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 Post subject: Very low output voltage on Heathkit IP-27
PostPosted: Aug Tue 13, 2019 4:06 pm 
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Hi,

I've changed all the capacitors on the my Heathkit IP-27 LV power supply and also checked the pots and they are perfectly fine. After that I followed the calibration procedure as per the manual. But one issue I faced is that the max voltage for all the voltage selections are 5V lower and for the last two selections are 8V lesser. I checked all the resistors on the selectors and they seemed to be fine. I checked the film capacitors and they are good too.

Apart from the lack of getting max voltage when the fine knob is fully clockwise the power supply works fine with proper voltage regulation. Has anyone faced such an issue?

Thanks in advance.

Link to the schematic of the Heathkit IP-27 LV power supply:

https://www.nostalgickitscentral.com/heath/schematics/heathkit_schema_ip27.pdf

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Last edited by Vintage Collector on Aug Wed 14, 2019 10:56 pm, edited 3 times in total.

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 Post subject: Re: Max Output voltage for all voltages less on Heathkit IP-
PostPosted: Aug Tue 13, 2019 4:20 pm 
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Maybe recheck that the new capacitors are good? I suspect poor filtering, causing insufficient supply voltage.

Does the output stop increasing in spite of turning the adjustment, or is the end of range too low? It could be an error in the voltage reference.


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 Post subject: Re: Max Output voltage for all voltages less on Heathkit IP-
PostPosted: Aug Tue 13, 2019 8:27 pm 
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Manual is here
http://www.rsp-italy.it/Electronics/Kit ... supply.pdf


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 Post subject: Re: Max Output voltage for all voltages less on Heathkit IP-
PostPosted: Aug Tue 13, 2019 8:50 pm 
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The reference voltage adjusts to 50v with no issues?


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 Post subject: Re: Max Output voltage for all voltages less on Heathkit IP-
PostPosted: Aug Tue 13, 2019 10:57 pm 
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If you connect another voltmeter of reasonable accuracy across the output, what do you see? If the supply makes rated output on an external meter but the internal one is five volts off, that’s one problem. If the supply cannot make rated output on any meter, that’s another matter. Also, do the semiconductors look original? In the timeframe this was made, Heathkit transisors had 417- part number prefixes, zener diodes had 56- prefixes and silicon diode rectifiers had 57- prefixes. If sekiconductors have been replaced with generic substitues the unit may no longer function correctly.

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 Post subject: Re: Max Output voltage for all voltages less on Heathkit IP-
PostPosted: Aug Wed 14, 2019 6:14 am 
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I'd check all the transistors with an ohm meter. I encountered a shorted emitter-collector on one of the large transistors on mine. There's another ARF thread on the IP-27 and alternate replacement transistors are mentioned.


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 Post subject: Re: Max Output voltage for all voltages less on Heathkit IP-
PostPosted: Aug Wed 14, 2019 8:35 am 
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Location: Powell River BC Canada
I have an IP-27.

Your voltage at the output terminals must be tested with load resistors,
and in conjunction with the current range, and settings.

To get output, you need current. Back off the current, the supply goes into
a constant current mode, and the voltage is controlled by the load.


Also make sure the cutout relay contacts are clean.

The IP-27 is primitive, in that it uses a variable tapped secondary
as main voltage control, and regulates at the various steps.

You cannot ramp up the voltage from zero to 50.

Read page 36 of the manual.

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 Post subject: Re: Max Output voltage for all voltages less on Heathkit IP-
PostPosted: Aug Wed 14, 2019 6:46 pm 
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Hello everyone,

So, after going through all the feedback from you guys I have come up with some results. Also I've update the link to the schematics in the original post.

As you can see there is a table in the link for the schematics that shows the voltage outputs at points E1,E2 & E3. First I'll post my output voltages at fine voltage adjustment pot at maximum clockwise portion. The voltage readings were taken with a good multimeter.

.5 - 5V = 3.36V
5 - 10V = 5.53V
10 - 15V = 8.28V
15 - 20V = 11.08V
20 - 25V = 13.8V
25 - 30V = 16.55V
30 - 35V = 19.35V
35 - 40V = 22.0V
40 - 45V = 24.9V
45 - 50V = 27.7V

These are the voltages I get with fine voltage knob at maximum position for each voltage selection.

Next here are the readings I'm getting for E1, E2 & E3. Each of these voltages are with the fine voltage knob at maximum counter clockwise position for each voltage range selection. Input power supply= 110.4VAC

E1 (AC voltage):
9.6 VAC
14.3
18.9
23.5
28.5
32.5
37.1
41.4
46.7
50.7

E2 (DC voltage):
12.56 VDC
18.98
25.4
31.8
38.7
44.2
50.6
56.5
63.7
69.2

E3 (DC voltage):
0 (even when I tried the knob fully counter clockwise it was still 0V)
1.84 VDC
4.18
6.59
8.91
11.26
13.68
16.03
18.44
20.8

Now I'm currently gong through the manual section for troubleshooting which talks about what to look for when the output voltage is "No output" or "Low output voltage"

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 Post subject: Re: Max Output voltage for all voltages less on Heathkit IP-
PostPosted: Aug Wed 14, 2019 7:07 pm 
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As I mentioned earlier, check for 50v at the reference supply. If voltage not there, it is easy enough to trace that one out.


