dead sx 880

[john stumpf]

well my 880 that i had lent to a friend died after two years. i recapped it and did the solder job on that ultra hot transistor with a homemade extra heat sink 3 yrs ago . got it back today and found the following,i checked dc it is bouncy and unstable but well within parameters idle current steady and was off very little but adjusted fine. set is NOT in protection. with head phones on can hear FAINT music in right channel only and the volume pot does vary it. its about the same volume you would expect on a crystal radio.deoxit all the switches with no result, i didnt really expect much as he said it was playing fine and just went silent. any ideas on where to start?

 

[john stumpf]

i found it!!!!! r433 was open and r432 was out of tolerance and changed r119 and 120 for good measure. is there a list of replacement semiconductors that should be changed for reliability?

 

[dlucy]

If you were to list the transistors from the service manual here, you might get more or quicker answers.

 

[dlucy]

is there a list of replacement semiconductors that should be changed for reliability?

There is a thread with the base recap BOM here http://www.audiokarma.org/forums/in...l-need-some-advice.370783/page-4#post-5909763

But it didn't seem to list but one particular transistor.

 

[john stumpf]

i can do that, but i was hoping that maybe someone had concocted a list of failure prone parts as it seems to be a common set. ive got it apart and am busily checking for distressed and out of spec resistors and have found three that were way out. that, and a regrease after a thorough cleaning was the plan. ive got a lot of spare stuff and its not doing any good in the box hence the question. i did notice a a726 transistor on the tuner board and was wondering if it is ok to change it to a 992 with out screwing the tuner up.by the way that r433 and r432 really run hot. ive no way to measure them but its a bit toasty to me they are mounted off the board anybody know? after an hour theres a slight discoloration in the center of both of them

 

[dlucy]

i did notice a a726 transistor on the tuner board and was wondering if it is ok to change it to a 992 with out screwing the tuner up.

Sorry, I don't know enough to give you a definitive answer on that one. I've read many threads where people change out the electrolytics and the tantalums, but nothing else since they "don't want to have to realign the tuner". I would guess that a change of the operating curve of a transistor (replacing one known-noisy 2SA726 with a modern, much-better 992) would be a big change in that tuner circuit.

However, if you're already pulling everything out to test the components one-by-one, there is no harm, in my humble opinion, in temporarily swapping in a 992 for a 726, testing to see if you've disturbed the performance of that section of the tuner, then deciding to leave it in or revert to the 726 based on that result.