Capacitor suggestions for 1982 tape deck

[Sam08861]

PCB 2 - (correction from above... 23 caps... Mic Amp, PB Line Amp, Level Display and 1 cap for headphone amp)



Didn't see any polarity/silkscreen discrepancies on this board. The 100uf were only available in 50v, hopefully there's enough room for them, or they may have to be replaced.

 

[Sam08861]

Last one is PCB 1 and it has 91 caps, so breaking this down into ~10 smaller sections by function. I'll try to do 1 or 2 sections a day. The 2 items I didn't find on the schematic are labeled unk. (C233/C234 - red squares)

C117/118/119/120 for the PB amp, all had one leg that was corroded to the point of being loose. Hoping this (or the ill measuring 220uf/6.3 on the PB amp) is my playback issue as I didn't test yet after addressing that one.

Since HK didn't lablel the pcb with functions, this marked up layout may be helpful to others:

 

[Sam08861]

PB amp section... I found a couple of corroded traces, so extended some cap legs to make the connections or the reverse side, so some are tilted.

No polarity/value discrepancies here.

 

[Sam08861]

Power supply area - Wanted to get the glue out as I saw a number of furry green legs in that area so documented and pulled the caps in that area. I used 70% iso so it could dwell a bit and seemed to soften it up pretty good.



Holy corrosion! Seemed to be mostly around the area of a diode's leg. Assuming this got hot and wicked/heated the glue and corroded. Will have to check the continuity of the traces on back.



So much nasty!



Cleaned up, but maybe a few screwdriver scrapes. Worth the tradeoff and I'll be a bit more careful on the next area.



Of note is that the caps in the pbamp area that had corroded traces were also areas where there's glue.

 

[Sam08861]

Power Supply area done:

1 schematic vs. actual discrepancy:

C751, which is correct in the service manual parts list, but listed at 4.7uf on the schematic and, physically on the board,was 2.2uf, matching the SM​

Of note here is that for all of the items that had glue/corrosion, I had to clean the pads 3 times with 91% alcohol and a tootbrush to get the solder to stick to them. (2200uf and 1000uf caps) Noticed this in the pb amp area also for the corroded legs, but they only needed 1x cleaning.

The resistor with green legs next to the large 2200uf tested 756ohms and specced for 840, so left it alone for now. Not exactly sure how to test the diode that had the lovely green stuff, so leaving that alone for now. I'll have to check continuity before moving onto the next section.

 

[Sam08861]

Music Sense section - no discrepancies found here



C953 is over by the PB board and not next to IC951 like the rest.

 

[Sam08861]

Getting those leaky blue caps out of there is 100% right to the folks who mentioned that!

A couple more corroded areas spotted:

These are under a light blue capacitor with corroded legs.



As are these, and looks like I may have to bridge a couple of traces. Hopefully these are the only ones and I'll have to see if it's easier from above.



Feeling that that once I address these and the remaining leaky caps, it will put me in a much better position to troubleshoot in earnest. Fingers crossed!

Going to have to give both sides of all pcbs a thorough scrub before putting back together, with all the flux and spittle balls from the times I reset the vaacum on the desoldering iron or brushed the tip on the brass wool.

 

[Sam08861]

One of the pb amp caps where the pad was completely corroded and I couldn't get the solder to stick. Extended the cap leg to the next component.

Verified no contact with the solder below with a multimeter. For my own piece of mind, I might have to come back and cover that with some non-conductive liquid tape I have around here somewhere.

 

[Sam08861]

No discrepancies with dolby NR leds, remaining logic power caps and the unknown function items.

Logic power caps in corner of board


Dolby NR LED caps


Unknown function (c233/4)


A good place to stop for the evening, have a cokcktail and think about how I'll deal with that corrosion. I'll do a quick test again tomorrow before resuming.

Remaining items are Rec Amp and Rec Line Amp/MPX and the Dolby NR pb and rec sections. I'll try to one section a day and get it done.

 

[dankik]

I might have to come back and cover that with some non-conductive liquid tape I have around here somewhere.

You can use RTV to insulate the board jumper.

 

[Sam08861]

Thanks dankik! I happen to have a couple of tubes!

 

[Sam08861]

PCB 1 continued --- The Record Amp/Record Line Amp/MPX sections.

