Help needed on testing a Rotel RX-400
- Thread starter woostersoz
- Start date
R624 seems to be OK
Still not real comfortable with only the one output blowing. Also, why did Q610 fail. Gotta look further.
Q608 and Q606 should be checked, not possible for incircuit test, however first test the bias trimmer VR602
woostersoz
Member
The bias trimmer is just variable resistor. Measure ohms using multimeter. However ALWAYS power off/unplug the unit
else sparks may fly followed by a length trip to the bathroom to clean up the mess. Testing VR602 to confirm it has not
failed OPEN or SHORT. Maybe VR602 has failed causing the bias transistor to go into overload and push the driver/output
transistors too hard???
woostersoz
Member
woostersoz
Member
Hmm.. Q606 seems to check out OK. But Q608 shows the same reading between B&E, B&C regardless of whether the +ve terminal is on B or the -ve one. It doesn't show an OL unlike what it does for Q606 - does that mean Q608 is bust?
Bias transistor Q608 NPN should read 650mV with red probe on base
and OL with black probe on base. If you are doing the measurement
in circuit then it's not valid as there is an alternate path from
base to
- collector via VR602,R614
- emitter via VR602, R616
Your tests confirms there is no short in Q608 which is the main point.
If you removed then tested Q608 then results indicate suspect faulty
Q606,8, VR602 appear ok, maybe you just got lucky with Q610. Replace failed
transistors and power up with DBT
and OL with black probe on base. If you are doing the measurement
in circuit then it's not valid as there is an alternate path from
base to
- collector via VR602,R614
- emitter via VR602, R616
Your tests confirms there is no short in Q608 which is the main point.
If you removed then tested Q608 then results indicate suspect faulty
Q606,8, VR602 appear ok, maybe you just got lucky with Q610. Replace failed
transistors and power up with DBT
woostersoz
Member
Sorry - to clarify, I removed both Q606 and 608 before testing them.
Given the results I got from 606, should I replace it?
Thanks
Given the results I got from 606, should I replace it?
Thanks
Yes Q608 should be replaced. Q608 is the bias transistor, its failure could mean one half of the amp being driven harder that the other so an output/driver
could fail. SM has Q608 as 2SD571(ecb), 2SC4793(bce) looks like a fair match apart from the reverse pinout. Hopefuly someone will chime in with a
better match.
woostersoz
Member
petehall347
the brandy coffee man
2SC4793 is maybe hard to find .
Oldsansui441
Super Member
A KSD1616A or a KSC2690A would work well as a replacement. Did you replace all driver transistors when you replaced Q610? Also it would be best to match whatever you do in the faulty channel in the other channel also.
Oldsansui441
Super Member
In regards to Q606, if you only get a reading in two postitions of your six way diode test referring to mbz's diagram, then it will be ok.
Apologies for the advice on 2SC4793, was working off my own inventory, got a handful left. Noted Mouse has a back order for 300 odd, due early Dec.
Might grab a few more.
Recommendations for Oldsansui441 appear on the money, re:subs and no need to replace Q606 if it tests OK
Might grab a few more.
Recommendations for Oldsansui441 appear on the money, re:subs and no need to replace Q606 if it tests OK
woostersoz
Member
Thanks.. if this channel works correctly after all the replacements, I will go ahead and make similar replacements on the other. To summarize what I am planning to do with the faulty channel - can you pls provide your thoughts?
1. Q614 (Original 2SC1826) - replace with 2SC1826 that I got off the auction site
2. Q610 (Original 2SC1384) - replace with NTE 293.
3. Q608 (Original 2SD571) - confusingly, the interweb points to NTE 293 as the replacement for this too? Should I instead replace with KSD1616A or a KSC2690A as noted above?
4. For good measure, in case Q606 (or others of type 2SC1318) fails - replace with NTE 289A.
1. Q614 (Original 2SC1826) - replace with 2SC1826 that I got off the auction site
2. Q610 (Original 2SC1384) - replace with NTE 293.
3. Q608 (Original 2SD571) - confusingly, the interweb points to NTE 293 as the replacement for this too? Should I instead replace with KSD1616A or a KSC2690A as noted above?
4. For good measure, in case Q606 (or others of type 2SC1318) fails - replace with NTE 289A.
Fairly busy/only a few minutes here and there.
Apologies, don't like your plan.
Rule 1, don't buy semiconductors from that auction site (fakes)
Rule 2, Don't use NTE (Cr@p)
I'm sure the learned AK members can come up with some better subs,
A good suggestion already made is replace Q608 (2SD571, ecb) with KSC2690A
Q610 2SC1384(ecb) ???
Q614 2SC1826 ???
Apologies, don't like your plan.
Rule 1, don't buy semiconductors from that auction site (fakes)
Rule 2, Don't use NTE (Cr@p)
I'm sure the learned AK members can come up with some better subs,
A good suggestion already made is replace Q608 (2SD571, ecb) with KSC2690A
Q610 2SC1384(ecb) ???
Q614 2SC1826 ???
Oldsansui441
Super Member
Hi, l wouldn't trust parts off the auction site. Do yourself a favour and order known genuine parts through one of the larger retailers like Mouser, Digikey, Newark etc. Also NTE parts don't have a great reputation around here either.
2SC1826 can be replaced with KSD526Y. You will need to replace all four though. https://au.mouser.com/ProductDetail...GAEpiMZZMshyDBzk1/Wi4G1GLBZKHK1aaGJ%2bHYgaG4=
2SC1384(r or s) can be replaced with KSD1616A (y or g) or KSC2690A (y) also.
2SC1318 (r or s)can be replaced with KSC2383 (y).
Hope this helps.
2SC1826 can be replaced with KSD526Y. You will need to replace all four though. https://au.mouser.com/ProductDetail...GAEpiMZZMshyDBzk1/Wi4G1GLBZKHK1aaGJ%2bHYgaG4=
2SC1384(r or s) can be replaced with KSD1616A (y or g) or KSC2690A (y) also.
2SC1318 (r or s)can be replaced with KSC2383 (y).
Hope this helps.
Oldsansui441
Super Member
Sorry my reply was an in progress and l didn't see mbz's reponse first, as he said buy genuine parts and you will have no problems 
.
.woostersoz
Member
Thanks. I have placed the order at Mouser. Will update here once I have replaced the components. Btw, built myself a DBT last week so hopefully won’t fry more parts
