SAE 2400L Repair

[hamrules]

Got the jacks today, there in. So I’m going to hook it up to the tuner and let it play for a few hours and see what we get. Also got the 2200 finished up, the offset is right around 9mv both sides. The current is at 1.16vdc both sides and I set the bias at 10mv. Also need to hook up to the tuner for a few hours. Then check them out and re-adjust.

 

[hamrules]

I still have to get some double sided foam tape off the front. I’m wondering if heating it up is the best way.

 

[llwhtt]

Your quiescent current is 1.16VDC across the 68 Ohm resistors? That's higher than what I've been getting on the two boards I've done. Notice how low that is compared to the 2400 even though it's the same circuit. I thinking SAE adjusted a few resistor values to make that stage run cooler as those TO-202/220 transistors run pretty warm with no heatsink attached. I ended up putting some Aavid 577202B00000G heatsinks on them.

Craig

 

[hamrules]

Your quiescent current is 1.16VDC across the 68 Ohm resistors? That's higher than what I've been getting on the two boards I've done. Notice how low that is compared to the 2400 even though it's the same circuit. I thinking SAE adjusted a few resistor values to make that stage run cooler as those TO-202/220 transistors run pretty warm with no heatsink attached. I ended up putting some Aavid 577202B00000G heatsinks on them.

Craig

Oooopppppssss, I checked the wrong resistors. I will check the correct ones later tonight or tomorrow and post.

 

[hamrules]

Have you ever replaced a fan in a 2400? I have a new one from another project but the airflow is opposite and with the housing pieces around it I don’t see how I’d get it wired up.

 

[llwhtt]

Never had to order a new one, all my fan problems, noise, was from the top cover. Pretty quiet without the cover installed.

 

[hamrules]

I still have to get some double sided foam tape off the front. I’m wondering if heating it up is the best way.

Put 90% alcohol on it and got the foam part off, messy but off.
Heated up the glue part with a heat gun and scrapped it off with a plastic scrapper so it wouldn’t scratch.
Soaked the residual remains with 90% alcohol and rubbed it good.
All nice and clean now.

 

[hamrules]

Oooopppppssss, I checked the wrong resistors. I will check the correct ones later tonight or tomorrow and post.

It’s not totally warmed up yet but it’s at about .69mv and .59mv, is that an issue that they aren’t the same?

 

[hamrules]

The 2400 was up for an hour and a half and I re-adjusted. Offset 3mv equal to or less. QC is at 1.596vdc both sides (I stopped fiddling with it). Set bias at 9.1mv across both resistors. I was shooting temps and man those amp boards and components run hot on both sides of the molex connector. The components there are from 140 to 175 F. Then everything is more normal in the 90ish to 110’s.

 

[llwhtt]

That's normal for the big resistors on the drive boards, were the circuit boards darkened from the heat? I use Vishay PR0x resistors in those locations with pieces of Teflon tubing for lead spacers.

Craig

 

[hamrules]

2400L & 2200 back together --> Done.

 

[hamrules]

That's normal for the big resistors on the drive boards, were the circuit boards darkened from the heat? I use Vishay PR0x resistors in those locations with pieces of Teflon tubing for lead spacers.

Craig

Same ones I use. I just kept them off of the board but not so fancy. Where’d you get Teflon tubing so small?

 

[llwhtt]

I have 1000 ft spools of 20ga and 18ga, but 22ga and maybe 24ga are the most popular but I only have a few feet of both. I'm going have take the plunge and buy some from Mouser, TFT20022 is the part # @ $80 for 100'. If you want some 20 or 18 I can send you some if you want, 20 might work OK for standing resistors on. Let me know. Raising resistors off the board without any support on the leads can pop the trace off the back of the board if the resistor gets bumped.

Craig

 

[hamrules]

Never even thought of that about the traces. I’m going to have to look at this Teflon stuff and see. I have a bin of pieces of that old stuff that is some kind of woven material, white in color from parts I have de-soldered.

 

[hamrules]

I see there is all different sizes if that stuff. If you used a boat load of it a 1000’ reel is way less.

 

[llwhtt]

I got both of my spools for about $20 each at a local surplus junk store. Unfortunately I don't have the need for those sizes very often but couldn't pass up the deal.

Craig