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Marantz 4230 right power amp board is missing H705 (2SC1318Q)

vferdman

vferdman

Active Member
I am currently working on a new project. A 4230 with right channel not working. I opened it up and saw the power amp board partially taken apart and clear signs of attempts to repair. The efforts were abandoned and left in a state of disarray. The rest of the receiver looks untouched and original. Left channel sounds weak. Probably needs a recap and some TLC. Looking at the right side amp board I see H705 missing from the board. From the service manual I can see it's supposed to be a 2SC1318Q or R. I already ordered a kit to recap (and then some semiconductors). But while I wait I would love to populate that empty transistor spot and see what happens.

This brings me to the question at hand. What is a good substitution for this transistor in this circuit? I am attaching a schematic of the amp board.

Marantz 4230 Power Amp Schematic.png
 
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dankik said:
If you check the AK transistor substitution guide here:
https://audiokarma.org/forums/index.php?threads/marantz-transistor-diode-trimmer-sub-guide.926805/
It suggests to use a KSC2383YTA.

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Thank you very much for that link and the chart! I tried KSC2690 (sub 2) because I happen to have a few of those on hand. No joy, but 40W bulb stayed dim on the DLT. I ordered a kit to recap and replace select semiconductors. The left channel that does produce sound produces it horribly. I at least want to get the power supply refurbished before I troubleshoot the right channel. I just thought that by some luck I may be able to get he right channel up and running with replacing the missing transistor. No luck on that, but I am neither surprised nor discouraged. Will update the thread on my progress and I am sure ask questions as I go along. This is my first 4230. I do have a few 2270 and 2230 done as well as two Pioneer 1010 and some Onkyo and others. Still learning the vintage hifi ways, but I am an old electronics guy, so not totally ignorant. Very glad for this resource here. You guys are awesome!
 
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Update.

I have refurbished the power supply and the left channel power amp. It now sounds very good (on the left side, right side is dead). It sounded tinny and weak. I now tested it into a dummy 8 ohm load with 1kHz tone to 38 watts before clipping. The sound is very nice and strong to my ears.

The right power amp has two shorted outputs and the other two are not measuring very good values, but not dead short as the others. So I am in need of four replacements for 2SC789 transistors. What are some good replacements for this application?

Thanks in advance.
 
Update.

Just ordered some TIP31BG transistors from Mouser. Hope those will work. From what I read it seems like they are a good replacement for 2SC789. Please comment if you have experience, knowledge or suggestions.
 
The AK transistor substitution guide has TIP41C as a sub for 2SC789, in stock at Mouser and Digikey. I have personally not use this.

1709440726846.png
 
dankik said:
The AK transistor substitution guide has TIP41C as a sub for 2SC789, in stock at Mouser and Digikey. I have personally not use this.

View attachment 3136541
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Thank you for that chart! I ordered some TIP31 from Mouser. I think that one is also appropriate. If it doesn't work I'll try TIP41. They are not very expensive, which is great.

I am still not sure what went wrong with the right channel and whether refurbishing it with new caps and transistors will address the problem. If anyone has any insights into the power amp of this model, I would be very happy to hear them. I understand that this amp can be powered up without the output transistors connected and checked for bias and other voltages. Is this correct?

So far the channel that does work sounds really good in a true Marantz way. So I am hopeful to get this unit restored and playing.

Thank you again for the great resource!
 
Update.

I replaced the outputs on the right side of the 4230 with TIP31. Still no sound on that channel. Measuring voltage between J711 and J717 I get crazy 10V (yes, volts! not millivolts). When I turn off the power the voltage stays on those pins for a very long time, like several minutes. DLT Bulb is dim and left channel is working properly. I will now start measuring voltages going back into the circuit and see where I get sane measurements. I have replaced all the electrolytic caps and most transistors. Will also make double and triple sure everything is in correctly. Though all the new transistors are in the package with the same ECB orientation, I believe.
 
