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2230 p750 power amplifier board toasted rebuild and upgrade?

pingu_turbo

pingu_turbo

On a constant search...
Hi Guys,

I think I'm going to need some help with this one... :pity:

I must say I’m having a bit of a nightmare this afternoon with the 2230, I was using it again enjoying the sound for the last few times before the recap and the right channel all of a sudden started popping in and out and before I had a chance to turn her off, the channel died. With a little puff of smoke from the right hand side of the cabinet.

So on to the bench, covers off, right hand P750 out and I have some visibly damaged resistors and a load that don’t value properly. I checked the two output transistors H756 & 755 in situ (is this ok to do, or do I have to remove?) they have continuity across e & c but H752 I removed as I had funny values, I have nothing across e&c, dead.

The two output emitters are not spec. R775 & R774

The damage as follows:
R753 incorrect value
R756 incorrect value
R758 incorrect value
R759 incorrect value
R761 incorrect value
R766 measures ok, visible damage
R767 incorrect value
R768 measures ok, visible damage
R769 incorrect value
R771 toasted
R772 measures ok, visible damage
R778 incorrect value
R779 incorrect value

Do you have any suggestions on other components to check, do I have to remove the other transistors to test H755 & 6?

If it is as straight forward as replacing the resistors and transistor, shall I remove the left channel and check the other resistor values, and replace as necessary or do the pair uniform to one another? Obviously I want both channels the same. Or is this a perfect time to pop some good quality components in both sides?

I am an amateur when it comes to repairing amplifiers so any pointers would be gratefully received.

Please see below the P750 as it is now

Many thanks

Untitled.jpg
 
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You really should pull parts to test them accurately.

There are a couple capacitors on the board that cause havoc if they open.

I would replace every transistor on that board, every cap, every burnt resistor, emitter resistors, and test everything else including diodes.

Test the output transistors out of circuit.

Then, do the other channel.:D

Rob
 
Hi Rob,

Many thanks for the reply, that fills me with a bit more confidence. With the recap, the capacitors would be done anyway, but I wanted to make it work before attempting such a task so I know everything is functioning again before pulling it all apart.

The only thing I am concerned about now is what to replace the resistors with now. I see that in the schematics some are carbon and some are 'solid'. What kind of resistor is solid, is it the foil type? With regard to the output emitters, are these the only ones that matter to the sound, would it be best fitting a wire wound type, any particular brand?

Does it matter what the others are replaced with, I notice that metal & carbon film resistors seem to have a difference tolerance rating. Then coefficients. This is such a learning curve for a noob.... :headscrat

All I want to do, now given the opportunity, is to repair and upgrade any components I can whilst I'm in here. If I Google audio grade resistor I get bombarded with thousands of selections to make, I'm not really sure where to start. :scratch2:
 
Wonder if the coupling cap to that channel took a ****?

I wouldn't even waste my time on that BBQ'd board, there's a replacement with heatsink and opt's on ebay. Replace the coupling caps, recap the amp boards and reinstall. If you want to spend your time trying to replace all components then you calculate time vs money. You could go the long route of sourcing all the parts and come back round to the same amount, just sayin.
 
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Hi bk, frankly that would be a great idea if the seller hadn't re listed the item by mistake. :tears: I just had a message from him this evening. Also where would I find the coupling cap, is it part of this board?

So I am back to plan A, rebuilding the board. And after removing and testing I now know I need an output transistor. Is it wise to replace them in pairs? Does anyone know if there is a modern/better equivalent kicking around?
 
The coupling caps are the 2 matched smaller of the 3 Grey caps sitting left middle inside the unit. I just rebuilt a 1060 which is based off the 2230 and they were 3000uf. While your in there replace the main power cap and recap both amp boards, may as well do it now since it's apart.

Onsemi replacement outputs

http://ca.mouser.com/Search/Refine.aspx?Keyword=MJ21194G

Do all 4 if you want matching outputs, do 2 if you don't care that it's running different outputs and you plan to keep it.
 
The primary filter capacitors is C007 4700 mfd @50 volts.

The coupling capacitors are C008 and C009 which the service manual shows as 2200 mfd @ 63 volts.

You can use Nichicon KG series for all 3, pay attention to the diameter of the original capacitors and try to find new components that are the same size, so they will fit into the original clamps.
 
Ahh I see, many thanks for the info guys. I have ordered a recap kit from Robert Bowdish at I Rebuild Marantz to save me the trouble of searching for the correct value caps. With regard to the sizing of the power caps, I was going to empty out the old ones and house the new ones inside so it still looks the same under the cover. I must add Robert absolutely top chap, really helpful and replies to my emails no matter what time of day it is! Has anyone else dealt with him on here?

Anyway, has anyone got any advise on what resistors to use to replace the originals on the power amp board? I'm not sure what construction to use all carbon film or metal, or to keep the same mix as the original or even the coefficient? I'm looking at the smaller ones and also the output emitters and would I need to replace them on both boards to balance the sound?

Can someone please offer some advise?

:worried:
 
I personally wouldn't bother with stuffing the old caps with new parts, it's a lot of extra work and most people don't care if the 3 caps are new, as long as the workmanship is good.

I have been experimenting with carbon film and metal film resistors in place of carbon comp, but the jury is still out on any net improvement.
 
On the 1060 I restuffed the large cap, I had 2 3300uf coupling caps (physically smaller) and used door insulation foam to take up the gap.
 
bktheking said:
On the 1060 I restuffed the large cap, I had 2 3300uf coupling caps (physically smaller) and used door insulation foam to take up the gap.
Click to expand...

Elna LAO series 3300 uf caps are the same size as the original 3000 uf caps, then you only need to fill the gap on the 4700 uf cap
 
I have a board lying around. Are you in the states? If so I can send u the board and possibly some replacement transistors (oem) from mouser that I used to restore my 2230. What's your address.
 
That is such a generous offer, but unfortunately I am in the UK. If the offer still stands I can pay you for the board, transistors and the postage? :scratch2:

I really want to fix my beloved 2230, but I am not feeling confident about putting a repaired board back in especially when I am not really sure what I am doing. :tears:

I am doing this on a budget too so I cant afford for anything to go wrong....


Also I forgot to say thanks for the tips on the power caps and also the out put transistors.:thmbsp:
 
Baseballhack, pm sent.

petehall347 I'm not really anywhere near Worcester, I'm down in sunny Devon..... not! I have never seen weather like it just of late!

Well at the moment I am just sitting tight until the recap kit arrives from IRM. And then Ill have to sort out the blown amp board. :sigh:
 
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