LPC480 with a bum TASU

Happy Holidays everyone.

The LPC480 I'm working on would appear to have a bad TASU. The mech will do the standard scan and load the record but will not play. I have checked for the 100 VDC at the test point but I get nothing. Only once did the juke play and it was at 33 not 45 RPM. Turning the adjustment pot on the front of the TASU had no effect.

The previous owner did purchase a recapping kit and installed it but there were a few errors that I had to set right. The 1000uF cap was installed reversed and there were some changes to the original schematic included that weren't done correctly. I corrected those as well but the unit was still not working.

An examination of the other components revealed a substantial amount of orange brown waxy substance below the inductor, L751. I am concerned that the inductor is no longer viable. If that is the case, what are my options for replacement. There is no indication of the value of the inductor for me to shop out a replacement.

Up here in the Great White North, replacement units don't come along every day and if I can rebuild I'd be fine with that. While we're on the subject of the TASU, does anyone here know the values I should be seeing when checking the transformer coils to make sure they are alright as well?

Thanks,

Thom Smith

Thom, when an electrolytic cap is reverse-formed it is usually ruined and is shorted, or will soon even when properly connected.

There is a strong likelihood that it has taken components such as a tran, diodes and possibly outputs.
First, test the power tran. Remove the damaged cap and disconnect the diode bridge associated with T2101 ( http://s1192.photobucket.com/user/Rob-N ... 1.jpg.html )

Set the machine to play a 45 and look for low AC from the two red wires to chassis ground from that tran. Were it not for the evident leakage from a transformer, I'd suggest checking both the adjust pot and value of the large non-polarized cap.

Realistically, once some a-hole has tinkered and done damage, it is best to start over with another speed unit. Even if a tran shows no outward evidence of being 'cooked" it may still be damaged by burning internal paper insulation. LPC stuff is plentiful, if you are not totally set up to test all the coils or have another unit to compare readings, you are better off just salvaging a few good parts and dumping the rest. The output transistors can be used in the amp as finals.

Sorry to be the bearer of bad news.

Rob-NYC

Hi Thom,
I have rebuilt 100's of 45TSA's ( and still do so !)--never have run into a "bad choke"-- I would replace the caps, then fire it up with the "red wire" dis-connected--check for "25"AC and the "30"DC voltage at that point, should tell you if the choke, and transformer are good-
I dis-agree slightly with Rob, in that as far as I recall, the amp outputs may be used in the Autospeeds, but the Autospeed finals may NOT be used in amps-- Ron Rich

Ron, for what little it matters, I've used finals salvaged from a pink autospeed that had a really burned up tran and melted diodes.
The right hand are the speed unit transistors. They are actually slightly higher ratings than the those used in the amp. This amp came off a 16 year stint last year. the feed-throughs on the AGC board caused no control and one channel out. This was a true junkbox amp in that it was missing all finals and had only one good driver -in addition to a broken compensator switch and looking like it was thrown down some stairs....But it was $5.......and I had everything needed.
http://s1192.photobucket.com/user/Rob-N ... rt=2&o=183

Rob

Hi Rob,
Somehow one of us is backwards here--I think you are---
Amp trannies are GC 114 (or 2N457A) (309412), which are ( in my book) rated much higher, in all categories, including gain, then the GC 433's (or 2N1530) (309422), used in the Autospeeds. Ron Rich

Here are the two spec's:
http://www.datasheets360.com/part/detai ... 085778255/ -2N457A In amp.

http://www.datasheets360.com/part/detai ... 922602407/ -2N1530 A-S.

You are right that the amp transistor has the higher current rating (7A), but I discounted that at the time because it was not possible to put that amount of current through a device in that amp design.

The speed unit transistors have a slightly higher VcE of 45V. Which doesn't really matter here either.

When I look for sub's for these types of low-power and low drive amps, I just looked for VCE and case configuration.

Anyway, it woiks!

Rob

Guys,

Thanks for the replies. I will dig deeper into this with the info you have both provided.

Ron, my concern with the choke is that there is a great deal of waxy glop on the underside between it and the case. I thought that was sort of the 60's version of 'Magic Smoke' and that once it leaked out it didn't work anymore. The 'red' wire in question is the short jumper or the ones on the secondary side of T751, the ones that go to the bridge?

