any of you Philips owners here know if there is a service manual available? I did a quick check on the internet but couldnt find one.
 
Also, do any of you Philips owners here know if there is a service manual available? I did a quick check on the internet but couldnt find one.
Click to expand...

check with brian , i know he has a few but i dont know if he has the 787.good luck with your troubleshooting.
chris
 
I must temper my earlier post with fact that even though this is happening it still sounds great to me. I'm more concerned that this issue may in some way cause damage to this receiver. I'm not even completely sure sometimes that the left channel is louder. It almost seems like it may be louder only with some frequencies and not others. Particularly in the high end. I dont know if this makes any sense to anyone (i might just be a wack job) but that is how it sounds. I think. Once again, thanks for any and all help.
 
I'm not even completely sure sometimes that the left channel is louder. It almost seems like it may be louder only with some frequencies and not others. Particularly in the high end. I dont know if this makes any sense to anyone (i might just be a wack job) but that is how it sounds. I think.
Click to expand...

this sounds like a tracking problem with the voume control .alot of times volume controls dont start tracking right until after the 9'oclock positon or higher.if the sound evens out after those positons or higher i wouldnt worry .as for the frequency losses.id recommend what e/w suggested and clean the pots not just on the volume control but all of them.
chris
 
I did clean everything while i had it open and gave them the recomended treatment with special attention to the volume. I called my electronics guru friend and he suggested i bring it over so he can teach me how to use an oscilloscope. I still would like some suggestions on where to look though. I like going over there with a good start on tracking down a problem. He thinks it is either a physical problem with the volume control or something in the pre-amp section. I'm actually glad now that this is happening because i have always wanted to know how a Silly-Scope (as he calls it) works.
 
Well, another bit o sadness to report. The power switch no longer works and it is stuck on. I turned it on this morning and it would not shut off. I found out that this unit spent a few years as a music on hold system many years ago so it spent all of that time turned on and tuned to a local radio station. But it did spend this time in a climate controlled room in the basement that is extremely clean. Could being turned on for 3 years have anything to do with the power switch failure? Has anyone ever brought a bad power switch back to life?
 
If I remember when I opened mine, the switch is nothing more than a slide switch and open to the environment. First try a series of healthy hits of contact cleaner with no lubricant. Also between the hits use a really good blast of canned air.
 
Cool. Good advice. It appears that it should come out easy enough. I just need to desolder a bunch of tabs holding the front metal plate on. I'll start tomorrow night and see what i can do while the manual makes its way here.
 
7871 Update

Seems as though i have turned this weekend into a "clean my gear" weekend. The 7871 had been shelved for some time as i have been up to my ears in other projects. I pulled it out today and gave her an extra super good cleaning and i pulled the power switch and bathed it in Deoxit. Well, it worked! The power switch is alive and functioning again and the volume issue seems to have been corrected also. The volume is even in both channels again. I still have a rather high dc offset (about 50mv in the left and 43mv in the right) but with no dc offset adjustment that i can find it will just have to stay that way. So i think i am going to put this one back in the rotation and set it up in place of my SX-850 tonight. Thanks all for the advice even though it took me awhile heed it!!
 
Congrats on getting it going. These are well laid out and should be easy to work on. Only issue mine has is that after leaving it for a time on station, there is slippage of the dial string when I turn it in either direction. Then I will turn it in the opposite and it works. Rather odd. Need to find some dial string dressing; years ago make by GC. Really like the turns per inch for tuning. A tad slow but really helps in fine tuning.

The 787/7871 is IMHO the best deal out there today on that certain site. The series is just not noticed thank goodness.
 
I might be on to something

I happened to touch the capacitor pointed out below while the meter was hooked up checking dc offset and when i touched the cap the dc offset went mental! So i checked it again and if i wiggle that cap it makes the offset jump up to about 80mv and then down to about 15mv. I think i am going to rat shack tomorrow to see if i can get some replacement caps for it. The solder joints seem solid enough so i am thinking that the cap itself is the culprit.
 

Attachments

  • Philips-cap.jpg
    Philips-cap.jpg
    126.2 KB · Views: 31
You must log in or register to reply here.
Back
Top Bottom