Marantz 2275 rebuild, saved from the dump

[rossm]

Hi Everyone !!
I have started the work of restoring my Marantz junkyard find.
As suggested I have started a new thread for this restore.
Its cleaning up fine, but we have some issues with the electronics..


First off the power relay is not clicking on, I removed the 4 pole plugs to both power amps and the relay clicked on, didn't take long to figure out the right power amp is fried. Looks like R733 R737 C716 were smoked pretty good. As I understand this part of the ckt to support the transistors of H713 and H714. Any suggestions as to what might have caused this ??

 

[Beamer302]

I just went through this a few months ago on a 2275 that looked like it had been under the ocean ! . You will have to replace the burnt parts and then check the blue transistor B537, H707& H706. I found that you should check the big white twin power resistor. it is (2) .2 ohm 5 watt resistors in one cement shell. (Mine had one of the resistors open) I replaced that part with two .2ohm 5 watt power resistors. You will have to check the Power transistors too. When they fail all this stuff gets hot and burnt like you see. Good luck. You won't need much (luck) because these amps boards are easy to work on.

 

[rBuckner]

I'd be sure to scrape/dig out all burnt pc board material while the parts are out. If need be fill in the pit with epoxy. Tom/Catrafter also adds ground pc board dust to his epoxy, just be sure to not use the burnt stuff though!

 

[rossm]

I just went through this a few months ago on a 2275 that looked like it had been under the ocean ! . You will have to replace the burnt parts and then check the blue transistor B537, H707& H706. I found that you should check the big white twin power resistor. it is (2) .2 ohm 5 watt resistors in one cement shell. (Mine had one of the resistors open) I replaced that part with two .2ohm 5 watt power resistors. You will have to check the Power transistors too. When they fail all this stuff gets hot and burnt like you see. Good luck. You won't need much (luck) because these amps boards are easy to work on.

Thanks Beamer302 good call, looks like both of the power transistors are bad. I also checked the transistors on the other power amp H002 looks fine but on H001 (pnp) I am getting 9.6M ohm between the emitter and collector. I aways though this should be open for a working transistor ?
Another good call on the R740 .2ohm 5 watt power resistors one of them was at 17K ohms, thought that was odd, so I took it out of the ckt and measured again and sure enough it was still 17K, I would have suspected open or short but 17K ? Do you recall the part number you used to replace R740 ?

Will be replacing B537(H714), H707 and H706 just because they were close to the damage,
Working on getting my list of parts together, Where did source your parts from ?

thanks for all your help

 

[Beamer302]

You need to replace the R740 power resistor block with two .2 ohm 5 watt wire wound resistors. Here is the Mouser part # 588-TUW5JR20E. Make sure when you install them to keep them up high off the board . Use the original height as a guide. Also to note that when resistors get hot they either go high in resistance or open. 17K means that resistor got hot and is on it's way to burning out (open).

 

[Beamer302]

H714 2SB537 (aka B537) replace with MJE15031G
H706 2SA733 replace with KSA992FTA
H707 2SC945 replace with KSC945
you can get these from Mouser or Digikey

 

[rossm]

H714 2SB537 (aka B537) replace with MJE15031G
H706 2SA733 replace with KSA992FTA
H707 2SC945 replace with KSC945
you can get these a from Mouser or Digikey

Hi
Mouser does not have the KSC945, but does have 512-KSC945GTA will that work ?
thanks

 

[rossm]

H714 2SB537 (aka B537) replace with MJE15031G
H706 2SA733 replace with KSA992FTA
H707 2SC945 replace with KSC945
you can get these a from Mouser or Digikey

HI
I am having a hard time finding the C716 ceramic .02 mf 50v cap at mouser, the ones they show look very different, Any help would be welcome..
thanks

 

[catrafter]

The KSC945 should be a C suffix, 512-KSC945CGBU, that way the collector will be in the center like the original.
For C716, I would pick a .02µF/50V film type with the correct lead spacing to fit the holes.