No silkscreen/schematic discrepancies here.


A bit crowded in th rec amp due to available voltages in a couple of places.


Dolby Record and Playback sections remain and have a number of the leak/corrosion prone light blue caps

I'll have to see how the caps relate to the corroded traces on the back to see if any might facilitate a bypass of the affected areas in these remaining areas.

 

[Sam08861]

You can use RTV to insulate the board jumper.

View attachment 3209401

Would you also recommend using this under the caps that had glue to replace that? Or is it better to use some other type of non flexible adhesive? (or leave it alone?)

 

[dankik]

Typically, I do not glue down the new capacitors - just solder them. But, at work if we needed to stake down a component to prevent vibration from shearing it off we would use a dab of RTV. Even with shipboard electronic equipment subject to shock & vibration of pounding seas and engine vibration we would not stake components down unless we needed to seal it against salt and moisture from getting in through the leads on non-MIL parts. If you still want to do it, just put a very small dollop in one area where the component meets the PCB.

 

[Sam08861]

Gotcha. That makes sense.

Thanks again

 

[Sam08861]

For the corrosion in post 47, picture 2, making slow progress.

On the neighboring trace with the spotting, I was able to scrape away the oxidation and use some solder to re-inforce. The mask over it flaked away easily as the corrosion was under it, helping the process a bit.

The other trace from the corroded leg won't seem to accept solder, but I'm going to continue to work on it to see if I can get it clean. Have the back up plan wire already installed, but I'm going to try some 1000 grit glued to an eraser in lieu of a fiberglass pen to see if it will clean enough.

It may be too far gone, but I'll give it 15 minutes. Looks like I'll need to remove and reflow the solder from the pin below it as it looks very dull, and maybe oxidized on the outer layer.

I've marked the other area that needs attention in the lower left with an arrow, so I don't miss it later.

 

[dankik]

I clean the pad/lead with 97% isopropyl alcohol, then use a flux pen to coat the pad and lead, then apply solder. Sometimes solder does not "stick" because of oxidation on the pad or lead.

Are you sure that the jumpers are soldered to the right places? Something doesn't look right.
From the photo, I can't tell what components and pins you are jumpering.
Does your SM show the board traces on a board layout diagram, the one I have doesn't.

 

[Sam08861]

I clean the pad/lead with 97% isopropyl alcohol, then use a flux pen to coat the pad and lead, then apply solder. Sometimes solder does not "stick" because of oxidation on the pad or lead.
View attachment 3211286
Are you sure that the jumpers are soldered to the right places? Something doesn't look right.
From the photo, I can't tell what components and pins you are jumpering.
Does your SM show the board traces on a board layout diagram, the one I have doesn't.

Thanks Dankik. I've got a syringe type flux applicator and did use that, but ordering a flux pen and a fiberglass pencil as I too think the trace can be repaired.

The picture is probably confusing due to perspective and some 'aerial cap legs'

I put solder on the trace just above your red line on the left for the repair of one side. Where the solder is, is where the corroded trace was.

The lead with the x on it is just a flying lead for a test fit and isn't soldered to anything. The yellow area is OK.

The black wire is the same as your green marking, but the at the top, the cap leg is sticking out and bend over to the left a bit so I could take a better picture and see what was going on.

Where your ? with the circle is, is where the solder that wouldn't stick to the trace globbed onto, lol. It's actually a cap leg that needs to be soldered, but got soldered unintentially prematurely, lol.''

 

[Sam08861]

This might be easier to visualize and thanks by the way for double checking things. I truly appreciate it.

The black wire is wrapped around the leg that's coming from the corroded hole. Hopefully that won't be the final solution and I can get the trace repaired.

 

[Sam08861]

1/2 of the record dolby nr area.

The circled cap in the left rear is the one where the corrosion is and I'll need to come back to it to either fix the trace or deal with the loose lead through the hole.

A bit tight fit due to the 220uf and 470uf caps unavailable in 16V. (they are 35v and 25v, respectively)

These two caps were glued down and and the glue spread into several components where it's quite crowded, so a bit slow going here due to the clean up, in addition to dealing with the corrosion on the back side. A portion of the glue had reached the corroded cap on the left and all the way to the transistor on the right. There's still a bit of glue on one of the legs you can see.