I have replaced the 1000uF cap and even went as far as replacing the diodes in the bridge. Should I be looking at replacing the 4uF as well? If so, I do have a 5uF on hand as long as that is acceptable. As a point of interest, the cap kit the fellow bought came with a replacement pot as well but it's a 25 ohm instead of the 4. Greater range of adjustment?

Rob, at this point with is juke it's all bad news. Not getting discouraged, though, it is the time of miracles, right?

On another note, I've started another thread about repairing a reversing relay, http://www.phonoland.com/viewtopic.php?f=3&t=7963. Please feel free to offer some advice over there as well.

Thanks in advance,

Thom Smith

Hi Thom,
It runs in my mind that I once attempted to use a 5 uf oil filled cap--did not work --can't recall exactly what it did--
as for the wax--those do have an abundance of it--and usually leak some out, without any problems, that I have ever noticed--
As far as the pot goes--it would seem 25k is a bit much--might have problems "adjusting" it ?? I use a 10 K WW.--the original was 4k., and USUALLY can be re-habbed with Deoxit-5, and a little TLC-- Ron Rich
Will look at the R relay post now--
Ron Rich

I have replaced the 1000uF cap and even went as far as replacing the diodes in the bridge. Should I be looking at replacing the 4uF as well? If so, I do have a 5uF on hand as long as that is acceptable. As a point of interest, the cap kit the fellow bought came with a replacement pot as well but it's a 25 ohm instead of the 4. Greater range of adjustment?

What is the result of powered testing?

As for the pot, a 25K will be a bit touchy in getting accurate speed. If so, you can loom (parallel) a resistor of 10-20 ohms which will bring the total resistance more within range and make adjustment easier.

...And don't get discouraged, resurrecting these old relics is always a challenge. Getting P-O'ed and having to take things apart multiple times is par for the course. It gets slightly easier with experience...but there is always some new to stink up the fun...or add to the sense of adventure

Rob

Rob,

Thanks for the words of encouragement, I figured there would be challenges just not this many all at once.

On another note, when it comes to the adjustment pot, all the schematics I look at are labeling it at 4 ohms. In the posts above we're talking about K ohms instead. The part that was included with the capping kit was a 25 ohm and the original pot had already been replaced so salvage was not an option. When I ordered a new 4uF oil filled as well as a 1000uF 35V lytic, I also ordered a 10 ohm pot. I'm hoping that it isn't a 'typo' in all the schematics I've been looking at.

I'm about to roll up my sleeves and do some measurements on the TASU as it is and then swap out parts if needed. Wish me luck.

Thom Smith

Hi Thom,
Don't understand why/how--but both Rob and I, made "typo's" there--there should not be a "K" there--the original pot was 4 ohms !
Ron Rich

Ron,

Thanks for clearing that up. So the 10 ohm I have on hand should be fine.

Thom Smith

Thom,
No problem--sorry I made that error--
If "wire wound", 10 ohm works fine--adjust after unit/motor, warms up-
Ron Rich

No problem, Ron.

Included with the cap kit were some instructions on doing some rewiring to 'correct' a design flaw when it came to grounding the pot. I'm going to go with that as a good thing. It swaps the Orange lead from T753 that originally goes to the outside of the pot and Orange/White lead from T752 that goes to the wiper and also grounds it. The explanation given is that this is a more stable ground than the original which was prone to corrosion between the frame of the TASU and the pot.

One other thing that I have noticed in my poking around is the the Red and Red/Yellow wires on the primary side of T753 seem to be labelled opposite to how they are connected in the unit. Just an observation and I'm guessing that it makes no difference to the actual operation of the unit.

Thom Smith

Hi Thom,
I am not sure why that "ground" was added--but I know it was done very late in production of the 45 TASU-2's. There seemingly is no rime nor reason for it--and I have seen it connected to either the orange, or orange/white one--whichever was connected to the outside frame of the pot (which in turn, is "crimped" to the frame of the unit) !-- As for "primary wires"--very early on in the LPC-1 run, they had a problem with the Autospeed being out of phase. This caused various 25 volt AC relays to "hang-up" at intermittent times. It may, or may not have been corrected in the schematics ? I never compared them, as you have-- Ron Rich