vferdman said:
Measuring voltage between J711 and J717 I get crazy 10V
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Any why are you measuring the voltages between these two points? If anything, you should measure the voltages from J721, J719, J717, J711, J709, J707 to ground. (But you need to be careful because when you go from 4 channel to 2 channel modes, the main amps do not use a ground reference.
1709997612588.png
 
dankik said:
Any why are you measuring the voltages between these two points? If anything, you should measure the voltages from J721, J719, J717, J711, J709, J707 to ground. (But you need to be careful because when you go from 4 channel to 2 channel modes, the main amps do not use a ground reference.
View attachment 3142267
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I am following the service manual for setting the idle current. That is where the manual says to measure and adjust the idle. J717-J711 and J718-J712. I do have the unit in 2 channel mode. My scope has the ground floated, but I am not using the scope yet. I am just using my multimeter.
 
dankik said:
Yes, I see. Maybe this thread will provide some answers?
https://audiokarma.org/forums/index.php?threads/4230-quadradial-help.917985/page-2
Also, this:
https://www.olegvintageaudio.com/2023/03/marantz-4230-receiver-restoration.html
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Thank you. I will take a look.

Update.

As of this moment I found big emitter resistors (0.5 ohm 3W) to be bad. To be precise, 3 out of 4 are open, one is ok. One of the bad ones crumbled in my hands as I removed it. Something must have fried it. I ordered some replacements and we shall see how it goes.
 
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vferdman said:
Thank you. I will take a look.

Update.

As of this moment I found big emitter resistors (0.5 ohm 3W) to be bad. To be precise, 3 out of 4 are open, one is ok. One of the bad ones crumbled in my hands as I removed it. Something must have fried it. I ordered some replacements and we shall see how it goes.
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Shorted outputs can do that before the fuse pops. To be safe, check the value on the fuse if it didn't blow! I've seen up to 20A ones stuck in units!!
 
rBuckner said:
Shorted outputs can do that before the fuse pops. To be safe, check the value on the fuse if it didn't blow! I've seen up to 20A ones stuck in units!!
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Very good idea to check the fuse! I will definitely do that. There was evidence of very ignorant attempt at repairing this thing. All kinds of incompetent soldering and such. Thank god, it was limited to that amp board. The rest of the receiver is untouched. I will definitely look at the value of the fuse, though. I am using a dim bulb setup, of course with a 40W bulb in it. But that is a good call to check the fuse value.
 
beaubiffle said:
I bought the amp board kit from ebay and did my right board on my 4230. Worked great. It had all the caps and all the transistors.
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I did the same, but my kit did not come with output transistors and it didn't come with emitter resistors as both of those items do not usually go as part of normal use. The kits sold on ebay are normally to refurbish, not repair amp damage. I bought some output transistors from Mouser, but discovered the resistors to be open, so ordered some of those and waiting for them to arrive now.
 
Update.

I have replaced the emitter resistors (0.5 ohm 3 Watt) and now am getting a bright bulb. If I disconnect two outputs (out of four) that handle the negative side of the signal (H002 and H004), bulb goes normal and I can listen to the good (left) channel just fine as before. I found two bad diodes, the ones near the pots. Replaced them, no joy. Found what appear to be bad PNP A684 transistors. They test open all directions. I am not sure what I can replace those with. They are 1A collector current transistors. Not sure what an adequate replacement would be. I stuck in some smaller PNP in there (660 mA), still no go and bright bulb. I have another component somewhere that is shorted. I know it's most likely on the side of the circuit that handles the negative part of the signal. Will keep looking. If anyone knows what a good replacement for A684 PNP is, please let me know.
 
dankik said:
Look at the transistor substitution guide:
dankik said:
Look at the transistor substitution guide:
View attachment 3148847
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Thanks, I missed it. I guess it's the 2SA684 instead of A684. In any case, I don't think I have any KSA1220, hopefully they are available to buy. I still have a short to find. Also a 39 ohm resistor near that 684 looks toasty, but measures fine still. I'll have to see if I can get some of those as well.
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