Tom

 

[rBuckner]

You could even get away with a 0.22uF I bet, which is a more standard value. Disclaimer: I did NOT look at a schematic to see what this cap does.

 

[rossm]

Thanks guys I really appreciate the help. I will order the damaged parts and also the reccomended replacements for both power amp boards, would you recommend just replacing the damaged components and trying it, or should I also replace the reccomended parts before trying it. I know the first option is more cautious but I am also worried that some of the reccomended parts could also be bad and wind up blowing the parts again.
I also ordered 2 new power transistors for the other channel, might as well have matching outputs for $10
At any rate I will have to wait until after thanksgiving before doing anything, see you then !!

 

[rossm]

Hi Again,
Well Thanksgiving is over and its time to get back on the 2175
It like Christmas with the Mouser order

I was able to get all of the toasty parts out

Here is the board with the parts removed

And now the new parts minus the H707 transistor that I need to order

Note that if you are ever replacing parts R733 and R737 there are an extra set of holes in the board, right between H706 and the proper hole for R733, I almost screwed that one up. It was nice to be able to reference my working channel to verify the proper placement. thxdave was kind enough to send me some of his extra fiber wire insulation and I was able to use it on the 2 big resistors, R740. Thanks thxdave

Some of my marginal soldering skills.
When I get the H707 installed I plan on testing the board out, if all is well I will replace the recommended parts.

 

[Beamer302]

Good job . In the picture of your soldering skills it looks like there a three pads that did not get soldered. Maybe this picture was taken before you finished soldering.

 

[rossm]

Good job . In the picture of your soldering skills it looks like there a three pads that did not get soldered. Maybe this picture was taken before you finished soldering.

Yep, hope to do that one tonight

 

[KingBubba]

To answer your earlier question, chances are very good that something else might have caused the damage and the parts you are dealing with might just be collateral damage. If you do not have a dim bulb tester, make one and use it to fire up your receiver when the work is done. Do some AK research on the DBT. There are lots of threads about making one and how to use it. Have fun.

 

[rossm]

HI all
Put the amp card back into the receiver, crossed my fingers and powered it up and it failed the DBT. I did some more poking around and looks like H709 is also bad, so its back to the parts store.
Everything in yellow has been replaced. I have checked all resistors in ckt and they look close to stated values.
I am all ears if anyone has any suggestions
thanks

 

[catrafter]

You are wise to use a dim bulb tester.
Note that the input does NOT share a ground with the output. If J710 is disconnected (or if the shield is broken), the amp output can 'latch' at one of the power supply rails.
H705 through H708 are part of the AOS circuitry. You can safely remove these until you get the amp working as long as you don't drive it hard.
H 709C should be at about +0.6VDC and H709E should be at about -0.6VDC with respect to chassis ground.

Tom

 

[rossm]

You are wise to use a dim bulb tester.
Note that the input does NOT share a ground with the output. If J710 is disconnected (or if the shield is broken), the amp output can 'latch' at one of the power supply rails.
H705 through H708 are part of the AOS circuitry. You can safely remove these until you get the amp working as long as you don't drive it hard.
H 709C should be at about +0.6VDC and H709E should be at about -0.6VDC with respect to chassis ground.

Tom

Thanks for the info Tom.
So are you saying that if the shield or ground wire on J710 is missing or broken bad things will happen to rest of the circuit ?
I should have the H709 in by next Wed.
I think that I have found part of the problem, someone had stuck a 20 Amp fuse in the unit...

 

[catrafter]

So are you saying that if the shield or ground wire on J710 is missing or broken bad things will happen to rest of the circuit ?

Yes, the shield side of the input jack must be intact and return to ground (chassis) at some point.

I think that I have found part of the problem, someone had stuck a 20 Amp fuse in the unit...

Ouch!

Tom

 

[rossm]

Yes, the shield side of the input jack must be intact and return to ground (chassis) at some point.


Ouch!

Tom

Hi Tom
Funny you should mention this, I just took a look and the ground connector is no where to be found, the input and the shield are present


The working channel does have the ground and it is screwed to the chassis

I know that I didn't remove it!! How strange

Thanks