Phill's 2252

[goldswimmerb]

So I said I would make a thread for this, just getting around to look at it. Never seen one with quite this issue, amp board looks like it got very very toasty.

There's melted plastic on the top above the amp board:


And the plastic caps on both main filters are rounded from heat, and there's several shrunk casings on the amp board.



What I've noticed is that protection kicks in if the volume is turned up above 1/4 without any load. There's no DC measured on the input from the Preamp and the DC on the output before the relay closes is negligible. Going to see what the bias is at given the heat issues. Betting on bad MV-13 diodes but at this point who knows.

He did take great shape of this unit though, frontplate is pretty much perfect.



Once I track down the issue this one will be getting a full rebuild.

 

[Philbin]

You know how when you get hit by a car, and the first question your mother asks the doctor is, "Did he have on clean underwear?" That's how the inside of my amp makes me feel - definitely needed a cleaning.

Do you think the overheating could have anything to do with stacking components, i.e.- not enough air flow through the unit? Seems very localized though, and my CD player's right rear foot is toasted, the residue of which you can see in photo #1.

Thanks again, goldswimmerb, for taking this on.

 

[JJCalvillo]

Not an expert, but I doubt stacking is what caused the problem, unless whatever was on top had zero space and cut off ventilation. Keep in mind there are side vents on the 52 as well. Seems much more likely something internal is overheating. Goldswimmerb would know better though.

 

[goldswimmerb]

Not an expert, but I doubt stacking is what caused the problem, unless whatever was on top had zero space and cut off ventilation. Keep in mind there are side vents on the 52 as well. Seems much more likely something internal is overheating. Goldswimmerb would know better though.

So now testing the pre-out/main in it would seem that its definitely a main amp issue. going to be digging deeper...

 

[goldswimmerb]

You know how when you get hit by a car, and the first question your mother asks the doctor is, "Did he have on clean underwear?" That's how the inside of my amp makes me feel - definitely needed a cleaning.

Do you think the overheating could have anything to do with stacking components, i.e.- not enough air flow through the unit? Seems very localized though, and my CD player's right rear foot is toasted, the residue of which you can see in photo #1.

Thanks again, goldswimmerb, for taking this on.

Still not certain as to the overheating, however I do have it working normally now, it appears some really bad capacitors in the relay Circuit we're keeping it from staying closed, not 100% certain why it was opening with a normal signal but the failed cap may have caused it to detect a smaller amount of DC as the cutoff. Now onto the important work the rebuild

This was supposed to be 47uf for example.

 

[goldswimmerb]

Just as I thought everything was going nicely the unit decided to fight back, had got new bulbs in (the fuse for the lamp Circuit was toast) rebuilt the PSU, and rebuilt the amp board, with a new pre driver (given a KSC2690) and matched KSA992S as differential pair. I also replaced the MV-13 diodes with 2x1N4148s.


Tested on DBT fine, then decided to crank it off the DBT when, at high volume, R758 burned up and Q724 popped. Not sure what caused it, but maybe maladjusted bias? I need catrafter or someone else with more expertise to weigh in on if that makes sense. I replaced Q723 and Q724 with BD140/BD139 as I had them on hand and they seemed to be listed somewhere as a working replacement in lieu of KSA1220/KSC2690 devices.

Unit is back up and running though not sure why the driver transitor blew, it may also have just been leaky to start with and finally gave out.

 

[catrafter]

Here is what I posted as a response to the PM you sent.
'I wonder if you had incorrect bias.
I also wonder about Q734 and Q004.
If a driver fails, (Q724) I always replace it complement (Q723) as well.
Ditto for outputs, if Q004 fails Q002 gets changed too.
This is 'best practice' in complementary amp repair, the stress of one transistor in a pair failing can damage the other, sometimes (secondary failure? SOA violation?).

Max power is dissipated in the amp when the amp is run into a dummy load such that about 2/3 Vpp is across the load. Vpp is the sum of the positive rail and the negative rail voltages without regard to polarity. In a 2252 (-40, +40) = 80V times about .6= 48Vpp, about 17VRMS( sine wave), or about 36 watts into an eight ohm dummy load.'

Tom

 

[Philbin]

I'm looking through my fingers in horror.

No, that's not what it sounds like. It's more like watching how the sausage is made. Not knowing anything about electronics makes it worse, of course. I'm kind of on pins and needles.

But I trust goldswimmerb's skills and those of you who have taken an interest in this project. My heartfelt thanks to you all.

 

[JJCalvillo]

I'm looking through my fingers in horror.

Not to worry. Better this stuff happens on the test bench, where he can fix it.

 

[Philbin]

Yeah, I think I'm going to stop following this blow-by-blow for a few days. You guys just talk amongst yourselves.

 

[goldswimmerb]

Yeah, I think I'm going to stop following this blow-by-blow for a few days. You guys just talk amongst yourselves.

If it makes you feel better, the two boards I've done are below.

