2245 Bias Transistor.

[quaddriver]

A note on hfe matching and disparities - pick a machine to do it, and stay with that machine. we dont know how it is measured internally to the machine and what parts are used and in the way, so consider hfe as a relative measurement, not an absolute.

I note that if I use my dmm and measure up a few feet of ammo tape one day, if I come back 6 months later and do it again, the numbers tend to be lower because my batteries are weaker, or its warmer, colder etc. on they day you do a matching exercise, the temp is the same, the battery condition is the same, the snowfall is the same etc. when I come back later and try again and the numbers are lower, say a hfe of 400 one day and 390 the next, I also find that the hfe395 trans are now 385 - so the drop (or gain) is consistent.

if I have 1845s at 400, I will consider 399-401 the same so I measure up 2ft of ammo tape, write down the hfes on the tape and when I come in later, I can quickly get 4 of a similar hfe at a glance. (and Im down to 70 with my order still backordered)

 

[Steven Tate]

Looks great! Nice job.

 

[Dearslayer]

Thanks guys. I was worried because at first as I had the leads on the J post recommended as per the SM and was not getting a reading at all. A little search here on the forum revealed that I was on the wrong locations for this particular unit with the higher serial number. Onward through the fog to the next board.

GT.

A note on hfe matching and disparities - pick a machine to do it, and stay with that machine. we dont know how it is measured internally to the machine and what parts are used and in the way, so consider hfe as a relative measurement, not an absolute.

I note that if I use my dmm and measure up a few feet of ammo tape one day, if I come back 6 months later and do it again, the numbers tend to be lower because my batteries are weaker, or its warmer, colder etc. on they day you do a matching exercise, the temp is the same, the battery condition is the same, the snowfall is the same etc. when I come back later and try again and the numbers are lower, say a hfe of 400 one day and 390 the next, I also find that the hfe395 trans are now 385 - so the drop (or gain) is consistent.

if I have 1845s at 400, I will consider 399-401 the same so I measure up 2ft of ammo tape, write down the hfes on the tape and when I come in later, I can quickly get 4 of a similar hfe at a glance. (and Im down to 70 with my order still backordered)

Good point to note Quadriver. Think I'll do that with the ones I have left. Your right in saying the drop or gain was relatively consistent. I did notice that, regardless of the device used to measure.

GT.

 

[Dearslayer]

Finished the 150/300 boards and decided to change the bulbs to LED’s and velum behind the meters before moving onto the 400 board only to discover that there is no vellum on this unit behind the meters. Looks like there never was. No remnants of old paper to be seen. Is it common for the 2245 to not have vellum at this location and should I put some there anyway? Hmmm ...don’t recall any of the other Marantz units I restored not having it there.

 

[Steven Tate]

Don’t know if it was left out from factory very often, but I would put new velum behind them if you are going LED. They are a little more of a hot spot than incandescents.

 

[Rasputin47]

That is correct, Marantz did not put velum behind the meters on earlier production units.
That seems to have been a running change though, and AFAIK, they did put velum behind the meters on those models later on.

I had a 2245 from 72, and have a 2245 and a 2270 from '73 and none of them and velum behind the meters, which I added during the rebuilds.

I'm curious, what is the build date on your 2245?

 

[Dearslayer]

Well I was pretty tired last night after work but I knew it would bug me if I didn't install the vellum so I went ahead and did it before calling it a night. This unit is from '73 according to the date stamp on the front of the unit.

 

[Dearslayer]

Ugh! So I change out the function lights with the new 8v LED’s as well as the Stereo lights. Everything worked before with the old bulbs. Put it back together and the stereo light works but the function lights don’t. Checked that I had all wires soldered and nothing noticeable out of place but still no go. So I pull the bulb tray out and jumper it temporarily and the lights all work but as soon as I screw the tray back in the housing and solder up the connections the function lights don’t work again but the stereo light does. Note: the resistor in the photo gets really hot when it’s all put in place and soldered up but it doesn’t get hot when the tray is out and it’s all jumpered and the lights work. Is there a grounding issue.Any ideas??

 

[petehall347]

looks like something is shorting

 

[Steven Tate]

I had a similar problem once and it turned out to be a wire on the meter end of the board where power goes from the board into the meter housing that was shorted to chassis. Probably unlikely, but it pretty much has to be a short, and the fact it works when out kind of rules out solder bridges or something like that. A lot of wires move around when you pull that board back. Check them all and check around the meter housing if you don't find it elsewhere.

 

[Dearslayer]

It’s weird because everything looks to be ok but I also know that it could be something really simple and stupid that I’ve overlooked. Lord knows it wouldn’t be my first time. I’ll check again tonight after work.

 

[Dearslayer]

Came home from work tonight thinking I'd find out one way or another where the short might be. I've poked/ prodded / and manipulated with a wooden stick every wire visible while it was still on the DBT with no luck,and as soon as I pull the tray out of the the housing all function lights work just fine. Very fustrating. Where do I go from here?

 

[Dearslayer]

Just an update with regards to the grounding issue… don’t know what the problem really was, but I probed all wires and connections multiple times and it made no difference whatsoever or so it seemed and finally I was about to give up on it and I installed the light tray back into the housing and all worked just fine. I’m glad it works but it bothers me that I don’t know what the issue was to begin with fearing that the issue could possibly return at any time. Oh well I guess I will have to deal with it at that point and time… Now onto the next question I have. I’m replacing the power switch ( the lights flicker when powered on until it stabilizes ) and the one contact on the switch is much worse than the other I guess from arcing. I have the snubber cap I had ordered from Dojo but it doesn’t have the inline resistor that I have read about. I’m gonna wire it the same as the old switch but would like confirmation that I’m doing the resistor correctly as in the crude drawing below. Sorry my artistic skills are somewhat to be desired.

G.T.

 

[petehall347]

some light reading for you here .
https://www.allaboutcircuits.com/technical-articles/safety-capacitor-class-x-and-class-y-capacitors/

 

[Dearslayer]

Thanks so much petehall347. Very interesting read but as a laymen in the true sense and at the risk of sounding completely stupid, it may take me some time before I can truly understand what it all means. Hopefully I learn a little as I go every time I attemp something I haven't done before thanks to the wisdom of the fine folks here that so willingly offer up some expert advise.

GT.

 

[petehall347]

i am far from an expert . i just look at where the current might flow and cause things to burn up . then check everything .

 

[Dearslayer]

Well I went ahead and installed the new switch with cap and inline 120ohm resistor. Fired it up and DBT was fine. So far it seems to be working ok. No bulbs flickering. Photo of new switch and also the old one. Check out the burnt and degraded contact on the old switch.