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 Post subject: Re: Max Output voltage for all voltages less on Heathkit IP-
PostPosted: Aug Wed 14, 2019 8:12 pm 
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Scott wrote:
As I mentioned earlier, check for 50v at the reference supply. If voltage not there, it is easy enough to trace that one out.


Hello Scott,

Is the measurement for the reference voltage taken across R13 15 ohm at points A & B? Because I'm getting 30.2VDC at that point.

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 Post subject: Re: Max Output voltage for all voltages less on Heathkit IP-
PostPosted: Aug Wed 14, 2019 8:36 pm 
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Vintage Collector wrote:
Scott wrote:
As I mentioned earlier, check for 50v at the reference supply. If voltage not there, it is easy enough to trace that one out.


Hello Scott,

Is the measurement for the reference voltage taken across R13 15 ohm at points A & B? Because I'm getting 30.2VDC at that point.

No. Check out the numbers in the ovals. Those are voltages taken with respect to the negative output terminal. The voltage on the right hand side of R14 (voltage calibrate) needs to be 50v. The E3 voltages will not be correct if it is not 50v, and your E3 looks wrong. If you don't have the 50v, work your way back in the reference voltage section until the voltages become correct - that is, match the numbers in the oval.

Also, double check the polarity of the capacitors you put in.


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 Post subject: Re: Max Output voltage for all voltages less on Heathkit IP-
PostPosted: Aug Wed 14, 2019 8:48 pm 
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Measurement of the DC voltages inside power supplies like this one is devilishly confusing.
You must use the main "minus" (-) output terminal of the power supply as the "0V" reference point for measuring the voltages labeled on the schematic.
And you must follow the Heathkit manual in order to put the controls and switches into the required positions while doing these measurements.

Important items:
The reference voltage section starts out with a separate winding on the power transformer and goes through 3 filter capacitors, 3 series resistors (one of these is adjustable), and 3 zener diodes on the way to the output voltage control. That's rather more complicated than it needs to be, but evidently it's what the original design engineer wanted. It is probably a bit more stable because the voltage is gradually regulated down to a lower value by each of the 3 zener diodes.

You should be measuring DC voltages that are close to what's indicated on the schematic. The voltages in this section are positive in regards to ground, except for one specific point (I'll get to that later).

Positive terminal of C1: approximately 210V. It is OK if this is 15V higher or lower than 210. The voltage isn't regulated at this point.
Junction of R1, R2, and Z1: This should measure close to 105V. +/- 5V is OK.
Positive terminal of C2. This should measure very close to 65V.

Now here's where it gets more complicated:
There is a specified "zener current" which is adjustable via variable resistor R3. It must be adjusted to the value given in the Heathkit manual. When this zener current is correct, the voltage across R9 (and C6) will be close to 5.7V. Note that the value labeled on the schematic is negative with respect to the (-) output terminal. That is correct.

Check the polarity of C6 very carefully. The positive terminal of C6 is connected to ground (the - output terminal of the power supply). It would be very easy to put this capacitor in backwards.

After confirming that C6 is correctly wired (positive end of C6 to (-) output terminal of power supply), then if you still cannot get 5.7V across R9, I recommend carefully checking the out-of-circuit resistance value of all resistors in the reference supply section. These are R1, R2, R9, and R13.

Evidently there is a switch that permits displaying "zener current" on the power supply's built-in meter. But this requires both R9 (200 ohms) and R13 (15 ohms) to be accurate in their resistance.

My suspicion rests on the possibility that C6 is miswired with the wrong polarity.

-EB


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 Post subject: Re: Max Output voltage for all voltages less on Heathkit IP-
PostPosted: Aug Wed 14, 2019 8:52 pm 
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Scott wrote:
No. Check out the numbers in the ovals. Those are voltages taken with respect to the negative output terminal. The voltage on the right hand side of R14 (voltage calibrate) needs to be 50v. The E3 voltages will not be correct if it is not 50v, and your E3 looks wrong. If you don't have the 50v, work your way back in the reference voltage section until the voltages become correct - that is, match the numbers in the oval.

Also, double check the polarity of the capacitors you put in.


I just checked the voltage at the shorted PIN 1& 2 of R14 and the Negative (-) terminal. The reference voltage is only 25.5V when the Voltage regulator pot is at the maximum. It doesn't go above that. The reference voltage sections definitely seems to be the culprit as you mentioned.

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 Post subject: Re: Max Output voltage for all voltages less on Heathkit IP-
PostPosted: Aug Wed 14, 2019 10:25 pm 
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A special thanks to all the folks for all the suggestions . I have managed to finally fix the issue!!

@Scott thank you so much for helping me isolate the problem to the reference circuit part. Also @electricboyo I can’t thank you enough for the extremely in depth explanation and expected voltages at points.