Amp board:


Gave it a new power relay as a preventative measure, has new driver transistors in the right channel since one decided to spontaneously explode (don't worry, better it happens here than on you). All Electrolytic Capacitors replaced with quality modern equivalents. Small value (6.8uf and below) swapped to film, new matched differential pair Transistors which have been heatshrinked and thermally bonded, new predriver transistors, and I gave the outputs new thermal paste since the original paste was completely gone. I also swapped one of the relay drivers over to KSC2383 as one of the tranistors there tends to be troublesome. Pretty much anything that could be done, was done to the amp board.

You just get to see and hear of any Carnage on the bench here as it helps to have more eyes on a single problem.

Also, below is the power supply:

Upgraded a few of the filtering Capacitors in capacitance based on knowledge of what said caps do and based on improvements seen in other units. Most caps were left the same size as original. I did use 105C rated parts since this board always tends to run hot.

Some guys disagree with the increase but I've always found it to make a positive difference as the original Capacitors were generally limited by physical size.

The main power tranistor was replaced with an MJE15032 which has significantly better power Handling than the original underrated part used. Also swapped the garbage dual diodes over to MUR1620 devices.

Up next will be the preamp. Then I'll get the tuner knocked out, the FM section of the tuner seems to tune just fine but doesn't always like to play audio, not sure if we have a dying cap or tranistor or if it's just dirty.

 

[Philbin]

Yes, this info does make me feel better. I appreciate being kept in the loop. Please don't think I'm looking over your shoulder in any way. Just had a momentary lapse of reason. You're the expert on its guts. I just get to listen to the fruits of your labor.

I guess a lot has gone wrong since 1977, but it feels like a resurrection-in-progress. I thank you for your dedication to this. All of you.

 

[goldswimmerb]

Yes, this info does make me feel better. I appreciate being kept in the loop. Please don't think I'm looking over your shoulder in any way. Just had a momentary lapse of reason. You're the expert on its guts. I just get to listen to the fruits of your labor.

I guess a lot has gone wrong since 1977, but it feels like a resurrection-in-progress. I thank you for your dedication to this. All of you.

Time takes it's toll on all of us, human and electronic

 

[goldswimmerb]

Yes, this info does make me feel better. I appreciate being kept in the loop. Please don't think I'm looking over your shoulder in any way. Just had a momentary lapse of reason. You're the expert on its guts. I just get to listen to the fruits of your labor.

I guess a lot has gone wrong since 1977, but it feels like a resurrection-in-progress. I thank you for your dedication to this. All of you.

All that's left now is the tuner, got the preamp/tone board and phono board done. I used Nichicon UES and UPW for the electrolytic caps on this board due to lead diameter.

Tone board:

Upgraded the input films to WIMA, the local DC filter cap was upgraded to 470uf if I recall (it's been a few days). The 10UF caps were upgraded to Nichicon UES as I ran out of 10uf UFG Capacitors. All small value Capacitors were upgraded to WIMA films, and I replaced the Transistors here with matched KSC1845/KSA992s, which while not necessary should offer some improvement given the lower noise of the modern parts.

Phono preamp:

Here I upped the local DC filter Capacitor to 220uf. Small value lytic caps were replaced with WIMA films.

 

[goldswimmerb]

Got the tuner board done as well, FM issues seem to have been a Bad HA1137. I also reflowed the solder for the HA1196 as a precaution. Hope it's not sacrilege to use a pioneer chip...

Lots of small value caps here, went with a whole lot of WIMA films, Overkill but reliable and guaranteed to last.


Lastly, some post restoration glory shots:


These things are beasts too, seem to be able to get about 75 watts before clipping, dont have a distortion analyzer to see the THD at that output level though.

 

[rBuckner]

Ain't it a purty thing? I love the looks of this series. Nice work and no, it's not sacrilege to use a Pioneer stamped IC! There's about a 99% plus likelihood it was made by the same manufacturer. Hitachi I think.

 

[Philbin]

Many thanks to goldswimmerb and all of you for your shepherding of this rebirth. What a great community this is!.

Cheers,

Phil

 

[JJCalvillo]

Nice work. I've been digging up different pieces and turning them. Never thought my 2203B would be leaving, but I got an offer I couldn't refuse for a 2252. Recapped it and will NEVER let it go. Plenty of muscle and great looks.

Oh yeah, it's featured in Vol. 100 of Tone Audio this month, in the Old School column.

 

[Philbin]

Thought you all might like to see the fruits of goldswimmerb's work. The 2252 is alive again, thanks to him. It sounds just as sweet as I remember. If anyone needs any rescue refurb of vintage gear in the Southeast (or anywhere else for that matter) I recommend him highly.

And thanks to this great community for helping with this restoration. I really appreciate it.

 

[Philbin]

Sad news.

This is Phil, whose Marantz 2252 you restored over the winter. It died a couple of days ago, with a short fizzing and flicker and then blackness. There is a slight "electrical" smell coming from the back right corner area, which, if you remember, experienced a great deal of heat prior to the unit being refurbished.

I've been putting a lot of uninterrupted hours on the unit lately.

I hope you find this of interest, as it has distressed me very much to have the unit back and then lose it again.

Phil