On to the next SS chassis rebuild

[Rep]

Ok, the next chassis I want to repair is blowing the F1 fuse about 2 seconds after it's turned on. I read thru some old posts that suggested either T1 being bad or bad power diodes on the heat sink. Any other suggestions as to other causes? I believe we have spares of both so it shouldn't be a problem, I was just curious if there could be some other causes. Thanks in advance. 3 chassis down 3 more to fix [img]/content/btubb/images/%%GRAEMLIN_URL%%/smile.gif[/img]

[Mark Anderson]

Re: On to the next SS chassis rebuild

[Rep]

Re: On to the next SS chassis rebuild

Okay, the diodes will be done first then [img]/content/btubb/images/%%GRAEMLIN_URL%%/smile.gif[/img] The fuses I checked out and replaced the f1 fuse holder with a circuit breaker to save some fuses until I get this fixed, but there was a 3 amp in the holder blown from before. Hopefully this weekend I'll have time to start on this chassis if not sooner. As for that other chassis man do I feel dumb lol That thing sat back out of service for over 6 years (it was sitting on the floor with a note when I started there) and to think all that time it was just a bad relay and a backwards card Makes it worse that I didn't catch that sooner. Oh well all is well now [img]/content/btubb/images/%%GRAEMLIN_URL%%/laugh.gif[/img] Thanks again for the help guys [img]/content/btubb/images/%%GRAEMLIN_URL%%/laugh.gif[/img]

[Dutch]

Re: On to the next SS chassis rebuild

Rep,

Did you get a copy of my "chassis problems & cures" that Felix posted a link to about a month or so ago? It mostly talks about the old 5 boards but with a little common sense it can be applied to MK-70's. There's also a section that is about the other chassis components. Chassis Problems & Cures

[TheGMan143]

Re: On to the next SS chassis rebuild

Wasn't there something about the T1 transformer mounting sagging, or the diode sink getting bent & causing F1 blowouts? I never had anything like that happen, so I'm a bit unclear on the details.

[TheLegend]

Re: On to the next SS chassis rebuild

Something like that was said.

I added to it the possibliity of a loose nut or screw grounding out either one. Which is what I ran into more than once.

[Rep]

Re: On to the next SS chassis rebuild

Yes Dutch, that will come in VERY handy especially at the other house I work in from time to time as he still runs the 5 boards over there. I checked the heat sink, nothing loose or grounding there. The bracket for T1 is fine, not grounding on the heat sink. Unless there's some other causes I'm guessing it's gotta be either the power diodes or T1 itself as those seem the most common causes. Thanks again for the replies, and thanks for your sheets Dutch [img]/content/btubb/images/%%GRAEMLIN_URL%%/smile.gif[/img]

[toon30s]

Re: On to the next SS chassis rebuild

Very informative Dutch!!! Does anyone have anything similar for the 82-30s?

[Rep]

Re: On to the next SS chassis rebuild

Welp, I started it today (didn't have the time I hoped to have) Replaced quite a few burned C1 pins and tried to fire it up to see what happened. Everything came on, I heard a buzzing noise, masking unit lights were DIM and after maybe 5 secs or so poof, popped the breaker for F1. The dim masking unit lights make me think heat sink, probably the diodes. Hopefully tommorrow I can change them out. Any tips to make it nice and easy (never changed em before). Hopefully tomorrow I'll have another working spare chassis [img]/content/btubb/images/%%GRAEMLIN_URL%%/smile.gif[/img]

[Rep]

Re: On to the next SS chassis rebuild

One more thing. Can you guys suggest a good tester for checking chassis stuff? We have an ancient multimeter, it works but I wanna get a GOOD tester for myself and keep it with my tools. Any suggestions for me? Just need something that would be good for 70's Any suggestions are welcome. Thanks again guys [img]/content/btubb/images/%%GRAEMLIN_URL%%/smile.gif[/img]

[TheGMan143]

Re: On to the next SS chassis rebuild

I've used a BK PRECISION "Test Bench" DMM for years... has the usual functions (voltage, resistance, diode test, etc...), but will also test capacitors and transistors. Not as useful as it used to be with the 5-boards, but still works good.

I keep a decent analog multimeter around, too. One thing a DMM absolutely CANNOT do is accurately check switches. The sampling rate is too low to catch noise...it will only show basic continuity... but an analog meter needle will dip or wiggle if a switch is noisy, and will stay dead-on still if the switch makes good contact. "Noisy" switches on the S- or T- cams will cause all kinds of havoc.

[Rep]

Re: On to the next SS chassis rebuild

Thanks for the info there "G" [img]/content/btubb/images/%%GRAEMLIN_URL%%/smile.gif[/img] I'm booming right along with my project. Changed the power diodes in the one chassis, good as new, not blowing F1 at all now. The other chassis just needed new sweep contacts installed, runs great! 5 down one more to go! [img]/content/btubb/images/%%GRAEMLIN_URL%%/laugh.gif[/img]

[Rep]

Re: On to the next SS chassis rebuild

Well, my little project is finally done. Another nice easy one, new sweep and table contacts. Now we have 3 good spares on each side of the house. Thanks again for the help guys [img]/content/btubb/images/%%GRAEMLIN_URL%%/laugh.gif[/img]

[TheGMan143]

Re: On to the next SS chassis rebuild

I'll pass on another 'tip' for checking switch or contactor contacts... instead of looking for a little wiggle of a meter needle, there's a way you can very easily HEAR a noisy switch.

Radio Shack sells a little battery-powered amplifier... about $13.00 in the store. It's part# 277-1008. It uses a 1/8" mono headphone plug as an input. If you attach a set of good alligator clips or hook-clips to a 1/8" connector and wire, you can use it to "hear" a noisy contact:

Connect the clips to the switch, making sure that the connection points are clean and secure. Turn on the amplifier, and depress the switch slowly. A clean, solid contact will register as a 'click' or 'pop', followed by silence in the speaker. A noisy/dirty contact will 'click', and the make a scratchy, static-y sound while it is held in.

That amp can also serve another function... I have to locate the part number and manufacturer, but there is an electronic version of the original "mechanic's stethoscope" (another VERY useful tool for gearbox, motor, & bearing work) out there... it uses a transducer that can plug into the amp to "hear" the internal sounds of a piece of mechanical equipment.

[Rep]

Re: On to the next SS chassis rebuild

Had a chassis go on me tonight, thought I'd throw it out to you guys. I finally finished the last bit of rebuilding on one of the old ones, replaced the elco block and about 2 pins on the chassis side. All is well and dandy right? WRONG! Now the chassis burns up something on the MK-70 (bottom left part of the board, dunno if it's a diode or what, it's right under the big black block, there's 2 of them there, redish/maroon color) It's the bottom one that burns. I checked where I soldered the new elco pins in to see if maybe I accidentally crossed something on the motherboard, didn't see anything and I checked it with a multimeter, no reads of anything crossed? Any ideas for me? If I can find a pic of an MK-70 I'll show ya exactly what keeps burning up on me.