Marantz 140 Power Amp – Intermittent Fluctuating Right Channel

[raidermc]

Just look at the hFE values.

 

[raidermc]

Do you have a transistor checker or a multi meter with a transistor checker built in??

 

[labatt242]

I don't have any transistor checker/multi meter. I have plans to have a good one. I will borrow that of my brother for this one.

 

[labatt242]

Did you look at the differential input pair??
Its a known issue that they will oscillate as they age out.
They are the (2) to98 transistors with the shrink tubing holding them together for proper thermo tracking.

Dear raidermc,

Is that normal that the two transistors are not tubing holding together? They are on right channel but not on the left channel. Maybe they has been overheated?

Thanks!

Guy

 

[raidermc]

They should be thermally coupled.
I have seen in the past a similar situation to yours. Maybe the last tech that serviced it forgot that last step b4 they button things up. Did you do a complete recap on the power supply board??

 

[labatt242]

They should be thermally coupled.
I have seen in the past a similar situation to yours. Maybe the last tech that serviced it forgot that last step b4 they button things up. Did you do a complete recap on the power supply board??

I didnt touch the unit since I bought it from a guy from Ebay saying it was #1.

The unit has been completely recaped with a new relay. Inside is really clean.

 

[labatt242]

I checked for cold solder and all seems fine. I will test the transistors and resistances. Quick question.... Do I need to desolder the transistors and resistances to test them? Or I can test it using multimeter directly on the board?

Thanks in advance!

Guy

 

[raidermc]

They must be removed from the pc as you will be reading a combination other components in circuit as well and it will skew your readings. .

 

[FOH Engineer]

Fascinating thread, and hope it all works out. I love my 140 and it's being driven by either my 2240 or 1030.

 

[labatt242]

Okay, I did some transistors test. Here the following :

h702 = 820, 826
h701 = 850, 899
h703 = 813, 825
h704 = 803, 801
h708 = 820, 815
h705 = 835, 845
h707 = 840, (c)0
h706 = 815, 828

I can't have read h707 Base/Collector... so I think I found the defective part.

My best bet is to change h705, h706, h707 and h708 or only the defective one?

If I am not correct, please told me

Thanks !

Guy

 

[raidermc]

I would change all 4.
I am looking at my 2275 sm as they are pretty much the same.
Those are to92s and cheap enough. Also don't forget to take care of 701 and 702. A little thermo paste on the flats and shrink tubing.

 

[labatt242]

I would change all 4.
I am looking at my 2275 sm as they are pretty much the same.
Those are to92s and cheap enough. Also don't forget to take care of 701 and 702. A little thermo paste on the flats and shrink tubing.

Alright. I will order a pack of 10 transistors for each model (KSA733CY) and (KSC945CY) to have a match I will have some spare for the other channel. I will order some heat sink tubing too from Mouser.

I will let you know the outcome.

Thanks!

Guy

 

[labatt242]

Finally, I have a local store in Montreal for the transistor. I will go with 2SA733 and 2SC945, the same parts on the manual. I saw I can use 2SC1845 to remplace the 2SC1327 instead of the NTE199. I saw too that NTE199 should be last option if no other remplacement is available.

The real question : Can I use 2SC1845 to remplace the H701 and H702 in the future?

Thanks !

Guy

 

[raidermc]

As long as the specs are close, go for it.

 

[labatt242]

I have my transistors for the h705 to h708. The only thing.... For the h701-702, the guy at the store give me the 2sc733 as remplacement of 2sc1327 (was noted NTE199 on the box as reference). Anyone have experience with this model?

Thanks!

Guy

 

[labatt242]

Dear all !

I changed the transistors h705, h706, h707 and h708. I thermaly coupled h701 and h702 as recommanded. I will test the 140 for at least 50 hours to be sure the issue is resolved. The unit is running for 5 hours and so far so good for now.

To be continued!

Guy

 

[raidermc]

Well done!!!

 

[labatt242]

Hell there !

The unit has been running fine for 2 months but this morning.... I have a constant hum/buzz from the left channel and the heatsink get hot very fast.

Is there already a post I can read?

What could be the issue?

Thank you in advance!

Guy

 

[labatt242]

Ah well, I think I resolved the issue. I compared the BIAS for Left and Right channel : left channel was 167mv and right channel was 10mv. Both channel are now 10mv. I did the DC adjustment for both channel (was -0.5v on left channel and 0.2v on right channel so was not really an issue here). Both channel are now 0v. The unit runs cooler than before. I can hear a very very little "hum" volume but I need to be about 0.5 feet on woofer hear level so I don't think it's an issue. The unit is running for about an hour and no more loud "hum" volume for now.

Hopes this post will help someone here!

Thanks!

Guy

 

[labatt242]

Hello again !

Here some followup of my Marantz 140.

Unfortunately, I still have the issue (Intermittent left channel) but I realised something : I did the BIAS adjustment 2 or 3 times since 1 month (heatsink get hot and the sound is really weird ("hum" sound make my woofer moving in and out and some "clack clack clack" sound).

I spend a lot of time of reading and I saw it's maybe the BIAS transistor H709 or/and the driver transistors H713/H714 (maybe I am wrong on that but it's what I read).

BUT!

Yesterday, I powered up my Marantz 140 and waiting for the issue. It took at least 5 hours to hear this "hum/clack" sound and I tried to freeze some transistors using a airdusting can. I tried H705, H706, H707, H708, H713, H714 no chance. I tried the H701/H702 and the "hum/clack" issue has disappear. These transistors has been replaced by NTE199. I ordered KSC1845FTA to replace again these transistor. They are shrink tubing but I realised I didn't add thermal grease between the two TO-92. I will add a piece thermal pad. Is thermal paste for heatsink/PC Parts will works?

I heard also it's maybe a diode (H721 and H720) that may be fluctuate....

I already ordered some part in case i need to replace them.

TIP29C, TIP30C for H713/H714

KSC2690AYS for H709

KSA992FTA for H703

KSC1845FTA for H701/H702

I will start with the H701/H702 and make sure they are thermaly coupled (110% sure) and shrink tubing.

I think I am in a good way.

Your thought?

Thanks !

Guy