More BUSH DAC10 Woes!

[DonaldStott]

Having recently restored a Bush DAC10 I felt quite confident about tackling another one when an opportunity arose - serendipity or misfortune?

That early optimism soon diminished when the chassis was removed from the case when I found: -

1. There was no frame aerial wire for the MW winding.

2. The original dual can for the smoothing and reservoir caps had been removed and a 32μF/32μF had been substituted for it at some point and just left 'floating'.

3. The bulb holder and associated wiring was in a poor state and needed replacing.

4. Some rewiring had obviously taken place but with poor quality wire, especially around the On/Off switch and Dropper.

5. Many solder joints suffered from an excess of solder and although the electrical connections tested o.k. for continuity they were indicative of poor workmanship. I won't win any prizes in the Elegant Soldering Competition but even I can do better - see below.

Notwithstanding the above, good progress has been made with Points 1-3 above and work had just started on Point 4 when I noticed that the wire from the top of the 16μF electrolytic smoothing capacitor wasn't connected anywhere under the chassis! The wire from the top of the 32μF electrolytic reservoir capacitor was, as expected, connected to one end of R16 (HT line smoothing) although this was one of the solder joints mentioned in Point 5 above: -



Now the 'Senior Moment' I am having is where should the other end of the wire from the top of the 16μF electrolytic smoothing capacitor connect to? Looking at the Circuit Diagram I would hazard a guess that it goes to the other end of R16 where a short wire connects that tag to Pin 5 of V4 - anyone??



Part of my confusion with this set is the way in which the 'Phantom' has used RED wire everywhere - maybe it was all that they had in stock?

Meantime, some more solder joints for you to peruse: -



I'll try to Post regular updates on progress.

[Keith956]

Originally Posted by DonaldStott

Now the 'Senior Moment' I am having is where should the other end of the wire from the top of the 16μF electrolytic smoothing capacitor connect to? Looking at the Circuit Diagram I would hazard a guess that it goes to the other end of R16 where a short wire connects that tag to Pin 5 of V4 - anyone??

Yes that's correct. C25 (32uF) positive connects to rectifier V5 cathode, R20 (10K) and T1. C26 (16uF) positive to the other end of R20, V4 pin 5 screen / rest of HT supply.

[David G4EBT]

Originally Posted by DonaldStott

Meantime, some more solder joints for you to peruse: -

I'll try to Post regular updates on progress.

Strewth - whoever did that soldering shouldn't be doing radio restoration work they should be doing time.

[HamishBoxer]

Think the solder was put on with a trowel!

[Techman]

Underpowered soldering iron by the looks of it.

Not unusual to see any of that sort of thing and more.

[DonaldStott]

Working my way around the various resistors I've only come across four which are measuring 20% or more over one of which is R19, the V5 surge current limiter.

This is marked and should read 150Ω but is reading 239Ω so will be replaced.

I have two options available in my supplies box but which one is more suitable - the markings are-

5W 150ΩJ

150RJ 40 OV2

[Michael.N.]

Originally Posted by Techman

Underpowered soldering iron by the looks of it.

Not unusual to see any of that sort of thing and more.

That was my first thought. Not hot enough to get the whole mass of solder to flow. It looks a little like my very first attempts to join a lead pipe to a copper pipe! (long time ago).

[ColinB]

Fairly disgusting workmanship.This set might be a candidate to strip out completely and rebuild from a clean chassis upwards?

[Silicon]

There is always a possibility that high temperature solder was used to attach/connect to the dropper resistors and someone had only a standard soldering iron.

A previous 'repairer' may have even used 'plumbers' solder.

I assume you will replace the wires on the dropper resistor with silicone insulated or other high temperature versions.

[DonaldStott]

All the wiring from the main switch to the Dropper has been replaced with silicone insulated wire from Forum member SWB 18 - thanks Phil. Also replaced the wiring connections from the Dropper to V5 (Rectifier) and to the scale lamps, the Output Transformer and the dual capacitor can. These latter connections are associated with a dual can restuffing exercise, but more on that later!

The wiring from the Frame Aerial to the Tuning Unit will also be replaced once I've rewound the MW winding - ongoing ...

In all cases the through-chassis grommets have perished and are being replaced.

Meantime, does anyone have advice on my resistor query in Post #6 above - thanks?

[Silicon]

The 250 Ohm resistor (R19) is an official modification which is mentioned on page 12 of the Bush service instruction manual.

[DonaldStott]

Originally Posted by Silicon

The 250 Ohm resistor (R19) is an official modification which is mentioned on page 12 of the Bush service instruction manual.

Thanks - hadn't noticed that in the Modifications:-



So my 239Ω R19 should be fine?

Just for the record, what does 150RJ 40 OV2 stand for?

[DonaldStott]

Originally Posted by DonaldStott

So my 239Ω R19 should be fine?

Of course it will - the actual resistor markings are 250R 20% -

[DonaldStott]

Moving on quickly from the above I've come across more evidence of work by 'The Phantom' !

It is evident that at some point the On/Off Switch-Volime Pot has been replaced as I'm assuming that the ones fitted by Bush didn't have a plastic shaft?

Connecting my DMM between the centre tag and one of the outer tags on the Volume Pot I'm measuring between 0Ω and 850kΩ as I rotate the knob! Looking at the Circuit Diagram in the Service Instructions, VR1 is shown as 500kΩ - I don't see any changes listed in the Modifications ??

[Techman]

What does it say on it? Probably a 1Meg. I shouldn't think it'll matter, it may even sound better with more bass. I've actually done the same thing myself when I've had to back in the distant past.

[Al (astral highway)]

Yep, the soldering is pretty dire. It may be that someone has bought the newer alloy of solder with no lead, which has a higher melting point than people may be used to. Also I was sold as ‘low melting point solder’ an alloy of 93% Sn, 5% Pb and 2% Ag - actually a high melting point solder!

But whatever , this is pretty award-winning for unsightly and horrendous workmanship ...I’d start again !

[Techman]

The most amusing thing about that workmanship is that although there may not have been enough heat in the soldering iron to melt the solder properly, there was certainly sufficient to melt most of the insulation on that wiring!

Using all one colour for replacement wiring is quite acceptable if you know what you're doing, although it doesn't necessarily look right or good. I've got an old radio, a Murphy I think, where someone in the past has replaced much of the original wiring with red wire, but their soldering was better and the radio works.

[DonaldStott]

Thanks for all your observations regarding the soldering - good to see so many of you giving the person the benefit of the doubt!

If anyone asks where I incurred most expense with this set the answer is easy - Desoldering Braid/Wick.

I'm also inclined to leave the On/Off Switch-Volume Control in situ, at least until such times as I can power things up!

[DonaldStott]

Making slow but steady progress with this DAC10 but didn't expect that almost every section would need replaced, rebuilt or refashioned in some way, especially the wiring!

Turning my attention to the scale lamp holder I decided against fabricating a new one from a strip of Paxolin and simply pushed a couple of grommets into place to enable me to use modern bulb holders with new 3.5V 0.15A bulbs. This avoids any possible mismatch between old and new ES threads - an area where I"ve encountered issues previously!

With the bulb holder and pointer assembly back in place it looks like this :-

.

The pre-set levers have been covered with heat shrink to ensure that there is no chance of shorting with the bulb connections - I'm fairly happy with this.

[Herald1360]

Originally Posted by DonaldStott

Just for the record, what does 150RJ 40 OV2 stand for?

150RJ is 150 ohm 5% the rest.....

Any idea of make?