As electricboyo mentioned I checked the all the resistors and they are like 97-99% close to the original values so they didn’t need to be changed.

The voltage across capacitor C1=205V. The voltage at junction point of R1, R2 & Z1 was 105V. Z3=66V at this point. Then I noticed something. One of the legs of the R9 resistor to ground had a solder blob but wasn’t touching ground. It was giving me 0V across but the resistance was 203 ohm. So. After soldering it back I checked the voltage across it and it showed 3.59V. After redoing the calibration procedure at this point for the zener current and voltage calibration, now the output voltages are exactly what it should be.

I again took all the measurements and they seemed be same as per the schematics except for the voltages before and after the zener current pot. It’s slightly off but I guess it should be fine. I’m getting like 64VDC and 51.4VDC at these points. The R9 volts is also 4.2V.

Here are the updated E3 (DC voltages):

5.8V
9.7
14.7
19.8
24.8
29.8
34.9
39.8
44.9
49.9

This looks very close to the schematic values. Now the only thing remaining is replacing the 75V 3000uF filter capacitor. I had initially put a new capacitor, but after coming across this issue I put back the original capacitor thinking the capacitor might have caused an issue. The new replacement capacitor was also 75V but it is 6000uF.

Once again thank you so much guys & gals!!! :D

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 Post subject: Re: Very low output voltage on Heathkit IP-27
PostPosted: Aug Thu 15, 2019 2:03 pm 
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Guys,

Today I changed the large filter capacitor and adjusted calibration and was in the last stage of checking the DC calibration with a 25W resistor . But unfortunately due to my bad luck I accidentally touched the wires together after the calibration and messed up the supply. Now the relay is clicking continuously. As per the manual the suspects could be Q2, Q4 & Q5. I checked with Diode tester on multimeter both the Q2 7Q3 to compare both since they are Germanium. They are both identical giving the impression that they are fine. The fact that the supply was loaded gave me the feeling that one of the regulator transistor is shorted. :cry: :cry:

So, I pulled out both the Q4 & Q5 transistor. After that I powered ON the supply and noticed the relay clicking ON and OFF was gone. I tested both the 2N2869 transistors and got the following results(The positive + symbol indicates the multimeter + lead was connector to that particular pin):

For transistor No#1

Base - Emitter (+): 103
Base - Collector (+): 102
Emitter to collector (+): 66


For transistor No#2

Base - Emitter (+): 103
Base - Collector (+): 102
Emitter to collector (+): 000 (tried changing the leads of the multimeter but still dead short)

So, the second transistor is blown. I tried putting back transistor no#1 and the power supply was working fine now. The needle on the meter was moving normally just that it wouldn't go to full voltage when the fine voltage knob was at max.

Looking online I found that these transistors are very expensive. I brought the entire supply for $30 and $18 shipping. The transistor costs like $27 alone. Where can I find one at a reasonable price or is there any Silicon replacement that can be put directly?

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 Post subject: Re: Very low output voltage on Heathkit IP-27
PostPosted: Aug Thu 15, 2019 2:22 pm 
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Post a WTB ad in our classifieds. Someone may have one. It probably has a cross to an NTE, ECG or other general replacement as well

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 Post subject: Re: Very low output voltage on Heathkit IP-27
PostPosted: Aug Thu 15, 2019 8:47 pm 
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Right now one of our community members have contacted me with a similar replacement transistor but its almost like an equivalent. The offered transistor is a Motorola SP1484 (NTE Equivalent NTE121). The original 2N2869 is a NTE104 equivalent. I've attached the data sheets for both below. Please take a look at the both and let me know if the Motorola SP1484 is a good substitute.

Motorola SP1484
http://www.weisd.com/store2/NTE121.pdf

2N2869
http://www.weisd.com/store2/NTE104.pdf

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 Post subject: Re: Very low output voltage on Heathkit IP-27
PostPosted: Aug Thu 15, 2019 10:37 pm 
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I would use the MJ2955:

https://www.mouser.com/ds/2/68/2n3055-1108522.pdf

There’s no problem at all replacing the original germanium output transistors with silicon for this particular case. There will be no change in performance. No other parts will need to be altered.

One thing is important: You must replace BOTH of the original germanium output transistors, even though one of them is still good. It isn’t feasible to have a mismatch. But everything will work perfectly if you install a pair of MJ2955.

-EB


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 Post subject: Re: Very low output voltage on Heathkit IP-27
PostPosted: Aug Fri 16, 2019 8:55 am 
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Check out this ARF thread regarding the IP-27:

viewtopic.php?f=8&t=216509

Poster Tim Tress replaced the 2N2869's with 2N6331's: the 2N6331 subs to an NTE-180.


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 Post subject: Re: Very low output voltage on Heathkit IP-27
PostPosted: Aug Fri 16, 2019 2:54 pm 
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The MJ2955 will also work; I think that is what I have in there now. Interestingly, the current limiting circuit will only work with a germanium transistor; I converted everything else to silicon.

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