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MARANTZ 2230 power amp. PLEASE.help.

jFF_Bulbo

jFF_Bulbo

Active Member
Hello AK'ers.

I´ve been working on a recap on my 2230. i finished the recap according the suggestions here, in AK.
main caps are new.... output transistors...... voltaje on P800 PS board are correct: 13.8v on j805 and 35.6v on j808.

P750 has new:
-electrolitic caps
part-------original-----sub
-h752-----c959-----2n3440
-h755-----c959-----2n3440
-h756-----a606-----2n5416
-h757---- bias thermistor+150R resistor------ 1N4148
-h753-----c371------ksc1845
-h754-----a562------ksa992
-h751-----c945------ksc1845
-h758&h759-----1n60----- 1n60p

also some new resitors with same value than original.

First time after recap i conected he receiver to DBT and got smoke on R771 (220R 1/2w) on both P750 power amp.
I changed h755 and R771, left chanel works fine, no resistors explodes.... DBT is ok when only this board is conected.
**************************BUT**********************************
POWER AMP RIGHT SIDE REFUSES TO BE REPAIRED.
al last 3 times h755 has been ruined and R771 still exploding....... as you can see many new parts are installed... even the 3300/63v coupling cap have been changed (twice), and the board has been recapted twice.... nothing can make r771 and h755 stop to go out of bussines. Some mj15024 output transistors has been lost on this board.
I tried to change the c762 cap (100pf) with 150 pF NP0 cap. didn't help.

IMG-20200910-001633.jpg

** front side, many new pieces**
U7MeRZN

AT THIS POINT no idea how i could fix it.

IMG-20200910-001522.jpg

**the back side**

thank you for your help.
 
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Ok, things that stand out to me:

The 2230 uses 2w emitter resistors. Not 5W.
1N60 and 1N60P are different.
The subs I have seen in the past are C371 to either KSC2383 or KSC945 and A562 to either KSA1013 or KSA733.
 
EastPoint said:
Ok, things that stand out to me:

The 2230 uses 2w emitter resistors. Not 5W.
1N60 and 1N60P are different.
The subs I have seen in the past are C371 to either KSC2383 or KSC945 and A562 to either KSA1013 or KSA733.
Click to expand...
I agree. KSC945 looks like a better sub for C371. And I’m going to change the subs for A562 on my transistor sub list. A992 was found as a recommendation in more than one thread, but KSA733 is a much better match. On both of those transistors, the subs you used had a max collector current (Ic) that was half of the original. I don’t know if that could be your problem, but its worth trying the different subs.
 
Are both boards identical regarding the components? Is bias trimmer R765 at the same value on both boards when you are switching on the unit?
 
EastPoint said:
Ok, things that stand out to me:

The 2230 uses 2w emitter resistors. Not 5W.
1N60 and 1N60P are different.
The subs I have seen in the past are C371 to either KSC2383 or KSC945 and A562 to either KSA1013 or KSA733.
Click to expand...
I agree, i also seen here the subs You say , but i also found here in AK the subs i installed are ok too. Honestly ksc1845/ksa992 are installed beacuse i have o good quantity of them.
 
sanjib said:
Are both boards identical regarding the components? Is bias trimmer R765 at the same value on both boards when you are switching on the unit?
Click to expand...

Yes. Idéntical. Both R765 are the same, 1k 1 turn trimpot. Both was set to 450 ohm before installed. This value is the same that the one in the old trimpot before it was changed
 
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catrafter said:
Do you have a good board to compare to (the other channel)?

Tom
Click to expand...
Hello, sensei Catrafter!
the other board -i guess- is fine. DBT is ok when only the "good" board is connected, and when i conectc the unit to the 120v ac outlet, it seems ok, no smoke or failure appears. So, i think this can be OK.
The next i'll do is change R768-9 (390r 1/2w). And the r771 &h755 Will ve changed... Again.
Will check 4700/80v Main cap.
If there is no energy from Main cap, the h755 trans can behave like mine, making r771 exlodes????
 
Steven Tate said:
I agree. KSC945 looks like a better sub for C371. And I’m going to change the subs for A562 on my transistor sub list. A992 was found as a recommendation in more than one thread, but KSA733 is a much better match. On both of those transistors, the subs you used had a max collector current (Ic) that was half of the original. I don’t know if that could be your problem, but its worth trying the different subs.
Click to expand...
Sensei Steven Tate, hello!
I will try changind the trans.
I can get:
2sc945 for h751 , originally 2sc945
2sc2383 for h753
2sa562 for h754.
What do You think???
 
jFF_Bulbo said:
Sensei Steven Tate, hello!
I will try changind the trans.
I can get:
2sc945 for h751 , originally 2sc945
2sc2383 for h753
2sa562 for h754.
What do You think???
Click to expand...
I think H754 was originally 2SA562. A good sub, recommended by Eastpoint above, is KSA733.
 
Steven Tate said:
I think H754 was originally 2SA562. A good sub, recommended by Eastpoint above, is KSA733.
Click to expand...
The unit had a1013 installed with c2383, For h753-4 and for the h755-6 has intalled d1138/a968 transitors (they looked horrible, if You ask me...)
I intalled c945 on h751. C2383 for h753. A562 for h754. SMOKE ON r771 with DBT....
This unit Will be hard to repair...
 
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I think your problem is not related to components rather in the trace of the board. I would take the schematic and follow all the connections on the back of the board and compare it with the good working other one.
 
You also NEED heatsinks on the 2 driver transistors 3440/5416. They're probably burning up along with an output transistor, hence the EMITTER resistor R771 smoking.
 
catrafter said:
Do you have a good board to compare to (the other channel)?

Tom
Click to expand...
Hello. This are the readings from the left board, unit plugged to 120v. Black to chasis, red to terminals.
J764---- 0v
J762----0v
J759----53.7v
J761----0.06v
J760----54v
J758----54.2v
J756----71.5v
J757----54v
J755----71.5v
J753----71.5v
I can't ser the bias. No matter how i adjust r765, i always have 20mv un j757-j759. From a short time after adjust r765, bias esa 8.4mv, then ir claro m quickly until 20mv.....
R760 don't ajuste DC , ALWAYS READS 54.2v between chasis and J758......
Maybe with two 1n4148 un series i could set the bias.... or Even intalling the old thermisto +resistor..... But DC OFFSET???
 
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